4.0l XJ Overheating
 

4.0L XJ OVERHEATING PART 1: START HERE - THE BASICS!

So your 4.0L XJ is running hot or overheating. What to do? It’s the most commonly asked question on these pages and you will find many interpretations, causes and solutions. These are some basic guidelines to follow that should answer some questions before they get asked. While some of the information provided here comes straight from the FSM, most of it is my own opinion which is based in particular upon years of examining countless different XJs (hundreds in fact) with varying levels of system integrity, modifications and usage. Naturally these opinions are open for debate (which I encourage) as no one knows everything! For the purposes of this discussion we will be focusing ONLY on the 4.0L petrol engine and generally in stock form so as to create a benchmark for failures and modifications. So please don’t ask about diesels as that is a whole other ball of wax. The following info should give you a good indication of what you can expect from your cooling system and how to identify and address common issues.

XJs are notorious for running warm - it’s the number one issue 4.0L owners face here in Oz. This is largely due to the fact they were NEVER designed to use the big straight six 4.0L; the Cherokee came out in 1983 with a horribly underpowered little V6 until Jeep realized what a disaster it was. So they shoe-horned the big 4.0L into the already cramped engine compartment. As a result, this configuration produced an abnormal amount of ambient heat being trapped under the bonnet with nowhere to vent it (not to mention an inadequately undersized radiator). Add to this our RHD radiators run the tranny heat exchanger on the hot side of the radiator as opposed to US designs. So not only is it a poorly thought-out system to begin with, but our Ozzy imports suffer additionally from the conversion process.

So what's too hot and what's normal? Interpretation of this is highly subjective and will vary with operating conditions, mods and system integrity but the design actually allows for very hot temps within normal operating parameters (almost to 117*C which is virtually redline on the gauge). Generally, operating temps can fluctuate anywhere around 95-112*C in normal driving conditions but ideally about 108*C is max. Personally, I consider anything over 112*C on a hot day suspect but the system shouldn’t actually boil over until it hits the redline. So between 112*C and 117*C (boil over) you should watch things very closely. If possible, stop, place the tranny in neutral with the engine running and set the heater on high fan. This should let things cool off enough so you can continue on. High ambient temperatures coupled with stop and go traffic, towing, extended 4 wheeling in the sand and extended 4 LO climbs can aggravate a properly functioning system even on its best day. Outside influences can impact temps to a large degree and push the system beyond its capabilities quite easily so always proceed with caution. It shouldn’t be like this but it is so just accept it - it’s a Cherokee thing. Expecting more than that isn’t going to lower the temps so mod away and/or repair things till you get it where you want it. If this isn’t your cup of tea then don’t buy an XJ because you are likely going to deal with it sooner or later.

If you have an obvious problem such as a leaking radiator you need to consider the whole picture and not just the issue at hand. Of course you can replace the radiator but you need to know why it failed in the first place - was it just component failure or is there is a bigger issue looming in the background. The integrity of the system is very dependent on maintenance but normal wear and tear is going to happen no matter how well you take care of things. However, proper maintenance can prevent issues and extend system life greatly. If you do no other maintenance on your XJ at least maintain the cooling system - it’s a very delicate design so take care of it! I know this sounds like dribble and you've heard it a thousand times before but I can’t emphasize how critical it is. If you fob it off and have a problem you then you don’t deserve to complain - fix it and move on. Maintenance and repairs are never free no matter what you drive so don’t whine about spending money on your car's health - if this is you then maybe bicycles and trains are more your speed. And not having funds to repair stuff properly or doing a "bandaid" solution is only going to get you more grief – you can expect it.

What to look for when evaluating your cooling system:
1 - Ask yourself this: "How long have I had the car and what do I know about its history regarding repairs and maintenance?" If you bought the car recently then assume nothing has been done and start from scratch. Take service records with a grain of salt as they can be misinterpreted or even incorrect. Example: if your water pump looks brand new then it probably is but how do you know the correct pump was fitted? Did someone install a non-reverse flow impeller unit by mistake? And what concentration of coolant was used? Was the system pressure tested after the repair to evaluate other potential concerns? Is it a cheap pump with a short life span? You simply don’t know by looking so don’t assume anything. If you have owned the car for over 2 years and haven’t touched the cooling system then assume you need a complete evaluation and more than likely some form of servicing.

2 - Evaluate the system: Check the coolant level. The radiator should be completely full when hot and the overflow bottle should be at the "full” or “full hot" mark. If not, then you are losing coolant (or it wasn’t serviced properly to begin with). Check the coolant condition - it should be a 50/50 mix of alloy-friendly ethylene glycol/distilled water (DO NOT USE POLYPROYLENE GLYCOL) and the concentration should read at least +128*C to -20*C using a coolant tester. Watered down coolant will lower the boiling point and raise operating temps. Maintain at least a minimum of 44% ethylene glycol and don’t EVER run straight water (except in emergencies). Do not run without a thermostat or the engine will begin to form sludge from condensation in the crankcase which will cause long term engine damage (condensation is water and not the best thing for lubricating bearings). You should not see oil, rust or flaking in the coolant. If it doesn’t match this criteria then flush it thoroughly and/or make appropriate repairs. If you have rust in the system you have big problems. You will never get rid of it completely unless every last component (including the block) is boiled out and/or replaced. The cheaper solution is to flush it every year which should be adequate in these cases although components will have shorter life spans. Normally, the system should be flushed every 3-4 years. Make sure you use quality coolant with anti-corrosives and rust inhibitors along with distilled water (do NOT use tap water). Check the system visually for signs of leaks using a pressure tester while the engine is hot and use a bright torch so you can see any smaller seeps. You are looking for the obvious wet stuff but also look closely for past or intermittent leaks as evidenced by white or green crusty flaking, build up and dry runs. If you find a leak, fix it and then retest it again as a big leak will mask a smaller leak - never assume you fixed it all in one hit. Also make sure you pressure test the radiator cap for proper operation. It should hold at the specified pressure rating stamped into the cap (16 or 18psi depending on year) and release pressure a few psi above this (18-20psi). Caps generally should be replaced every 2-3 years as a rule of thumb. They are a common failure but play a big role and are often overlooked even by shops. A cap which doesn’t hold the specified pressure will lower the boiling point of the system which can lead to warmer running temps.

2A - Places to inspect for leaks: all hoses/connections, the radiator (especially along the driver side tank seam), both tranny cooler line connections to the radiator, the thermostat housing/gasket, the water pump/gasket and water pump weep hole located on top of the bearing housing and the welsh/freeze plugs - there are 5 plugs on the passenger side of the block plus one in the back of the cylinder head. A 7th plug is hidden between the engine and transmission and cannot be seen directly so watch for coolant at the bottom of the transmission bellhousing. Also check the heater control valve ('96 units only) and also the heater core itself. If the heater core is leaking you may note coolant coming out of the condensation drain tube located on the bottom passenger side of the firewall in the engine bay and/or a wet carpet on the passenger floor (make sure you peel the carpet back and check for moisture directly on the floorboard). Check that the heater is actually putting out heat; if not you may have a restriction in the heater core, a water pump impeller that is spinning on the shaft (especially cheap pumps with plastic impellers), corroded/damaged water pump impeller fins or air in the system. Another way to check this is to feel the heater hoses near the firewall when the engine is hot - if they are only warm (not hot) then the water pump is failing and not providing the required circulation. When pressure testing and noting a loss of pressure but you don’t see any leaks then coolant is probably going out the exhaust which usually means a cracked head. Inspect the cylinder head gasket line on the block for evidence of leaks and remove the spark plugs and check them for coolant contamination. You can also shine a light into the cylinders through the spark plug holes and see if any of the piston tops are shiny and clean (in comparison to the rest of the pistons). If you see this then you are getting coolant into the combustion chamber and out the tailpipe. This will be accompanied by an unexplained loss of coolant while driving without any visual leaks and the engine may be misfiring or running rough. A compression and block test can further verify this although sometimes you won’t find the problem until the head is actually removed and pressure tested/magna-fluxed at a machine shop. Water on the dipstick or oil in the coolant is a dead giveaway of a cracked head or blown head gasket so get it fixed pronto and don’t drive it until you do!

3 - Other things to check: Inspect the components of the system. Check the fan belt for slipping, glazing and improper tension. Check the condition of all the hoses - they should not be brittle, swollen or extremely soft and should not exhibit rot, rust or scaling inside. If they are over 5-6 years old then they are probably due for replacement as normal preventative maintenance. Also replace the thermostat every 2-3 years as preventative maintenance and make sure you ONLY install a 195*F unit - DO NOT USE ANY OTHER TEMP-RATED T-STAT! Check to make sure the electric auxiliary fan comes on when fully hot and that it comes on automatically with the AC or defroster switched on. Check the fan clutch for proper operation: with the motor stone cold and turned off it should freewheel with some light resistance but not more than five revolutions. If it doesn’t spin at all or is locked up replace it. Start the engine when stone cold (best done after sitting overnight) and listen for fan noise to increase as rpms increase (a normal condition). If fan pitch noise does not increase with rpms then the fan clutch is bad and needs replacement. As the engine warms up fan noise will gradually decrease (again, a normal condition). You will also hear the fan roar on initial start up then die down within 15 seconds or so (also normal). Once the engine is fully warm use a rolled up newspaper and insert it into the base of the moving fan blades. You should not be able to easily stop the fan from turning - if you can stop it then the fan clutch is defective and should be replaced. Also check that the fan clutch is not leaking oil - if it is, replace it. Make sure your fan shrouds are in place and intact - removal or trimming of the shrouds can be detrimental to airflow output from the fans. Check all the grounds for your aftermarket accessories (spotty, winches, radios etc) to ensure they are making good connections to the chassis, engine and battery. Poor grounds between the chassis, engine and battery can promote excessive electrical flow through the cooling system causing pitting and erosion (electrolysis) of metal components like welsh plugs, water pump impellers and thermostat housings. Make sure your engine and transmission oils are full, fresh and able to dissipate heat properly (oils don’t just lubricate, they also remove heat). Check that your spark plugs are the correct heat range and not producing excessive firing temps in the combustion chamber. Check the computer for stored codes - a malfunctioning system, sensor or wrong application/stuck thermostat can sometimes set a code or check engine light.

4 - Airflow and coolant flow: Check the radiator for restrictions in the core (a very common problem often overlooked). Check for airflow restrictions through the radiator. Blow out the fins in the radiator, AC condenser and tranny cooler from the engine side outwards row by row with compressed air (pay particular attention to the bottom and sides where debris build up accumulates). Make sure the fins are straight and not bent over preventing airflow through the core (use a small flat tip screwdriver to straighten them – a time consuming process but essential). Also ensure you haven’t compromised airflow by adding too many accessories directly in the path of the radiator (nudge bars, spotties, winches etc). While some amount of airflow disruption probably won’t affect things a lot there is great debate about what is too much. Use your discretion here but know you will affect airflow by adding too many accessories. There is also some debate about whether removal of the air dam and/or skid plate affects temps. Personally, I’ve found this unproven but again, be aware of potential effects. Rule of thumb: if you modify something and notice a negative impact which is causing you concern REMOVE IT!

When time allows I will post a follow-up to this info in the next section: "4.0L XJ OVERHEATING Part 2: Cooling System Failures and Repairs" and later we will have a third discussion: "4.0L XJ OVERHEATING Part 3: Cooling System Modifications".

Wow!!Now that's a write up. Gonna take a it of time to read too:)

I feel a 'sticky' coming on :D
Well done Rodge, I'll read it when I have time ;)

Real good read Rodge .... and I trust parts 2 & 3 will be equally as good. :cool:

Couple of discussion points .......

50/50 antifreeze is a northern hemisphere ratio .... ideal for -37'c temperatures .... but only satisfactory, in constantly warmer climates unless the cooling system is designed for 50/50 AND the climate.

Yes yes everyone ... new holdens & fords specify it now too ... and what continent are those companies head offices and rulemakers at ???? :rolleyes:

If you choose to use 50/50 anti-freeze - ensure your cooling system is top notch ...

Definitely lowers the boiling point ...... by less than 3*c at 0psi actually .... but wont nescessarily raise operating temps - as lesser ratios of eth-gly to water, cool better.

50/50 doesnt shed heat in the radiator as efficiently and goes back to the engine hotter than what a 30/70 mix, or less, will - from the same radiator.

Watered down 50/50 is definitely incorrect to use because that means the additives have also been watered down ... but a quality, commercially available 30/70 anti-freeze pre-mix, will have all the correct corrosion additive amounts to protect your aluminium radiator, and some for the cast iron ..... per litre of fluid ... for those that choose to use it.




Like the minimally efficient cooling system which is designed for much lower average temperature use than here ..... so is the thermostat heating device.

Either ensure the cooling system is capable of not allowing the engine temp to get above the initial danger point indicated by the temp used by the PCM to operate the aux fan,

Or run a lower temp thermostat that provides a lower, constant, engine running temp that doesnt interfere with the vehicles normal running requirements.



Polite enough so as not to start a war I hope Rodge ... :%

i use cat elc in both my xj and the wifes xj
this is top notch stuff
mine is deisel hers is petrol
mine runs at 90 has vents
hers at 97 has a cowl bonnett
did a total cooling system change on both 2 weeks ago

Why?? If the car was designed to run at 195F, why lower it? It won't stop it from overheating if the cooling system is not up to scratch.. and the car will not run at the PCM programmed temp.

Who says it was ONLY designed to run at 195" ??? ..... Cerainly not the little fella that listed the 180" thermostat in an XJ parts manual.

Why lower it .... ??? ......... Why use a bit of thicker wire than nescessary for the intended amperage load ???

And which PCM programmed temp are we talking about .....
The P0125 -6*c one that is too cold ?,
The -5*c one that wouldnt be too cold ?,
The 70*c warm up cycle trip definition temp in the FSM ?,
The temp everyone thinks is the operating temp just because its labelled on the hit & miss dashboard gauge ?,
Or maybe the 20*c that just happens to be the fluid temp - when the heated O2 sensors have reached their operating temp and trigger closed loop as long as you're in idle or cruise modes ?,
Cant imagine it would be a 92*c temp coz that temp reference doesnt exist in the FSM .... as a running temp.

Its all old hat Nakkas .... Been done to death before. Have a real good read of sections 14 & 25 in your FSM ... Even tho most temp data seems to have been censored out in the later editions - theres enough info in there to grasp the Fuel Injection system operation .... If you take the time ...... altho you should be swotting up on the V8 manual now.

i am with carves on this one i run a 160 thermostate and all good
cheers dazza
(also to acording to the book 160 thermostate is fine or they would not make it and sell it in aus)

I run a cooler thermostat and the truck seems to still sit on the exactly the same temps as it did with the standard thermo just takes a little longer to get there. Cant say I have seen any detrimental effects.

Brilliant thanks, I look forward to the next installment.

Got yer stroker in yet!!

Excellent write up there Rodge, look forward ot the next installments....

Interestingly in the 94-96 parts manual (my model) it lists only 2 thermostats, an unrated unit and a 180* (severe use) unit. Another interesting thing is my '95 model had a radiator in it specified for a '94 model and I thought it was alloy/plastic when in fact when I removed it recently I found that it was actually copper/plastic and had been there at least 8yrs as that is how long I have owned it and only once did I have an issue of overheating!!!!!

I drove my xj into the workshop at lunch & hooked her up to the jeep Techconnec just to run her numbers & check for any ecm pcm updates & low & behold what popped up HIGH AMBIENT OR HOT SOAK TEMPERATURES 2000 - 2001 XJ its a software update that lowers the temp threshold used to determine when the engine fans are turned on , Cooling fans will cycle more often .

Service Bulletin 18-031-03 18-039-03

Ran the PCM update & my thermos used to come on at 104 c to 105 c now they come on at about 98c or by the temp gage a needle width before 100c & thats where it stays , im pretty happy with that , but i have also just fully replaced all the cooling system & removed the AC gear so i have greater air flow through the front so it may vary a little from Jeep TO Jeep ;)

PCM update & re-program is for 4.0 ltr Auto's only


Top work there Rodger , cant wait to read the followups & sorry for the little Hijack but i thinkk it may also help the update xjer's ;)

excellent comments and rebuttals guys! exactly why i encouraged it (dont worry Carves, your opinions are safe - everyone has one so always share). I just thought it would be nice to have this discussion which has been beat to death countless times in one place: RIGHT HERE! i wont hold my breathe but maybe it will slow down the repeat questions we all get. sometimes i wish i had a stamp when answering them lol. :cool:

Luckily for us that is all we got here....

http://www.freesmileys.org/smileys/smiley-happy057.gif ... Best I tie an icecube to my typing finger and get started then ... :mrgreen:

Nahhhhh ... I'll be fairly shush on this thread http://www.freesmileys.org/smileys/smiley-scared003.gif .... as you covered most of my gripes & concerns at the start.


Can you use the techconnec thingy to find out whether that computer flash can be done on any OBDII 4.0l XJ here.

I mentioned it as only being suitable for the 2000/2001 in the other, general cooling thread last year, coz my local dealer reckoned it was year model specific .... but the dealers say a lot of things .... ;)


Best you check for belly dancers & camels under the backseat jj - as that was the stock radiator for the hot climate, saudi/middle east market ... was also available as a heavyduty cooling option elsewhere .... If the dealer knew about it :roll:

Should be in your parts book too.

It was listed in the parts book, that is how I know it is from a '94 model, maybe this is part of the reason that I had so little cooling issues.....
Buggered if I know what thermostat is in it though as I have never checked..... oops!!!

Goes in Monday:) Just waiting on Brown Dog engine mounts and brackets.

LMAO that they do mate ILL double check for you , i have a print out of the bulletin & it is year specific 2000 / 2001 Has to do with emission changes its mainly for the 01 xjs but will also do 00 xjs if they have NAE sales code what ever the hell that is lol

I wanted MY01XJ number plates after i sold my wrangler.. I went to the RTA website, checked the availability.. alls good.. then when i had the cash to spare.. went to order them.. not available!! LO and BEHOLD!!

sorry, but what do number plates have to do with cooling systems? maybe that should be in the "What did you do to your XJ today" thread (hint hint) :blah::blah::blah:

Cool number plates = cool jeep...

this is why we have a problem here we have knoledgable people being pissed of by people posting totaly non relevent crap in the tech info threads

Rodge, why the recommend minimum 44% mix? A lot a fellas are recommending and running 33% ratio for our hotter climate. A lot of engines, consisting of the same materials and marketed to Australia are running 33% and don't have any shorter life span because of it.

im not pissed off, was just a friendly reminder that we are discussing the xj 4.0L cooling system here - not other irrelevant stuff. adding those comments just makes it harder for folks to wade through the posts to get the info they really need. even my post here adds to it so i will state this one time only: lets stay on topic please. its all good so dont anyone stress over my comment! :cool:

as for the 44% figure - that is straight out of the FSM but as others have pointed out it may not be suitable for warmer climates. my choice has always been to run a 50/50 mix but that is just me. i suppose too it should be clarified what is 30% and what is 70% - the water or the coolant? lets make that distinction for those people who may not know (remember, this is an info page). also remember, my original post is PURELY my own opinion based on my own experiences and guided loosely by the FSM - i WANT you guys to share YOUR opinions and why you think they are plausible. That way a consensus might be formed based on shared experiences. if 30/70 works tell us why - i hear that number a lot too and may change my thinking if i hear a good reason for it. i guess also i am from a cold region so that number from the FSM rings true for my past experiences but like everyone, i learn something new everyday! suppose i should know better without being told but sometimes ya just go with what ya know! keep it coming guys! :cool:

Thanks Rodge... great run down on one of the most commented/posted/talked about topics regarding the good O'll XJ... for a new comer to the brand of JEEP, its certainly great to read your experiences/comments... Ive changed most things on my cooling sys even putting in new welsh plugs when I got the jeep last year and shes running great here in hot/humid Brisbane..runs at 97deg in most instances, never goes over 105 in crawling daily traffic...I use a alloy friendly 50/50 mix of NULON ULTRA COOL.. it contains no Glycol. Its formulated to keep rust/scale /sludge/corosion and electolysis away... seems to work well.. I removed the bulky plenium chamber box that sits on the intake and fitted a older xj intake hose to stop heat soak, also removed the lower skid plate.

thanks
Steve

This is why I'm staying out of this thread from now on. We have stuffed a totally good piece of info and picked the crap out of it...

Nice try Rodge..

I was thinking I should post Rodge's thread on a web page like Go Jeeps, so it can't be cannon fodder....

50/50 ... 30/70
 

Good point Rodge .....

Generally the mix is referred to as eth-gly/water .... so 30/70 is 30% eth-gly.

But it only needs to be written or referred to once ... in the reverse - and its all out the window. :wall:

The ratio numbers have no real reference to the anti-corrosive additives, coz thats measured in teaspoons/tablespoons/whatever .... per litre of mix .... regardless what the mix ratio is.

Which coolant grade to use ... and even which type is a drivers choice depending on what they know or whether they are warranty bound.

There is 4 sources of anti-freeze mix info ... Ooooops ... 5 sources ... thanks Nakkas ...

First is all the knowledge, beliefs, experience, opinions, facts AND fairy tales on car forums,
Second is the "our coolant is special" drivel from the car manufacturers,
Third is what the "coolant" manufacturers will tell you before getting to the point of upsetting the carmakers,
Fourthly there is the coolant scientific community ... who dont seem to give a toss who they upset when quoting facts and figures ... Coz they are always right ... :rolleyes:
And lastly there is all those unchallangeable private websites with all their right AND wrong info.

I like to jumble it all together for a balanced view .... ;)

yes that is relevant in regards to % of coolant mix but as i said what the ****** has a rego plate got to do with cooling problems unless it blocks air flow
that post is just bull before giving me the toilet have a look at post # and join dates of people it
usually means something we have had a couple of realy cluee people leave becuase of the of topic crap that gets dumped in tech threads
by the way i have over 30 years of jeep experience under my belt
and over 35 years fab experience as well


http://www.ausjeepoffroad.com/forum/...ons/icon12.gif

Ok, I thought you were having a go directly at me, my bad (still a newbie myself, to all things forum). I think the number plate post was just a miss post though... I think...

Good point.

Got ya. Only reason I asked was not to pick the crap out of it, more that I have just flushed and replaced my coolant (30% Ethlene glycol). I was aware of the 50/50 and I guess it makes sense that the FSM would recommend this as you would top it up with distilled water (you would hope) during the coolant life, therefore watering down the mix

Good point, as per carves

i am coming to a conclusion from the replys already regarding the coolant and mix thing....ive always bought concentrate coolant and mixed it 50/50 with distilled water. my theory was why pay extra to some coolant company for their overpriced distilled water (or whatever form of water they use). but now after reading the comments about additives and ratios im thinking maybe this is a bad idea especially when it comes to the additives being watered down. i spoze one could just add some extra to the 50/50 but im thinking the cost is going to end up being the same. so why not buy good quality pre-mix with everything already at the correct ratios? ill be looking closely at the pre-mix brands next time i make a parts run. maybe Nulon, Castrol or Prestone have just what the dr ordered....i told you i would turn if i had a good reason!

Personally I have always used concentrate for the same reason. This time it was the castrol, but I have used tectaloy and others for my other cars without any complaints.

actually in hindsight i'm being premature about switching to pre-mix. if its formulated as concentrate then it should have the appropriate amount of additives to mix with distilled water to 50/50 or 30/70 or whatever the label calls for. so im gonna flip flop back :hammer:

I too use concentrate, rather than pre mix... Usally its Nulon or Tectaloy, as you mention... cheaper that way, plus was always concerned on how good the pre mix product is... ?

Good being able to thrash stuff out on an open forum huh :D

Personally I dont think theres a great deal of difference in the additive amounts in either a bottle of 50/50 concentrate or a 30/70 one but users should be aware there is.

Only real reason I use a premix is so that I can go anywhere and still be able to find the cheap, commonly available, one I use .... at almost any town with a halfarsed autoshop .... and not have to turn hicksville upside down hoping to find that "special" brand and a coupla bottles of distilled water.

so in Aust where the temps are warmer, its better to use a 30/70 coolant? i think i get that.

i gather water is better at absorbing heat than pure 100% eth-glycol???

so what coolant brands at 30% do you recommend to use in the 4.0L carves?

cheap and nasty, expensive or mediocre?

guys only prob i can see with diluted mix is the temps that engine runs at you could suffer explosive errosion on the the block barrel area
due to surface cavitation as coolant has a lower boil point
basic physics on latent heat point to boiling point is only 1 deg
now i am not saying cooling system boiling point but the area of interaction between coolant and barrell area
on the desiel these are wet liners i run cat elc 50/50 premix
and have no probs
the other thing regardless of brand pre mix is ready to go for a trail top up

Eth-Gly in addition to being an anti-freeze ... is a heat transferring item ... not so much a cooling product ... Gathers heat OK ... but needs a damned good heat exhanger unit (radiator) to lose the heat ...
Dont even mention using 100% eth-gly :lol:
60/40 Eth-Gly/Water ... is the max even chrysler recommends .... and is most useful for when on a polar bear hunt .... ;)

30/70 will give you a slight gain, as will a slightly lower thermostat rating and a better fanclutch etc. Its all dependant on how you approach your cooling system.

Gotta remember - A jeep ... or any other vehicle ... doesnt have a radiator, fanclutch or coolant etc ... It has a "cooling system" ... and the cooling system has a radiator, fanclutch, coolant etc.

Overall benefit is a mild combination of things rather than looking for a major "fix" with just one item.

I recommend a quality known brand with aust std ratings and the additives your vehicle needs .... and would be very shy on a Crazy Clarks special or any other mix offering miracle overheating cures ;)

For my own personal use ... I just use the tectaloy 60plus "type B" 10/90 mix and change it every 12mnths. Using a fancy 5yr longlife coolant to keep the ecofreaks happy doesnt rattle my chains ... But "type B" is not ideal if you have a heap of aluminium bits tho.

If I was spending some time down the snowy I would run a 30/70 ... even though I never used anti-freeze when I lived down there and the HR was a new holden release :D ...... I'd reckon a 30/70 mix in the Valvoline G-05 ( http://www.valvoline.com.au/files/productpdfs/52.pdf ) would probably be pretty good. G-05 is pretty much the formulae Mercedes has been using for donkeys ages apparrently ... and the other coolant brands have their versions.

With Rodges permission I might provide a bunch of eth-gly/water mix characteristics and the original tech site link in a later post ..... but I need to lay it out so that the individual bits of info arent misconstrued ...

So PM, post example, heading your way for approval in a few days Rodge.

no one needs my approval to post info - bring it on!