Over Heating Cherokee Part 2 - AUSJEEPOFFROAD.COM

Jeepdownunder · #1 10-11-2002

New stock radiator on Monday. I'll report if it has helped.

[ 16 November 2002, 11:21 AM: Message edited by: Jeepdownunder ]

Gordo · #2 11-11-2002

Others have probably heard bout these b4 too buuuut..

Aussie Desert Coolers do awesome radiators for Cherokees for about $500.00. Check latest Just 4x4s for ad. They have multiple cores like others but the coolant flows through 3 times before exiting (prob the same ad you got the clipping from ??).

A mate had one of their radiators in a stroked 400 Chev equipped HJ ute in the last Summernats burnout comp. Temp Didn't go about 90deg C for a 10 min burnout !

Aussie Desert Cooler
350 Murray St Preston 3072 (03) 9328 4321

[ 11 November 2002, 11:08 AM: Message edited by: Gordo ]

dxj · #3 11-11-2002

Hi,

I had thought about these before but in reality isn't the water going three times as fast through a three times longer ( more tortuous) path? Isn't this same cooling effect?

I think maybe someone else could claim:-
We have a one pass radiator three times wider so the water goes three times slower through the cooling air and cools 15% better.

The oldest claim of all... Mine is long and skinny, yours is short and fat [img]graemlins/moon.gif[/img] [img]graemlins/avid.gif[/img] [img]graemlins/spinrhead.gif[/img]

I think I would need to see real independant test before I was convinced.
I believe claims for more fin density, more cores and more water capacity but which path the water flows sounds marginal at best to me.

Having said all that, it is probably a higher capacity radiator anyway ( with gimick three way stuff ) which works much better.

Most of the time just replacing your old, scaly insides, radiator with a new one gives you something like 20% better cooling anyway.

I figure the extra core you are talking about will have far bigger effect. Long ago when HQ holdens were new, a change for overheating was to go from 2 core radiator for 6 cyl, buy a 4 core for 350 V8. Remove engine fan, fit Davies craig electric. Fitted straight in, almost never needed fan at all!

There is a wrecker advertising an XJ for pieces in the trading post this week in Sydney maybe he has a radiator cheap?

Jeepdownunder · #4 11-11-2002

Thanks cooling is about more water being cooled. Extra cores to help. I'm sceptical about triple flow as well, but if it keeps the same water in the airflow longer it must help I think. All I need is a second hand radiator and I'm going to get an extra core rad made. New rad is $620-00 trade. I called the guy from the above ad, he said give me a radiator and I'll do a 4 core triple flow for $350-00. I think thats good we just need to see if a 4 core will fit, if not 3 core has to better than the pathetic little engine cooker XJs have in the front.

Gojeep · #5 11-11-2002

You have the problem too that you have a auto cooler in the right hand tank and as it says you cant then have the triple flow unless you fit a bigger external cooler than the secondary one that we now have as well.
What would be best in the Brass, Copper, Alloy core. When he spoke to Mark he said that the alloy would loose too much heat when outside temps went down when in a shaded valley. I would thought that the thermostat would be quick enough but this guy seems to think not! I think copper would be next bestr at transfer heat than brass due to its thermal properties.

Any comment.

Jeepdownunder · #6 12-11-2002

Yeah your right about the auto cooler. Maybe a 3 or 4 core radiator will help. I may get a new rad and have the old one made up to 3 or 4 core if I cant find a second hand radiator.

dxj · #7 12-11-2002

Hi again,

I think they claim there is little change in water flow restriction, ie water flow rate through radiator must be nearly the same!

Only way the water spends more time in the radiator is if you restrict flow rate so it takes longer. I think slowing it by restriction will do as much harm as good.

They are really claiming same water flow through radiator, just goes a zig-zag three times longer path, so it **must** be travelling three times quicker per fin area to keep the water pumping rate the same. So I am still skeptical.

Now if they admit to restricting flow rate to one third then water takes three time longer in the radiator.... but you only get one third the cooling due to one third the water flow!
I just can't see how same surface area water to air gives three times cooling no matter which way the water flow.

I stick by my claim that they probably have larger water capacity and/or fin density for the improvement.

Jeepdownunder · #8 13-11-2002

Thnking Thinking Uuuuuuuuuuuummmmmmm DXJ & Wooders have made me Thinking Thinking. Actually all good points merit in both? Thinking Thinking [img]graemlins/smoker.gif[/img] Cooling I think is about more HTO circulating slowing it down would actually heat it up. I think more water wishing through at a normal rate is the way to go. Larger core's in two rows is probably the best. Still thinking about this [img]graemlins/smoker.gif[/img]

Gojeep · #9 13-11-2002

The only thing is Wooders is that Mark has always had a problem with the stock radiator letting the car run hot and I had the same trouble from new with my first one. The one ( '95 ) I have now only has a problem while towing on very long hills in hot temps but apart from that it is much better than the first one even though it was made in the same year but just 10 months later [img]graemlins/dunno.gif[/img] This engine is smoother than the first as well so wonder if it has the '96 update where they changed the piston shirt design and added stiffeners to the block. Maybe they made a cooling chance as well as they were getting plenty of complains about it.
The funny thing was that the very first XJ's that came out had the ZJ V8 hood vents added to cope with the heat over hear but they removed them soon after.
I have a brand new set of hood vents from a 260z that will fit but as I dont have much of a cooling problem I am thinking of fitting smaller ones to keep the wife happy :rolleyes: If anyone wants them they can have them for trade price as I cant return them as were special order.

Wooders · #10 13-11-2002

If the engine is stock, I don't see why the stock radiator would be insufficient.
Personally I would NOT get a 4core and wou;d not rush to install a 3 core either as I feel they more obstruct the air flow - which at the end of the day is your prime cooling process.
Instead I would be looking to improve the air flow from the engine bay - first up hot air rises - I'd be fitting those bonnet lovours....

dxj · #11 13-11-2002

Hi,

I take on board Wooders point however I think the biggest problem in Cherokees is lack of capacity, for water and lack of surface area for the air to water interface. Jeeps aren't known for their "generosity" in the cooling stakes.
I vote for more cores and finer fins as it solves both of those problems.

Going to three or four core adds water capacity which means the water flow rate in engine is the same but in radiator is slower, ie more cooling effect. Just image example 10 litre cooling system. 5L in engine, 5L in radiate/hoses etc.

If you now have 7L in radiator then water travels 40% slower through cores but same rate in engine. Much longer exposure to air == cooler.

Now while water is going slower it nearly 50 or even 100% more surface area to air in 3 or 4 core so we have air/water cooling effect now 1.4 * 1.5 = 2.1 times ie 210% better air to water cooling for 3 core. 4 core would approach 280% better.

The air flow restriction issue is there but nowhere near 200%. The slower air is only an issue if the air becomes heated so that it approaches the temp of the coolant... ie it doesn't cool anymore. In this case faster air flow is good. Of course if you have a fixed radiator etc size then the only way to increase cooling is to increase air flow, hence aftermarket electric fans etc.

So maybe drop cooling say 25% for slower air through finer fins still gives 150 or 180% improvement with more core radiator.

In practice what happens?

Nearly all manufacturers use 3 or 4 cores in cars where extra cooling is required in same area.
Ford, Holden etc etc all normally use 2 core for stock 6 cyl. then go more cores and finer fins and more water capacity for performance engines or V8. I gave the example of HQ holden. They had three radiator sizes. 2 core 6 cyl, 3 core 4.2 & 5L V8 and 4 core 5.7L. All fitted same size aperture in front panel. I believe same applies 6 vs v8 new commodores and falcons.

For XJs? Common conversion in the US is 3 core finer fins radiator which they claim solves all. Some of the US XJ list guys have group buys for these.

Has anyone fitted one of those electric water pumps? I think the idea is that another cooling system limit is the water flow rate through the engine is set by the revs since water pump is crank driven. I think the idea is that for some engines sometimes just faster water flow gets the heat out of the engine and into the radiator.
Interested to hear if anyone has used one of these.

Gojeep · #12 14-11-2002

I agree with the above Ron as I could not keep my 400 chev in the Hilux cool until I swapped out the 3 row for a 5 row with fine fins of the same size.
I looked into the electric pump but when I asked them if you could run it submerged under water while doing a creek crossing they would not say if I could or not! That was not good enough for me as well as the fact that it is only rated to run a certain number of hours before needing replacing! :rolleyes:

Jeepdownunder · #13 14-11-2002

I think more water is the key without slowing it down to much. So 3 or 4 core. I think I'll put in a new rad and then have the old one made up with extra water core. I can't seem to find a second hand radiator for love nor money. I have replaced the water pump,flushed the system replaced belt, idler pulley, hoses and thermostat. In traffic even on a mild day approaching the red, Hot day in the red if aircon is on or if idling in traffic. With the weather heating up its either $620-00 for a rad or $3000 for an engine after being cooked. Not to mention what is happening in the transmission with the oil being cooked in the pathetic radiator. I'll be interested to see what happens with the new radiator. As I don't know what crap is in mine now or what crap the previuos owner put through it. I also think there is a lot of logic in DXJ's post as well as some good old fashioned physics principles. Also because I have LPG the water is re-routed to a degree that may play a small role. I usually run on petrol because GAS is not what its cracked up to be.

[ 14 November 2002, 09:31 PM: Message edited by: Jeepdownunder ]

Jeepdownunder · #14 14-11-2002

Also can anyone explain the correct way to check the viscus fan is working correctly. I have never really grasped how they work. I always thought they should free wheel when cold and be stiffer when hot. But some one told me I've got all wrong [img]graemlins/dunno.gif[/img]

[ 15 November 2002, 04:08 AM: Message edited by: Jeepdownunder ]

dxj · #15 14-11-2002

Hi again Jeepdownunder,

All that talk of overheat when most stuff is replaced makes me think maybe you are chasing some other problem here. I know all Jeeps are not fitted with your average tropical cooling system but they shouldn't be that bad either.

BTW I have LPG Holden, LPG motors do run hotter, but you say you are on petrol most of the time?

I agree on the LPG is no longer viable point too. Oil companies are getting to greedy. Whatever happened to when it was 19 cents per litre 6 yrs ago. Costs up to 3 times that now.

Do you know if you have a cooling system "scale" and rust problem.

Maybe take out the thermostat and see if lots of gunk in the head?

Maybe even worth having the engine cooling jacket chemically cleaned?

Worth checking above things as no radiator or cooling system will solve a gunked up engine block

Regards the viscous fan.

There are two types, some have a negative temp coefficient silicon fluid which is liquid when cold and thickens/expands when hot. These always drag but only when heat makes fluid expand does the impeller system in the fan hub "bite" and make the fan run hard.

Second type has fluid in it as well but has a little bi-metal strip that engages the impeller so that the fan spins.

First type always runs just with much less power when cold. Sort of like a high slip torque converter that goes low slip when hot. Often roars for 10 mins after startup until the silicon fluid settles out. Can change how much cold "bite" by adding fluid to the impeller.

Second type freewheels when cold, can usually be stopped by hand ( extra, extra carefully, don't try this at home ). Bites very solid when hot.

My XJ diesel has the first type. Don't know what the 4L has.

My opinion:- put in 4 core radiator and just have thermostatic electric fan or two. Big engine fans only really deliver big air at high revs and roar heaps when doing it. Electric matches or betters them at low revs.
Holden, Ford and others no longer use engine fans at all even on V8 performance motors.

Jeepdownunder · #16 15-11-2002

Thanks for the tech info. I'll work out what mine is. I have replaced the thermostat and it was as clean as a whistle. But I may not see all the scale if its built up and is not floating around. Also I have used a chemical cleaner and it shifted nothing at all. I've ordered a new radiator today I'm bunging it in Monday as I'm not at work. I'll then get the old one pulled apart so I can see inside, then I'll make a 3 or 4 core out of that. If the new radiator solves the problem I may sell it at trade to some one and put in my new extra core rad I have made or vise versa. Also i think you may have a point about just having electric and piss the viscus fan off ;)

Jeepdownunder · #17 16-11-2002

I notice the fan is free when the engine is HOT and stiff when COLD. This sound back to front to me????