Jeep Cooling Basics

[bonza]

Some facts on thermodynamics

keeping it simple, heat is a product of energy (fuel) used to create work (horsepower). In other words not all the energy is used to create work due to inefficiencies such as friction. This energy is transferred off as useless heat that must be controlled. A definition and measure of energy 1 BTU requires heat to raise one Pound of water one degree Fahrenheit or 1 Calorie requires heat to raise one Kilogram of water one degree Celsius.

heat is transferred by convection, conduction and radiation (infra red).

heat will always transfer from a hot object to a cooler object

engine heat transfer is mostly accomplished by convection and conduction. Only a small amount of heat transfer is accomplished by infra red radiation

copper is the best conductor followed by aluminium followed by brass.

plastic as used for radiator header tanks, is a very poor conductor


the theory of heat transfer by convection such as coolant flow through radiator tubes and engine water jackets is extremely complex due to the laminar flow boundary layers of the coolant, hence the need for good quality coolant mixed to correct ratio.

basic law of radiation

black dull objects are good emitters and poor reflectors of infra red radiation
silver polished objects are poor emitters and good reflectors of infra red radiation

therefore a blackened aluminium radiator will emit heat quicker than the same radiator highly polished to a metallic sheen.

[bonza]

Radiators, more correctly heat exchangers

by design, coolant usually enters the top corner and is delivered to the pump via the other corresponding corner outlet diagonally opposite.

fluid will always follow a path offering the least resistance, usually on the extremities or sides of the radiator. therefore the inner tubes are the ones most likely to become plugged.

because not all the tubes are plugged a good flow can still be observed making troubleshooting difficult to determine if it is indeed plugged. best way is to feel the tubes for cold spots on the radiatore core as soon as the engine has been shutdown and if plugged the inner tubes in the centre are the ones that are likely to be blocked.

this has a two fold affect. not enough coolant is being cooled by the airflow passing over the tubes that are clear, and the tubes that are blocked being in front of the viscous clutch doesn't have hot air being generated by the radiator to expand the bi metal spring that is required to expand to switch the valve in the viscous clutch in order to lock it for the fan to rotate at maximum revs and blow the most cubic feet of air. not such a problem if you have electric fans

THE WRANGLER STOCK OEM RADIATOR
Plastic header tanks and aluminium core
Single row 55 tubes 8mm apart 28mm deep 1.4mm wide outside tube dimension 0.6mm wide internal tube dimension
narrow tubes make the stock radiator prone to plugging.
after 40,000 Kilometers mine was plugged with a soapy substance from the HOAT coolant

EBAY AFTER MARKET RADIATOR
Plastic header tanks and aluminium core
Single row 45 tubes 10mm apart 28mm deep 2mm wide outside tube dimension 1.1mm internal tube dimension

ok, Im repeating myself as I have posted this comment before, but it probably is the most important issue

[bonza]

water pumps

not much in them, an impellor, bearing and seals.

just make sure the bearing hasnt collapsed, the seals are ok and the impellor is intact. some impellors are steel and slowly rust away, collapsed bearing is obvoius as the shaft will be loose and a shot seal is determined by a pesky fluid lak from the weep hole until it becomes a gusher

you can get a hi volume pump, but pretty much useless if the stat housing isnt capable of receiving this extra delivery or so to with the radiator

[bonza]

thermostats

this is a repeat of guff Ive posted before, but if anyone is interested, here goes

Thermostats, a much maligned device and grossly misunderstood.

Stats are calibrated in degrees F or degrees C.

Jeep Wrangler OEM stats are specified 195 deg F (90.5 deg C)
Thermostats regulate minimum temperature set point.
If you have an overheating problem and the cause isn’t due to a sticking thermostat, then fitting a lower set point stat, say 74 deg C, wont cure the problem it will just allow the poppet to open at a lower temperature and remain open as the coolant slowly builds up temperature and much to the dismay of the driver the temperature indicator needle swings hard over into the red.
If the coolant system is in good condition fitting a 74 deg C stat will keep the engine temperature hovering 85 deg C well below the normal operating temperature of 100 deg C and probably cause poor fuel economy and unnecessary wear on the engine.

The temperature rating of the thermostat is the point that it begins to open and a conventional OEM 195 deg F stat is not fully open until coolant temperature reaches 215 deg F (102 deg C), which is just above boiling. However as the system is pressurised with a 18 PSI radiator cap and providing a suitable coolant is used, this raises the boiling point approximately another 50 deg F, giving a combined coolant temperature of 265 deg F / 130 deg C before boiling occurs.
This is fine if everything is in good condition, however it can be a problem if a 195 deg F regular stat is used and the rest of the system is little inefficient. This is evident with wild fluctuations of the temperature gauge needle. The needle can be observed to swing over rapidly into the red as the stat is cycling from closed to open in an effort to control coolant flow into the radiator and then go back to normal. That is why I fit a Hi flow or premium stat at the OEM set point of 195 deg F in order to eliminate the cycling problem of the stat’s poppet. Some people overcome this problem by fitting a 180 deg F stat,
(82 deg C), so full flow is available at about 93.5 deg C, a few degrees below the normal operating temperature, but this leads to cooler engine temperatures especially during Victorian winters when cold mornings are hovering around the zero degree mark.

In summary a Hi flow/premium stat will provide some latitude for cooling system defficiencies and smooth out lower and upper temps, but wont fix an overheat problem.

[bonza]

fans and viscous clutch

I fitted a seven blader and super severe duty clutch that locks up at a lower temperature and transmits greater torque thats required to shift a lot more air at 80% of engine revs. details are in the trouble shooting guide above

I would never fit an electric fan in lieu of a fan connected to a clutch. the fan I fitted is capable of shifting more cub meters of air than any electric fan.
maybe a different story for other jeep models

with the above mods to my Jeep, temps according to my scan gauge are stable at 89-105 in all conditions including 45 C days and 4x4 work.
before I use to see temps up to 125 when climbing up a steep hill. not anymore

thats about it for me, now Im gunna watch bear grylls survive the baja desert, huru

[carvesdodo]

Originally Posted by bigredtj

Carves is the cooling system king

Originally Posted by NT-Boy

Nice write-up KING CARVES........

Awwwww .. ... Ease up fellas ....

Court Jester is probably a more apt title ...

Most of this stuff used to be common knowledge once ..... seems to have been disregarded as not important ... since the advent of bling and bluetoothy I-fone thingymajigs becoming the most important components needed in a vehicle these days.

Still ... I suppose those things give ya something to do while waiting for the tilt tray or natrad or century batteries or ... or ....

Originally Posted by bigredtj

My TJ never overheated even baked in mud it sat perfect everytime.

Must just be an xj thing

Certainly is a major issue with the XJ azza ... but its also relevant with any vehicle from another areas sales market ...

Having had a TJ and a coupla XJs ... The TJ is more capable of handling the heat but still only just adequate ... Some tweaking for personal use makes all the difference .... Just like with suspension / tyres and stuff.

Originally Posted by bonza

Hmm, I think I can put something together about all of this, but will take time..some of which may be a repeat of stuff I've posted before

Geeez Bonza ... Ya stole all me thunder I had planned for post 2 ...

Good stuff tho .... and probably needs repeating regularly

Originally Posted by Auberon

I think we have, as a starting point,the Jeep towing its maximum rated load under "fairly" hostile conditions....and that is indicative of our design reserve.....not much really.

The Jeeps are a good framework to build improvements into.

So true Auberon

Straight off the showroom floor - they at operating at their ... best ?
...... and then many expect more from the vehicle ... in our environment .... and get surprised when the temp gauge behaves like a tacho gauge or the auto gearbox starts smoking

Heated mirrors, heated seats, excellent interior heating, factory fitted foglights .... Just what sort of sales market is that all aimed at ? ....

[Steve F]

I've always wondered why so many have so many cooling issues. My 2000 XJ towed my camper up the bells line of road over Australia day last year when we were hitting 45c. The camper weighs about 550KG loaded and the XJ is on 3.55's with 32x11.5x15. This is pretty much the worst condition my XJ has seen, on top of that it had a leaking radiator (replaced when I got back with an Adrad). I had no overheating issues, sure it got warm but nowhere near the 'red'.

I've since replaced the radiator and as preventative maintenance replaced the hoses. Other than that the rest of the cooling system is stock with 140000km on it. Is the cooling system really that bad or does it just come down to poor repair?

As an aside I'm about to put in 4.56 ratios which should reduce the load on the engine significantly.

Should also add I've had the XJ for 8 years and have put 120000 of those KM's on it with trips up to Port Douglas in Summer included in there etc.

Cheers
Steve