Tranny Cooler

I have been having overheating issues and one of the things I have tried is disconnecting the in-radiator tranny cooler plumbing and installing an additional tranny cooler instead. It has the factory tow package so there is already a tranny cooler in the grill. My question is this, will the 2 tranny fluid coolers keep the fluid cool enough when the outside temp is 100+? My reasoning behind this mod is that the coolant temp runs 210 plus when it's hot outside so more heat should be removed from the fluid to the outside air. Additionally the trans fluid won't be adding heat to the coolant which should help with the overheating problem. Are my assumptions correct?

the external trans cooler is plumbed after the internal. adding an additional will only reduce trans temp slightly.
beyond that, you aren't going to accomplish much . oil to air heat exchangers are not as efficiant as oil to water heat exchangers. your trans will overheat quicker. if you put it before the radiator, the radiator will heat the fluid up to rad temp. IMHO you would be wasting money unless you were trying to cool the trans.
You need to find the problem with the engine. it should have no problems staying cool in temps upward of 110*
210 and up to about 235* is normal operating temp and you are ok. If it can't control itself and boils over, and you are certain that there are no underlying problems, the you need to have a larger radiator core .

Ive seen several high mileage 4.0s in my shop here in CO that do fine in cooler weather but overheat when the temp outside is hot or as they go up in altitude. The head gasket needed replacement. The smaller water ports in the headgasket get clogged or swollen with age and coolant neglect. That casues poor water flow around the cylinders and higher running temps.

You should also hear the thermal fan clutch when it is working... a definate increased roar to the engine... if not then it needs changed.

I still have overheating problems after doing the tranny cooler mod. After, replacing a new fan clutch, flowmaster water pump, radiator cap, 3 core radiator, tranny cooler mod, electric fan running 100%. I still heat up fairly quickly on going on an incline, I usually slow down to a crawl and it will cool down fairly quickly. If I have the a/c on it usually heats up fairly quickly.

What tests can I do to confirm that it is a headgasket problem? I know testing of the coolant is the best way but out here in MY its fairly difficult to get a test like that done.

Thanks

That sounds like a possible flow issue to me. I know that you've replaced alot of parts, including the radiator, but if the coolant isnt flowing through the block well, especially under load when the engine needs that flow the most, then you could very easily have that problem. The water jackets may be corroded or just crapped up and so it'll just hold the coolant in the block longer, making it hotter faster. Just a suggestion...

I have a 88 XJ and in 2000 I replaced the factory radiator, factory fan clutch, factory thermostat, factory heater hoses, factory heater hoses, pressure cap on pressure bottle all the result of a broken fan belt. I figured it was the factory fan belt with 115,000 miles on it.

You have not mentioned anything about the age of your XJ's components. Here some rules of thumb I have picked up over the years:
* Radiators - 7 years max life, anything more is just good luck
* Thermostatic fan clutch - no good way to test them, replace at 5 years of age
* Hoses - replace every 4 years regardless of mileage. Also make sure your lower raditor hoses has a spring inside, it can be sucked shut of the spring is not present and cause overheating. I use dealer radiator hoses, well made and have the anti chafe installed. I also use dealer heater hoses, no aftermarket store lists all 6 sections of heater hose.
* Thermostat and "radiator cap - I change every 4 years when I am changing hoses. I also use ONLY a dealer (Mopar) themostat. ONE overheat can damage both of thse items and I can confirm that.
* coolant - use distilled water to mix with coolant, also flush out the block with distilled. You do not want to add minerals to the cooling system to make your situation worse.

Your profile says you have a 1990 XJ, the plastic pressure bottle known for failing and not holding pressure. You can get a new one for $20 from www.quadratec.com and that includes the "cap".

It sounds like you to do a cooling system renewal - radiator, fan clutch, thermostat, pressure bottle & cap, and radiator hoses. Also if you do heater hoses, do them if you still have the aluminum bands at the wye ftting and heater control valve. Also if you change the heater hoses you can flush out the heater core.

When you install the new radiator hook back up the trans lines to the radaitor cooler. Your worry about overheating is a little unfounded, there "engineering" that went into sizing that Aux cooler also adding the second cooler will do essentialy nothing more to cool the ATF.

I also hope you have the owner's manual so you know how full to fill that pressure bottle.

Hi Buffalo Matt,

Thanks for your input, need to clarify a couple of things... What do you mean by water jackets being corroded and capped up? What are water jackets?

Thanks!

JungleXJ said:

Hi Buffalo Matt,

Thanks for your input, need to clarify a couple of things... What do you mean by water jackets being corroded and capped up? What are water jackets?

Thanks!

Click to expand...

A water jacket is the area around the cylinders and in the head where water flows.

The cylinder head gasket has several large and small holes where the water is directed and or restricted by design to cool the block and the head.

After many years the smaller holes can become restricted from deposits or the gasket itself becomes swollen or corroded away by aging coolant that has a bad Ph and closes off the smaller holes causing hot spots and slow water flow.

martin said:

I have a 88 XJ and in 2000 I replaced the factory radiator, factory fan clutch, factory thermostat, factory heater hoses, factory heater hoses, pressure cap on pressure bottle all the result of a broken fan belt. I figured it was the factory fan belt with 115,000 miles on it.

You have not mentioned anything about the age of your XJ's components. Here some rules of thumb I have picked up over the years:

Click to expand...

Martin, thank you for this excellent checklist. If you'll answer a few questions I'll print it out & keep it in my glovebox.

(1) Are you saying the parts you replaced in 2000 were the ORIG. '88 factory parts that were still good until they were destroyed by a broken fan belt? If so, why then do you now recommend changing these parts at such radically shorter intervals? (I won't relist them: refer. post #5) I think Eagle has said that anything beyond 10 (not 7) years on a radiator is sheer luck. Are you just erring on the safe side or do you think today's parts are inferior to the '88 era ones?

(2) Are all the "rules of thumb" you give applicable for a '96?

(3) What radiator do you favor when it's replacement time?

Where do I start, I did not own the 88 XJ until 2000. From 1994 to 2000 it was owned by my parents, it had over 90K when they purchased it. After my Dad passed away in 1997 the XJ found its way to my house since I lived closer to our 80 acres in the Missouri Ozarks.

It was not my vehicle until 2000. I was getting ready to move to Alabama from St Louis and had the fan belt break. That when I got my introduction to XJ mainteance. Then when I discovered how little maintenance had been done in the XJ.

It a personal opinion on 7 or 10 years, things like coolant maintenance influence those numbers. But 12 years or 15 is being risky....

My rules of thumb is what I use on all my vehicles, not just XJs. It is cheaper to buy parts and replace them when I have time than to wait for it to fail and add an urgent repair to my life. I am into paying for new parts to avoid "pain" later from going cheap and leaving me stranded.

In 2000 I installed a 3 row GDI, in 2004 I installed a 2 row modine. I found a leak in the GDI where the tank crimped onto the tubes. I figured it was easier to get a new one than to try to get a warranty repair. I use the auto shop on a military base and they charge by the hour you use the bay.

I went with Modine since I am familiar with them form work. I can't say the GDI was bad but saw posts on how GDI changed the part number for XJs since they had so many quality problems. I got the Modine for a good price, their is a Modine distributor in town and they had it in stock.

If you have the radiator out you be silly not to change out the fan belt with all that access. Also you may want to change the water pump, you have lots of room to do the work. Also the crankshaft damper/harmonic balancer fails around 100,000 miles, if you need to change the damper, with the radiator out it would be a good time also.

I hope that helps...

Digger87xj said:

A water jacket is the area around the cylinders and in the head where water flows.

The cylinder head gasket has several large and small holes where the water is directed and or restricted by design to cool the block and the head.

After many years the smaller holes can become restricted from deposits or the gasket itself becomes swollen or corroded away by aging coolant that has a bad Ph and closes off the smaller holes causing hot spots and slow water flow.

Click to expand...

How can I confirm that there is a restriction on the smaller holes? Is there any test I can do besides tearing it all apart. When I changed my thermostat and waterpump there was quite a bit of crud on the thermostat housing. The guy I bought the XJ from had it sitting around for more than a year.

Thanks

martin said:

It a personal opinion on 7 or 10 years, things like coolant maintenance influence those numbers. But 12 years or 15 is being risky....

My rules of thumb is what I use on all my vehicles, not just XJs. It is cheaper to buy parts and replace them when I have time than to wait for it to fail and add an urgent repair to my life. I am into paying for new parts to avoid "pain" later from going cheap and leaving me stranded.

I hope that helps...

Click to expand...

Yes, it helps. My '96 just turned 100000 miles & has no apparent problems of any kind; starts on a dime, clean exhaust, smooth idle,burns not a drop of oil, not a drop of anything leaking anywhere It was obviously beautifully maintained & gently driven, belts/seals had been recently checked/replaced, AC serviced/charged. I had the extensive 90000 mile scheduled maintenance done w/tranny flush, this fall a radiator flush (mechanic said the old coolant looked good w/no evidence of corrosion) & switched to Eagle's Castrol Syntech 5W 50 at my first oil change.

(When I had my recent brake job done I told the mechanic to go ahead and put in the new MOPAR thermostat I'd been carrying around for an emergency (having learned via about the little hole on the top that other t-stats don't have .

But when something gives--which will most likely be the radiator--I don't want to be penny-wise & pound-foolish. You're saying radiator replacement should include fan clutch/pressure bottle & cap/radiator hoses (and the hoses must have a spring; does that mean MOPAR only?). and that it's also a good time to replace water pump/fan belt/harmonic balancer. (I assume the harmonic balancer is the same thing as a crankshaft damper?)

Is that it? Speak now or forever hold your peace because I'm printing out this list. I'll look back at the best-radiator poll too. And which of the replacement parts should definitely be MOPAR? I want to make a note of that.

What might be the first sign of radiator failure, BTW?