OK guys I humbly come to ask your advise. I have a 96 sport with the 4.0HO. It originally had a bit of an overheating problem when I bought it so I threw in a 3 row aluminum radiator and that took care of it. About two months ago we were up wheeling and I pushed it pretty hard trying to get over some snow banks. Anyway I got it home but every time I would go uphill or put any stress on the engine it would start to overheat. I never let it get into the red but it would have if I didn't take it easy.

So I figured I'd just go in there and do a basic overhaul of the cooling system. here is what I've done so far:

New t-stat
New upper/lower hoses
All new gaskets
Override switch for the stock e-fan
Converted mechanical fan to a tuarus electric two speed fan
Grand Cherokee alternator to accommodate the E-fan
New 2 row all aluminum radiator(had to go with the 2 row to fit the E-fan)
Cleaned out the A/C condenser to get max air flow
Tranny cooler
Pulled out the water pump and all the blades seemed to be in great shape and spins freely
Replaced the radiator cap about 5 months ago
Pulled the head off and inspected it for cracks
Replaced the head gasket
I have flushed the block a couple times and the heater works great so I don't think the heater core is pluged.
I also have properly burped the system

It definitely runs cooler, but it still slowly overheats when putting any stress on the engine. and this is with both e-fans running on high.

My thoughts... ? maybe the water pump/temp sender
I'm pretty baffled by it. What are your guy's thoughts?

 

You can easily be fooled with a visual inspection of the water pump.

I'd replace it with a new (never rebuilt) one. They aren't expensive.

If I pull a water pump out, a new one goes back in.......

 

Verified temps with infrared temp gun?

 

I did not verify the temp is there somewhere that will do this for you?
I tend to agree that it might be the water pump anyway to verify this?

 

Try a 165deg fail safe t stat and keep fan on non stop in the trails.

 

Anyone else have any thoughts?

 

Mainly curious, your shroud is in OK?

 

Yeah the shroud is in.

 

dont go with the fail safe when your having a overheating problem,always try changing the temp sensor you can be fooled by it,they tend to fail after a few years,and the reason for the fail safe t-stat is if its overheating it will stay open and you wont fix the problem like that,and never run under the temp. required, all 4.0 tend to run on the hot side,but get a regular 180 or 195 t-stat and your motor will do its cycle of opening and closing when temp is reached,i work on my xj all the time and ran in to that problem my self,but its common sense,you want to keep it at the right temp,so you think it out,if your runing a 165f t-stat when will it get to that temperature? after running the hell of your fans? so if you get a 180f,it will cool it faster and keep it there,also one big thing about when you change your radiator,always try to clear the head of any rust by running water thru it,but in the end my bet is on the temp sending unit...Good luck.

 

agreed, before spending any more money and brain power, verify the temp when it's "running hot".....my money is on the sending unit...I have also seen it happen from gasket sealer and pieces of gasket material clinging to the sensor because of left over or over excessive application of sealer when the t stat was changed.

 

Intresting thanks guys.

 

What are your signs of overheating, other than high gauge readings? I still think u should verify temp with a infrared point-n-shoot temp gun....there handy as a pocket on a shirt for all kinds of things temp related. As much as u have done/modded the cooling system (snow on the ground sounds like cool ambient temps), maybe your temp gauge is giving false readings.

T-stats do one thing, control minimum coolant temp. Ambient temp, condition of the cooling system, design of the cooling system (mainly front surface area of the rad) and driving conditions (load on motor) determine max coolant temps.

 

What octane fuel are you using?

As far as the T-stat, it's possible to have a bad one out of the box, but only if it was stuck closed would it cause the engine to get too hot. You can test this by completely eliminating the t-stat from the equation (if it's possible, forgive me, this is my first non-GM vehicle and I have yet to do any engine work on it).

It will take longer to reach operating temp this way, but if it continues to heat up to the point of overheating, well, you know the t-stat has NOTHING to do with it.



You need to know that the only thing the T-Stat does is restrict coolant flow while your engine warms up when you first start it. It constricts flow so that the coolant moves slower, therefore spends more time heating up before passing through the engine. Once the coolant reaches a certain temperature, the t-stat opens, allowing full-flow, which will keep the coolant at the operating temperature.

If your t-stat is NOT opening, the coolant will be moving slowly and heating up more.

Some t-stats are designed so that if they fail, they fail completely open, so it won't cause overheating - you'll notice that your vehicle takes a very long time to reach operating temperature.

You seem to have the opposite problem, which suggests a faulty t-stat, but might not have anything to do with your cooling system at all. Try what I suggested, removing the t-stat and running the vehicle until operating temp, then trying to recreate the conditions in which it overheats - if it does, there you go, get a new t-stat. If it does, you have another problem, and can put your t-stat back in.

EDIT: you can also test your t-stat by dropping it in a cup of water heated up to the temp the t-stat is designed for - say it's a 165 degree t-stat, heat up some water to 170 or 175 degrees and drop the t-stat in it. You can watch it open up when it heats up. If it doesn't, it's bad.

 

UPDATE...
Ok I replaced both the waterpump and the temp sender... and... same story slowly starts to overheat when putting stress on the engine.

I think I am going to try to take the thermostat out and see if i can get it to do the same thing or at least throw it in some hot water.

If that doesn't do it I might try to upgrade the wiring on the new e-fan, but that shouldn't make to much difference when going faster then 35 or so.

Any other ideas?

 

is it automatic and maybe the transmission is actually getting hot ttransfering heat to the coolant in the radiator,also partially plugged exhaust will also make engine run hotter from not allowing exhaust to escape fast enough???????????