More overheating.. Cont. from last summer

My 96 4.0, AW4 is overheating only when under a load.
I think I've tried everyting my wallet and I can possibly think of.

Here's a list:
GDI 3 row radiator
Hesco water pump
Turbo City switch kit for aux fan
Turbo City t-stat housing
Fan Clutches (note Plural, many times over)
Numerous thermostats, 160* to 195* OEM
Water Wetter
Hood Vents
New Hoses, Rad & Heater
New Pressure Cap
Pressure tested everything
New cap, plugs and rotor
New serpentine belt
Tried different coolant mixtures
new heater control valve
new temp sending unit
and probably a few other things I cant think of right now

Runs just below 210* around town, idling, etc but when on the highway pulling a grade, it climbs up to just before the red zone and stays there until I get to the down hill.

Thanks for any input or ideas you guys may have

Dan (completely frustrated) Turner

Dan,

It's just a possibility, but consider the following: Where does most of the heat from the engine dissipate from? The answer is NOT the radiator.
Most of the heat coming out of the engine is expelled through the exhaust. If your cat or muffler are not working properly then the engine might be overheating.

If that doesn't work, you can move to Colorado - it's cooler here.

LOL, I had my exhaust guy test exhaust flow. He drilled a small hole just before the cat, had me hold it at like 3000 rpm and put some kind of doo dad in the hole to measure flow.

He said it only had like 3lbs or something. But concluded it had no restrictions.

Just want to beat it with a BFH>

Thanks, Dan

Maybe you have thought of this but could the water pump be one designed for the older fan belt setup, say for a wrangler 4.2 rather than your 4.0? It might fit, but the impeller would spin backwards. The serpentine belt system is reverse rotation.
Also, how does your trans. oil look? Check the trans cooler lines for road damage and the cooler hoses for kinks.

Dan,

As an experiment take out the thermostat and see how it runs. If it gets just as hot that tells you stuff, if it does not get hot it also tells you things.

You may want to check out the lower radiator hose, some came with a spring inside to prevent it from being sucked shut by the water pump. With that Hesco pump you may have a larger vacuum pulled on that hose and causing it to close off. When you changed the lower radiator hose did you swap the internal spring? Why not call the dealer and ask what a hose runs and if they show a spring for the inside. If you don't have a lower radiator hose with a spring go buy the spring or spring & hose and install it.

You may want to take you radiator cap to a garage and have them test it to make sure it is holding pressure.

When you filled then engine with coolant did you remove the coolant temp sensor in the head so the air could get out? Even with your changes of coolant you may have an air bubble in the engine.

Have you verified if the electric fan is working and I don't mean your manual switch? On my 88 XJ the fan comes on when the AC clutch is engaged.

I know on fan clutches there is clockwise and counter clockwise clutches. I installed a carquest clutch on my 88 XJ and it has worked great! The OEM clutch I removed was AC/Delco. Where are you getting your clutches?

Martin

The last time i ran into this the customer had a cracked head. and the block was plugged up with "debris" i replaced the head and sent the block out to be vatted. also the trans could be over heating causing excess heat to go into the radiator via the trans cooler. these are about all i see left that has not been done and that i've seen before. to test the trans install an aux. cooler and take it out of the radiator. see if the o-heat goes away. if not pull a rear freeze plug and take a look.

Not sure about the spring in the lower hose, I had a friend helping me this weekend and he put that hose on. I have a pressure tester, and everything checked out good. I verified that the pump is rotating the correct direction as well as the fan clutch. When the t-stat housing and water pump were off, the water jackets looked spanking clean. The trannie is bypassed from the radiator.

Can you see my frustration??

Thanks for the input, keep it coming.

Dan

BTW, I did bleed the air out of the system, first with the pressure tester, and then by the temp sender, then let it run with the cap off for quite a while with the front driver's side jacked up to make it the highest point.

Dan

Do you have AC, did you check the condenser.evaporator that is in front of the radiator. If that is blocked with debris, bent fins, etc it could be restricting air flow. Also where did you put the hood vents, if you put them back near the windshield then you put them in a high pressure zone which can prevent hot air from escaping vs near the nose where you would draw low pressure and the hot air would be sucked out. About the only way I can think to check this is to get or borrow a beckman or simpson vtvm and a remote temp sensor to stick in the engine compartment so see if hiway speed has any affect on the engine compartment temp. I'm really pulling at straws here. I hate to say it after you have invested all this money and time but I've never been impressed by any of the aftermarket stuff like the water pumps, tstat housings, etc. The high performance water pumps may move more water but unless your radiator is capable of flowing that increased volume of water all that pump is going to do is churn the coolant maybe even aerate it.

Rich, The AC condenser is clear, and the hood vents are at the front of the hood. I think it may be time to buy a baja bug so I don't have to worry about the cooling system any more.

thanks, Dan

How did you verify that the water pump is rotating in the correct direction? Direction of rotation isn't the issue -- unless you put the serp belt on wrong, it can only go one way. The issue is that the older 4.2L engines with conventional vee belts have a water pump that is externally identical and will bolt onto a 4.0L, but the vee belt setup rotates the opposite way so the impeller blades are oriented "in reverse." Only way to check is to remove the water pump and compare with one you know is for the 4.0L with the serpentine belt.

A friend of mine had the lower hose problem that Martin referred to. In fact, his hose had a spring inside, but the spring wasn't long enough. He finally went to a radiator shop and they let him scrounge through the trash barrel, where he found a couple of extra springs in the correct diameter. He put one of those in the lower hose to extend the one already there, and the problem went away.

I don't know how exhaust pressures are read, but I know that my exhaust pushes more then 3 lbs of pressure, but thats jsut testing by pushing my shoe over the tailpipe.

Eagle, when I changed pumps, I verified with the original oem pump that the impellers were going the same direction. I checked a while ago ( squeezed the radiator hose) and it is inseed lacking the internal spring. Sent Pops down to the dealership to get me a new oem hose. We'll see tonight.
I have to drive it to Phoenix, AZ in two weeks, so it's gotta get fixed. Thanks for all of your input,

Dan

The exhaust pressure was tested before the cat. I guess if there was any blockage in the cat or muffler it would create high pressure upstream of the blockage. That is how I understood it, feel free to set me straight if I've got it wrong.

Dan

It's a long shot, but maybe the temp gage is bad.

....

I also thought that a blown head gasket would cause overheating.

I just got over this exact same problem. Normal running, idle, temp stayed right at 210. Hit the highway, pull a few hills, and it was coolant puke city. Turns out, I had a cracked head. Compression test showed equal on all cylinders and within limits. However, it was tested cold, and I never did a leak down test. When the engine warmed up, the head expanded, the cracks opened up and combustion gas entered the coolant, and coolant exited the exhaust. I finally pulled the head out of frustration and volia, there it was, stearing right at me. Now the one my EX overheated while I was in Iraq. Well it has a cracked block, broken exhaust valve, multiple cracked head, and a hole in the number 1 piston you can stick both thumbs through. Two engines within 20000 miles, and getting ready for the third. Now I know why it means Just Emptied Every Pocket.

A new OEM lower radiator hose comes with a spring inside to prevent it from collapsing under the negative pressure induced by the water pump pulling coolant. If your hose is old, the spring has probably rotted away so it won't be doing its job.
The Hesco water pump is designed for the 4.0 so it's reverse rotation like the OEM pump, therefore the water pump isn't an issue here.
It sounds like the exhaust guy checked the backpressure in the exhaust to see if the cat was plugged. A result of 3psi is within spec so that rules out the plugged cat theory.
The '91+ 4.0 has an open cooling system that's "self-burping" so air in the cooling system shouldn't be an issue. Driving uphill will certainly expel any air that might be trapped.
One thing nobody's thought of is the possibility that the engine's running too lean. That would certainly make the engine run hot and detonate under load. How old are the injectors?

Wow, thread brought back from the dead, but it still haunts me some.

Dr Dyno, The injectors are the originals as far as I know. I know you've done a lot of research on injectors, what would you reccommend for an upgrade on my 96??

Maybe the fact that I have built a tank out of my XJ (Bumpers, Roll cage, big heavy tires, lots o' armor, etc.) it just has to work a lot harder.

Dunno.