Two Problems

I have a 90 XJ with the 4 liter.

Alright first of all, I just did the thermostat in my truck, except I didnt put one in so it runs cooler. It still has an overheating problem. Are there any places I should start looking first? I've been told its the water pump, but I'm positive that it works since the first time I did the thermostat the gasket gave and it was blowing coolant everywhere within seconds.

Second is a little more serious. One of my mounts for the lower control arms, on the driver side, completely busted off the axle due to rust. The truck wanders and the dive when braking is almost unbelievable. Any suggestions on how to fix this? I had just planned to weld a couple of plates to the axle and drill some holes. If I were to go that route, how would I make sure the axle is centered? Would it be alright to measure center to center of the rims on the passenger side, then make sure the measurements the same for the driver side?

Vanquish said:

I have a 90 XJ with the 4 liter.

Alright first of all, I just did the thermostat in my truck, except I didnt put one in so it runs cooler. It still has an overheating problem. Are there any places I should start looking first? I've been told its the water pump, but I'm positive that it works since the first time I did the thermostat the gasket gave and it was blowing coolant everywhere within seconds.

Click to expand...

Need some more information. Is this an open or closed type system? Does it overheat going down the road or? Does the secondary fan come on? There can be several situations causing this situation.

Also, without any thermostat at all can cause the fluid to flow through so fast there is minimal temperature transfer.

If you have the closed coolant system(no cap on the radiator) the system is probably not filled correctly. In order to fill this system I have found it best to vacuum the coolant system down, make sure that it holds vacuum, and then refill it 50/50 mix. Best of luck. Randy

Not all of us have access to a vacuum machine...

If you think you're having trouble filling the RENIX block, and you aren't running a thermostat (I have an 88 that really doesn't like having one...) then just pull the upper hose off of the thermostat housing, and slowly pour coolant in there until the block is filled. Reattach the upper hose and finish filling at the football.

Still, you shouldn't have trouble with air pockets with no thermostat - have you flushed the system recently? Has it been flushed recently, if you haven't? How old is the radiator? RENIX radiators usually last 140-180Kmiles (reference: Jeep techs) and will want to be replaced after that. I've had good service from Modine and Performance Radiator, and those two brands you can usually find locally for good prices.

On the second - good question? I've not had to deal with that yet, but I'm sure someone else here with more experience than myself will chime in...

As far as the earlier comment about fluid flow without a thermostat - essentially true, but not much of an issue (I run around 195-200 w/o a thermostat in my 88. It overheats every damn time I put one it, and I know I'm doing everything right!) Besides, the operating temperature of the AMC242 is a little high, and I've run mine depressed a good 20 degrees for years without any ill effects, or negative impact on tailpipe emissions or fuel mileage. Just to let you know.

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I have the closed system. I also have not flushed the system out yet.

Also, the truck doesnt show any signs of overheating until the truck is off, which leads me to believe the theory of having no thermostat is bad, not enough heat transfer. Maybe when I shut it off all of the heat THEN gets transfered and just looks like it's over heating, but in fact just all of the coolant getting hot at the same time?

what do you mean it only seems to overheat when turned off? what is it doing when you turn it off?

It's rare, but I've run across about three engines that didn't like having thermostats in the last 25 years - the others were a Honda CVCC (1.8L in a 1980 Accord) and a Chevvy 2.0L I4 (85 Cavalier.)

They'll work fine - until you put a thermostat in. The only real difference you'll note will be that they take longer to get to operating temperature - but run fine anyhow.

In your case, I'd definitely flush the system (use something strong, if you have access) then change the thermostat and hoses after you rinse everything out. Make sure you fill up with coolant and distilled or R/O filtered water - if you use tap water, you're going to be in for a whole new batch of problems!

Heat transfer is heat transfer - and you'll actually have a little less heat to transfer with the engine off, even if it transfers more slowly (you aren't making any more heat, but all coolant flow is now by convection, which is slower.)

Start with a good strong flush, and see what happens after that. If you decide to install a thermostat, drill two 1/16" holes in the flange, 180 degrees apart, and where they won't be covered by the gasket. Install with one hole dead UP and the other dead DOWN, and that should help with not getting air pockets trapped in the block (works for me on the other three...) Let us know what happens after all that.

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