I have a 90 Wrangler with the 4.2 I6, and my problem is :when I shift into 5th gear the temp. creeps up and tries to overheat, but if I shift back into 4th the needle goes back towards the cool side.I'm running 31x10.50x15 Baja Claws, so I don't think tire size is a factor.I've heard of the same problem in a CJ7 with 33's but he couldn't figure out the problem either.Any help would be appreciated.Newtron

Well it would be nice to get a little more info....such as if it seems to be directly related to engine rpm.

But, from the detailed info, I am pleased to say I know exactly what the problem is.

Your cooling system.

I would suggest replacing.













Okay, at least I think I'm funny. Anyways, from here you'll need to narrow it down some. Have you had any coolant leaks? Is your radiator currently full? What is the condition of your fan clutch, and what does the temp do in traffic? Is the radiator blocked by anything, such as a big bumper or a winch?

One other thing....how does your heater work? On jeep 4.2's, the coolant temp sensor is in the intake manifold, which is heated by coolant before it enters the heater core. If your heater core is partial clogged, then this water will be forced to stay in the intake....where it will heat up due to the exhaust manifold immediately underneath. When the engine is at a higher rpm there is more water pressure, and this "super heated" water would be forced through the heater. To check for this problem, simply bypass the heater core.

Good luck.
-Jordan

Have you radiator checked for being clogged, its pretty cheap

sounds like a fan clutch issue, engine RPMS goes down and the fan isnt spinning fast enough..

Either that or water pump

Originally posted by WheelingPiazza
sounds like a fan clutch issue, engine RPMS goes down and the fan isnt spinning fast enough..

Either that or water pump In 5th gear, he does not need the fan Steve.......I'd lean more towards the water pump.

Tries to overheat, or overheats?
How hot does it get?
What temp. thermostat are you running?
Are you sure of the accuracy of your temp. gauge?

If the temp. rises, but stops rising at or about the opening temp. of the thermostat, might not be anything to worry about.

If you actually do have an overheating problem, it'll take some more information to give you anything better than a guess. There are many variables to consider.