Inked_Elliott

First of all hello everyone! So my '93 Grand Cherokee Laredo has been having some overheating issues in the summer for a while now. I have flushed the system, replaced the radiator, and replaced the water pump. I'm getting a pressurized return tank for it, and I'm going to check out the fan clutch. Beyond that it runs at about 210 on flat ground (with the heater on medium) in 80 degree weather. When I'm going up a steep grade or I get the RPM's over 2700 it starts to heat up, fast. I was wondering if you guys think that the transmission may not be getting adequately cooled, or if it's something else (like that tricky fan clutch).
I'm moving to the Vegas area next year and with 400k miles on this old girl I want to make sure she's not going to go belly up on me. I can't see a transmission cooler being a bad idea, but I'd love some input!

Thanks!

dave1123

I would think an aux trans cooler would be a good idea. Just make sure the hot trans fluid goes to the aux cooler FIRST before it goes to the rad cooler. You also might want to flush out the rad cooler to make sure there aren't any restrictions in it. You could also go with an electric fan to either add extra cooling or as the main source of cooling air. With that many miles on it, has the block ever been flushed? I mean chemically? One other thing. The 4.0 takes two different water pumps. One for the v-belt system, and one for the serpentine belt. They spin in opposite directions. Because the back of the pump is wide open, both will work, however the flow will be substantially different. Make sure you have the right one. You shouldn't have to have the heater on to keep it cool.

Inked_Elliott

The water pump is the right one. I quadruple checked that one. I replaced the cap on the coolant return tank and that made a world of difference. The old one was cracked and barely a cap any more. The engine temp is now holding at 210 beautifully, even uphill.
I am going to flush the system, had not thought about a chemical flush. What would you recommend for that?

dave1123

The one thing I've used is two guarts of CLR in straight water, run at normal temp for 30 minutes, drain and flush with water, add 1 cup of baking soda and run for 10 minutes. Flush and fill with coolant. Be sure to pull the block drain plugs and poke a screwdriver into them to remove the rust around the drain holes.

I've lived with well water for 20 years, so lime in the water tends to plug everything. The CLR or Limeaway breaks up the calcium deposits very well.

There are as many radiator flushes on the market as brands of oil. I used to use Dupont #7 which was a two part powder product, but I haven't seen that in a lot of years.

Inked_Elliott

Awesome! I'll have to give that a shot. Now I'm paranoid that I may have put the wrong water pump on My Jeep has the serpentine belt, and if I can't find markings on the existing pump I'm just going to replace it. Should the pump be reverse or not?
It's still getting warm (up around 240) at times while idling and such with the new overflow cap on it, but it cools back off nicely when we're moving. Going to put the new fan clutch on this weekend and see if that helps too, I'll be doing the clutch with the pump, no need to take it apart twice! I'll let ya know how it goes.

Thanks for your help, it's greatly appreciated

dave1123

When I replaced the one on my 97 ZJ, Napa had two part numbers. I looked at them both and the only difference I could see was the direction on the swirl of the impeller. I bought the one they listed for my serp belt. When I got home I took the old one off and compared them. I'd bought the right one.

Word of caution! Buy the premium pump with the metal impeller! The impeller spins about 1/16" from the first cylinder barrel and the plastic ones have been known to shatter when the bearing gets a little worn. Mine was so worn, you could move the fan about 1/2" and the cylinder barrel had a wear groove in it! I was amazed it wasn't leaking! Just noisy.

BTW, I've owned 2 4.0s and neither one EVER overheated. I never towed anything. Maybe I got lucky. The only time one got hot was because I didn't purge all the air out of the system on an antifreeze change. The temp guages stayed rock solid at 210* even pulling up a mountain on the highway.