cooling system, where do i look next.

So ever since I rebuilt my motor I just cant seem to dial in my cooling system properly. 89 cherokee with 4.0 closed cooling. I Know I know I should just go open cooling and walk away but i want to dial this closed POS system in right so I know I fixed the problem. I was having over heating problems due to my bottle before and it not sealing up so I dropped in a intrepid bottle which solved that problem. I have a 180 thermostat some hoses are new and new water pump. I now run at around 150-160 most the time but it will jump up to and above 210 while wheeling. JUst cant seem to get it running at the right temperature and it has definitly been hurting gas mileage and during the cold weather has left me cold with no heat. Plus my engine isnt running at its normal operating tempature. Ideas where I should look next or say F it and go open?

I was having same problems. When i got my 90. From the 1st owner 70,000miles. and in the last ten years only driven 10,000miles. I thought everything would be good. But on the way home it would get hot at idle and along a steep grade, 210 and beyond. I new it wasnt the water pump. Its brand new. He had it done. So i put in a new thermostat from the dealer. So after i put it in Still did the same thing at idle and traffic the temp would just climb. So Looked at the rad it had the original. Mine has the factory tow package so heavy duty cooling system. So bought a 2 row and put it in. Looking at the old one all the rows were clogged. I also threw a new clutch fan while i was in there. So after burping the cooling system a couple times i got all the air. Driving a week all was good. People have always bad mouthed the closed system but when its in working order its great. So now most of the time its below 210. When idling or in traffic when the temp gets to 220 about a needle past 210 the electric fan kicks and the temp comes right down. I thought that was neat a closed system working correctly!! Who would have thought. Again people say the fan sensor is in a bad spot dont think so. Its been said here a lower thermostat will not lower your temp, True the 4.0 needs a 195. Dosnt matter were you live even in the high desert were i am if all your cooling system parts are working correctly then you will not have a cooling system problem.



Sorry for how long but this has been my cooling system story.
Anybody that has owned a cherokee has there own too.

Well, you have the right general idea. You must find and fix the issue. Switching to an open system only correctly overheating because you generally change out the bad part during the conversion. My '88 also remains closed and it runs less than 210 except on the hottest SoCal days and even then stops at 220ish when the efan kicks in. OK, enough of that.

First, you need to replace the thermo and go back to 195. It's way too cold outside to allow the engine to get to full temp when there's a lot of air flowing through the rad.

I'd try to verify the temps using an IR thermometer just to make sure your sensor's reasonably accurate.

You should flush and backflush the rad, the heater core, and the heater valve. When idling at full temp, feel the 2 heater hoses. Are they both hot?

Awww your killing me, another thermostat......I need to to go back to 195 I know. The cast on the block is getting warn down so getting a good seal from the thermostat housing isnt always easy. Guess thats what fine sand paper is for. I will also check hoses and I guess replace radiator, that was the step I didnt want to havbe to give into since it is about the same price to replace and switch to open.

good coolant flow through both heater hoses and nice and warm. Upper rad hose was cool but thats expected since thermostat isnt opening since im running at 160.

Unless there's something else wrong with it, there likely no need to replace the rad. A blocked rad would make it overheat, not "underheat". It would underheat if the thermo was stuck open.

It's hard to believe the temps are that low if the thermo is really closed given the sensor is at the back of the head. Can you get some kind of thermometer to measure some temps? I bought a cheapo IR one for about $40. Seems reasonably accurate.

For the record, there's nothing wrong with swapping out the closed for open system if that's what you want to do. Too many people think their overheating problem is because it's a closed system, and not because some component has gone bad.

i had it up at 230-240ish a couple times before I replaced the coolant bottle when I was trying to figure out what the problem was, can that generally mess up a thermostat???

whats the intrepid bottle and where can i find one?

out of a dodge intrepid. and at a junkyard or at a dodge dealer.

T-stats can outlast the vehicle they are installed in, but they can also go out in a matter of days/weeks for no apparent reason. At least they're relatively cheap and easy to replace.
I second going back to a 195* and finding what else is wrong.

Since this thread got brought back I will comment that I did throw a 195 back in. I run at around 210 but it still has been fairly cold outside. I have noticed my heat never gets as hot as it should so I think my heater core may be partially clogged, also making my coolant flow suck as well. I am gonna flush it here hopefully soon and see if this helps when outside temps heat up.

Hi everybody. I'm new here. I just inherited my wifes 89, and the cooling issue is of great interest to me. In Sept. when she bought it ti had about 200,000 on the clock and ran pretty good. She bought it because she needed a cheap tough mail delivery rig. A few weeks after she got it she said it got up to about 220 or 230 and smelled really hot. Installed a 180 or maybe a 160 (can't recall) and now it never gets over 220. The problem now is that heat only comes out of the defrost vents and it's not that warm. Also on my wifes new 01 whenever the efan kicks on it causes the whole rig to vibrate. So if any of you guys have some advice, it would be apreciated.

Don't use a low thermostat - it runs the injection rich, wastes gas, and doesn't fix the real problem.

The older Jeep probably needs a flush, also check the sensor actually kicks the e-fan on. The defrost only working tells you that vacuum to the flaps isn't moving them around to the heat position. Check all the vac hoses and listen that the flaps move around when changing the control.

On the 01, the e-fan vibration may be from the fan - loose, blade missing, etc. . Check if the A/C kicks in and if that is actually causing the problem.

are you sure your just not airlocked?

plymatt65 said:

Hi everybody. I'm new here. . . . . The problem now is that heat only comes out of the defrost vents and it's not that warm.

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Welcome to . My '89 had the same problems. Vacuum bottle (behind the front bumper) was bad and you need vac. to operate the heater valve on the heater hose under the hood. Also on mine there was a hose clamp end interfering with the heat valve movement.

Hey guys, thanks for the input. I am used to dealing with cooling systems in 60's mopars. The closed system in the 89 is a new beast to me. I will begin to look over the vac system and check the vac bottle. In fact the Jeep had some repaired damage to the right front corner when I bought it . What should I look for in a used bottle? The local Pick a Part has several Jeeps with bottles.

What is the best way, and or the easiest way to flush the cooling system?