Another 89 overheating, Confusion Inside!

First time poster so hi guys! With that being said I have scoured every posting on every website about overheating closed system cherokee's. I think I've gotten myself a little over informed. So let me tell you my situation.

I have an 89 cherokee with 200k on the clock. My over heating problem started about 1.5 years ago. I worked at a Ford dealership at the time. Ok so anyway, I replaced Thermostat, housing, water pump at this time, and also checked the e fan to make sure it was coming on. I also wired a toggle inside for said fan.

I left that job and moved back home to the hills of eastern ky...jeep was still overheating. Found the radiator was basically rotten. I replaced it with a stock 2 row aluminum job. Jeep ran great. No problems. Right around 200-210 mark.

Ok fast forward a few months and I made the grave mistake of letting my friend borrow my jeep one night. He ran it low on coolant, overheated it and blew the upper radiator hose. I replaced that and have had an overheating problem ever since. I found the reason that my jeep ran low on coolant that night was a pinhole in the reservoir, so I replaced that with a new one. Obviously, she still over heats, so on to the symptoms.

Jeep will idle fine without overheating. I can drive all day on flat curvy backroads. The minute I climb a hill, highway speeds or slow speeds the temperature climbs. When I come back down to regular grade roads, it slowly cools back down. The E fan is working the whole time. Although I spend zero time in stop and go traffic, I'm fairly certain it would heat up then as well.

Another issue is that when you first drive it...I mean waaay before it should reach normal operating temperature, it will climb all the way to 230-240ish temp on the guage...then abruptly drop rapidly back down to around 170 and slowly climb to 210 where it will stay. Thermostat opening?

Now on to my questions. Could an air bubble be causing this problem? I never really bled the system when I replaced the radiator hose or the reservoir. Obviously I keep adding coolant to it maybe once a week or so. Stupid on my part I know lol. It was bled when the radiator was replaced however.

I have read all the stuff on converting to an open system and have read all of Ecomike's posts on his setup and keeping the closed system. I don't have a lot of money to throw at it and since the radiator is new, don't really want to replace that.

I'm supposing I should start by trying to burp this system and go from there. Just looking for pointers from you knowledgeable guys. Thanks!

Burp the radiator, the top half may be half full of air. If the top half of the drivers side of the radiator is 50 F cooler than the bottom half, it has air in it!!!

Try a dealer T-Stat. The rest seem to be junk now.

Check for an exhaust leak blowing on the block.

Check the spark plugs color, and the O2 sensor live with an analog volt meter if you have one, to see if it is running lean.

Check the temps with an IR gauge, to verify it is actually running hot.

And don't throw money at it, Jeeps are like woman, they consume endless amounts of $$$s if you let them! :cheers:

I think I'm gonna start with burping it and go from there. I know I have an exhaust leak, you can hear, but that's been there from day 1. I'm hoping its just the air in the system.

I'm actually debating doing a setup like you have Mike, with the inline rad cap and volvo slant cap on the closed system.

I haven't put an IR gun on it but I know it is heating up. Can smell coolant and just feels hot..probably get what I'm saying.

The T stat is an aftermarket cheapie, not a dealer one. It only heats up under load..normal driving, even in these outrageous temps lately, it doesn't even flinch on the temp gauge. Just climbing a hill at highway speed and I assume stop and go.

Replace the crappy chinese cap on your reservoir with a 703-1396 cap from Napa.
As Mike says also, the aftermarket stats all seem to be junk anymore.

T-stat may not be allowing enough flow.

The exhaust leak may have gotten worse, and may be the tipping point while climbing a hill, as heat rises, and while climbing a hill the heat wants to go up hill, cross current to the fan flow direction, so fix the exhaust leak leak first, and your problem may be solved.

Ok guys. Thanks for the advice. Gonna do some things and see what happens.

Sounds like your bottle cap is letting pressure out when it gets to operating temp. and that stupid OEM style plastic tank starts to expand.

Also, like other replies have stated that the t-stat is sticking and probably not opening fully.