Heater, Fan, Overheating

90 Cherokee 4.0L

(Searched and couldn't find this combo of issues.)

Girlfriend called panicked, Jeep overheated today and most of the coolant steamed out. After it cooled down, I put more coolant in, cranked it up and let it run with the cap off the bottle and it immediately started gurgling and bubbling but didn't seem to be hot yet. Turned on the heater, drove it a little. Coolant was not leaking, but it overheated again very quickly and the heater never started blowing hot. It was about 50 degrees outside and the heater was blowing cool air and never warmed up. Then I noticed the small electric fan was not blowing. Is that always supposed to be on or just when hot? Replaced t-stat with a cheap one a couple of years ago.

Limited money, limited time. What should i do first? Thanks, guys.

Sound like the cheap thermostat is haunting you again!!! I would change it out again, and go from there. A easy way to see if the thermostat is opening and closing is grab the upper and lower radiator hoses, and see if they are the same temp, if one is cold, and the other is hot, then i would say the thermostat is stuck closed.

maybe thermostat was cause of initial overheat condition. after fixing that, be sure to burp it. If not burped, it will exhibit exactly the symptoms you described (gurgling, overheating on the gauge, no heat at the heater, etc.).

I remember installing that t-stat and it was small compared to the housing that bolted in. I remember having a hard time figuring out how to keep it in place while I screwed the bolt in. Maybe I am an idiot, but how do I hold it in place?

The Renix plumbing design is flawed, and tends to leave the top of the radiator 1/2 full of air for months and thus useless at cooling.

If the radiator is partly clogged (tubes scaled up) the flow is too slow to get the E-Fan switch hot enough to turn on the e-fan.

Pull the top and lower radiator hoses, and duct tape a garden hose to the inlet, and see if you the radiator flow is good, or restricted (turn on the garden hose water slowly). Then reverse the garden hose and back flush the radiator to see if some tubes will unclog (you might try the back flush FIRST!!). Be careful not to over pressure the radiator with the garden hose!!!!! City water is as high as 70 + PSI, radiators are only run at 16-20 psi max.

Pull the T-stat and see if the over heat froze it open or closed. Test the replacement T-stat in boiling water (and the old one? to see if it was bad), as many new ones seem to bad out of the box these days (china).

If all is well, consider filling the radiator first, by disconnecting the heater core hoses at the T-stat - water pump connections to vent air while filling the radiator first. Then quickly reconnect the upper hose to the T-stat tube, and then complete the filling via the bottle, cap off while running the engine.

Then check the lower hose to see if it is getting hot to confirm coolant flow!!!!

J33PsRock said:

I remember installing that t-stat and it was small compared to the housing that bolted in. I remember having a hard time figuring out how to keep it in place while I screwed the bolt in. Maybe I am an idiot, but how do I hold it in place?

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Make sure the T-stat was not upside down or the wrong part. It is also good to make sure it has a giggle valve, or add an air purge hole if does not have one!!!!

Many people are only using dealer T-stats lately.

Thanks, guys. I'll be hitting this first thing in the a.m. Just got it home.