Hey all. I am trying to fix My girls 99 grand cherokee 4.0. We had 20 below temps and I thought it froze up.. but not its been 40 plus for a few days and it will stick at 210..if I leave heater off. turn it on and it climbs like a rocket to way too hot...shut it down..and now I cant figure this out. We have a snow storm on the way at midnight and I need Help...Please.. Peace


It has 200,000 Miles on...

 

Fan(s) working OK?

 

He says that it sounds like the hobbit that turns the crankcase is depressed and needs therapy. We need to get us a new hobbit. They's from the land beyond time. Land beyond time's also gonna hook us up with the unicorn for the radiator. I ain't even gonna tell you about that haunted air conditioner. Plus the air filter, that's made of plutonium. That's gonna involve Superman, so, y'know, plus shipping from Krypton. Then the cow jumped over the moon.

jk for smiles

as stated in the post above, do both fans work, electric fan and mechanical fan clutch?
are you full on coolant? what kind (color) and is it mixed properly?
what is the condition of the coolant, clear, merky.....?
any foggy windows?
how is the oil level good/ bad?
can you notice anything wrong with the vehicle once the temp climbs or does the gauge rising become the only issue?

is anything boiling if the gauge shows too hot?
how old is the thermostat?

there are two hoses going along the top of the passenger side engine, are these hot with the heat on?

 

I kinda think he didn't like your humor.

 

IMO: I think your T-Stat may be stuck in the closed position. A series of gentle taps on the housing with the (plastic or wood) handle of a screwdriver might, I said might, free it enough to "pop" open and let the coolant flow. Even if that does work for you, this is only a diagnostic "cheater" step and a temporary solution, you still will need to replace the T-Stat. NOTE: Never tap the tool handle against the T-Stat housing harder than you would tap it against the bridge of your own nose (and don't try it on your nose anyway because you will see stars and make your eyes water).

Sorry to say this but other possibilities (due to freezing) include cylinder head cracked or head gasket compromised.

 

Those 2 heater hoses should be hot all the time. The heater is a full-flow heater core and acts like a thermostat bypass.

 

He never saw it, and hasn't been back to the forum not long after his post. Typical newb that wastes our time.

 

Actually, mostly impatient.

 

Raised on instant gratification, can't/won't devote time to learn on their own and have little-to-no appreciation for any dialogue that prompts thinking for oneself.

Rethinking my original response...

Regardless of whether they ever read it again, our unappreciative OP described "sticks at 210" with it OFF and overheating with it ON. Wouldn't that mean the heater plumbing is either breached or air-bound??

 

IDK man... it doesn't seem logical to me. Why would it overheat with the heater on. If it was plugged, it would get hot until the thermo opened. The heater is a constant flowpath for coolant at all times, even in the summer.

Anyhow, I'm not going to lose any sleep about it.

 

I haven't read of it happening here, but what if new guys gf has a bunch of stop leak poured into the coolant? Is that enough to ruin/ trouble a system...

 

Enough stopleak can plug radiator cores, but then it would overheat all the time.