I have a 2000 cherokee. I drove it yesterday with no problem and everything worked normal. Today I started my drive home (about 100 miles) and had no heat for the whole trip. About half way home I stopped for food and when I went to leave noticed i had coolant explode out of the cap that says "Dont open when hot". Its -5F out right now and it did not overheat. Any ideas on what happened and how I can fix it? Anybody know if its safe to drive home?

 

you lost ? some, why?
you can run and see where temp reads when hot.
id be very concerned.

 

I'd say it did over heat. Possible cracked head

 

Sounds like it overheated to me. Something over pressurized the cooling system. A cracked head is (now) very likely. Where was the gauge reading when she blew? If it was reading 210 (that is normal operating temperature) when she blew, the coolant sensor is shot. You see 210, but the coolant could in fact have been boiling. Did the electric fan kick on? I think it comes on at around 215 or so. Both the waterpump and thermostat are suspect as well.

I would not drive it until the culprit is found or you could wipe the bearings out with coolant. Not worth the risk imo.

 

It was -5 F and it overheated? What would cause a vehicle to overheat when it's that cold out?

 

Check the oil on the dipstick and see if you can any water mixed in with the oil.


Check the thermostat and radiator cap both it may be bad, just to many different things it could be, you need to do a bunch of checking till you find it.

 

"It was -5 F and it overheated? What would cause a vehicle to overheat when it's that cold out?"
Frozen "coolant".

 

What turbo said.
Your coolant wasn't up to the cold temps, and your radiator or upper hose froze and blocked. First thing you should think of when the heat doesn't work in the cold weather.

 

Bad coolant. Whether it was old, watered down, low or what, having bad coolant caused the system to freeze up. No coolant was moving through your heater core, and if it wasn't moving at ALL through the engine, you might have a problem. Vehicles can overheat and NOT crack heads contrary to popular belief, but if you drove it with no coolant, a big air pocket in it, etc., you COULD have burned up the head gasket. Start by checking how much coolant is in there, fill it up and burp it good and go from there. The cooling system is pretty straight forward and easy to work on in our Jeeps.

 

Hey may have the 0331 head which is more prone to cracking. The likelihood that it did crack is high if it is the 0331

 

Could be, but no sense jumping to worse case scenario right out of the gate.

 

I'll give the peep credit for driving that thang in -5°F with no heat, **** that noiz.

 

There's a pretty good chance that heat from the engine thawed out the frozen section of your cooling system after you stopped (and air flow stopped). Once the frozen section of your cooling system thawed, the superheated coolant had a chance to expand into the area of the fill cap, and it was no doubt higher pressure than your radiator cap rating. It doesn't mean you cracked the head or blew a gasket, but it's possible.

For future reference, frozen cooling systems are usually discovered by the vehicle overheating. I know it seems strange, but water cooled engines need water to flow through them to remain at operating temperature. Air on the outside surface of an engine doesn't really do much cooling of the internal mass of an engine.

 

Yes of course it doesn't mean he cracked or blew anything. But its free to do some tests to check.

 

Yep. Free tests should be done.