I drained the coolant on a 4.0 grand cherokee. Removed the thermostat housing and replaced the gasket and installed a new thermostat and then the housing. Put everything back together. Filled up the radiator with a gal of coolant and a gallon of water. Took it for a test drive, parked back in the driveway, and saw coolant boiling out of reservoir, and from the radiator cap. Temp gauge is all the way up. Is the radiator too full?

 

*It'd be hard to 'overfill' the radiator. As the coolant heats up it expands and any overflow goes into the reservoir, which should have a 'full' mark on it. Full meaning with engine at operating temperature. As the engine cools, the coolant is sucked back into the radiator the same way it came out. Make sure your radiator cap is completely on and tight.. not in the 1/2 way position. That should be the only way coolant could come out there cause the cap 'seals' above the vent. Of course if the reservoir is too full, it will surely overflow. But out the reservoir cap, not the radiator cap.
*Are you 100% sure the business end of the thermostat is facing the block? That could cause it to not open and overflow when the engine gets hot. If it IS correct, a faulty new thermostat is not unheard of. I always throw 'em in a pot of boiling water to make sure they work.
*Another thing to check is that the lower radiator hose isn't collapsing. Hope you figure it out.. the 4.0 loves to blow head gaskets if you get 'em too hot.

 

Did you burp it?? Air trapped in the block/head can cause this.

 

I am almost positive the spring is going into the block...I can feel hot coolant in the hose once the engine heats up so I think the thermostat is opening..I didn't burp it before I drove it...I turned the heater on though. Coolant was boiling in the reservoir, the cap popped.offx, and coolant was coming outta the radiator cap. I don't think it was half.on.

 

Ok I checked the coolant level this morning and started the engine. I felt the top hose coming out of the thermostat housing and it got warm after a while so that means the thermostat is opening right?

But then the temp gauge started rising and i had to shut it off before it got too hot.


Any ideas?

 

I'd probably remove the thermostat or put the old one back in and see what happens. If the thermostat is open, the hose should be too hot to hold as your car overheats. I would think the hose would become warm just due to proximity to the hot motor. If the thermostat is closed, the boiling water would back flow through the radiator, as you are experiencing. I'd focus on the thermostat.

just my thoughts, good luck
Tom

 

You probably had a large air pocket in the head. Bleed it off by removing the temp sensor on the thermostat housing.

 

A+++ It will eventually burp itself through the overflow reservoir but you could damage the motor waiting for that to happen. Remove coolant sensor and top off radiator until coolant flows freely from sensor location. Re-install sensor,leave radiator cap loose, start engine and run at idle until thermostat opens and then immediately tighten cap. Do not remove radiator cap again,let engine cool and note how much reservoir drops. Add more coolant to fill line in reservoir. Check reservoir (when engine is cold) for the next several days and add coolant as needed.

 

Ok thanks all. I cranked it up last night after purging the air. Now my question is....the temp gauge goes all the way up but no warning indicator light comes on the dash. Is this normal operating temp?

 

Not wanting to hijack the man's thread, but while we're on the subject, could this have been avoided by refilling the block before re-installing the thermostat?

thanks
tom

 

Do you have heat? Pull t-stat and fill rad untill coolant is in head at the t-stat local. Reassemble and bring to operationg temp. with heater on. If you have heat , generally, the cavatation is dispursed.

 

The heat is working but the engine temp gauge is going all the way up once the motor is warmed up

 

Everything was fine before this, or was the motor already roasted?

 

The thermostat is not in the heater circuit...coolant flows through heater core all the time. Thermostat only controls radiator flow.

 

everything was fine before this. Maybe the tstat is faulty.