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Themostat stuck closed?

B

BrokenXJ

NAXJA Forum User
Location
Massachusetts
My son overheated the XJ last night. I figured the aux/fan did not come on, so I told him the fill up the radiator with water and blast heat for the 2 mile return home.

He gets home and says the heat was not that hot, and the temp got up to 250-260! on the way home.

I checked the radiator and it only needed a cup or two of water? The car was still about 150 degrees so fired up the engine with the cap off, figuring I would add more antifreeze as it circulated. Then gushers of antifreeze come out of the radiator, as the engine is running and warming up. Temp quickly gets up to 240, aux fan is on, and I shut it off.

Is this a symptom of a stuck thermostat?
 
You should pull the thermostat and test it in a pan on the stove with a thermometer.

You didn't mention the year/engine.
 
BrokenXJ said:
2000 XJ, Just boiled the themostat and it opened right up :dunno:
Click to expand...

Really sounds like a cracked head/headgasket.

You probably have a 0331 head, infamous for their failure rate.

Do a search for "0331 head".
 
Wait, more info. Just replaced the thermostat because I needed to re-install it anyways. Drove it 6-7 blocks and the temp was 220. Turned on the heat, no heat. Pulled over into a parking lot at 250, and get this. The upper radiator hose was rockhard, overflow bottle was full, but heater hoses, lower radiator hose, and radiator cap were basically cold ?

Could the radiator be plugged? which way does the water flow? and I would think if the upper hose is hot, that the heater hoses would be also?
 
From water pump through thermostat and upper hose to radiator, down through radiator, back through engine.

Radiator could be plugged, so could the heater core. May have caused a blown head/gasket, might (very slight but possible, are you feeling lucky?) be the only problem.
 
BrokenXJ said:
Could the radiator be plugged? which way does the water flow? and I would think if the upper hose is hot, that the heater hoses would be also?
Click to expand...

A blown head gasket may be adding excess pressure to the cooling system...but...

Coolant flow is from radiator thru lower hose to water pump, block, and t-stat, heater core. T-stat gets hot enough, opens, allows coolant into upper hose to be recirculated and cooled. Coolant should be circulating thru heater core at all times (hot or cold) on a 2K since there is no heater control valve.

The heater core could be plugged, especially if your heat is dim. So, if your heater hoses are not as full and/or hot (approximately) as your upper hose I'd be looking at the core. Try flushing it independently of the rest of the system.

After it all cools down and the pressure is off, CAREFULLY remove the heater hoses from the firewall. Flush from top to bottom, bottom to top, back and forth until all you get is clear water. You don't need or want the hose on real high pressure (don't use a nozzle, gun, etc.). Just regular pressure from the hose should dislodge most crap.
 
exact same symptoms as an explorer i had.(no heat,hard hoses,spewing water out of the cap) hate to tell ya but its head/headgasket time.clogged rad and or heater core would be gradual not all at once
 
Flushed the heater core. It didn't seem that bad. Turn the petcock on the radiator and nothing is coming out. Plastic petcock turned vertical to spout, nothing? Started it up, and it came up to temp extremely fast. This doesn't' make sense like mentioned above, that the radiator could clog this fast. I am replacing the radiator for $150 no shipping a radiator.com I think this partially my fault, I used block sealer to fix the heater core last year.
 
BrokenXJ said:
Flushed the heater core. It didn't seem that bad. Turn the petcock on the radiator and nothing is coming out. Plastic petcock turned vertical to spout, nothing? Started it up, and it came up to temp extremely fast. This doesn't' make sense like mentioned above, that the radiator could clog this fast. I am replacing the radiator for $150 no shipping a radiator.com I think this partially my fault, I used block sealer to fix the heater core last year.
Click to expand...

yah, that is one detail that would have helped out greatly to know earlier. be sure to thuroughly flush the entire cooling system before installing the new radiator or you could damage the new one as well.
 
stewie said:
yah, that is one detail that would have helped out greatly to know earlier. be sure to thuroughly flush the entire cooling system before installing the new radiator or you could damage the new one as well.
Click to expand...

Stewie, would one of the commercial flushes, like Prestone, be could at cleaning the block sealer?
 
stewie said:
yah, that is one detail that would have helped out greatly to know earlier. be sure to thuroughly flush the entire cooling system before installing the new radiator or you could damage the new one as well.
Click to expand...

Replace the water pump while your there as well. That crap will destroy the pump bearings as well. It's also possible the water pump impeller is mangled up and not pumping.
 
joe_peters said:
Stewie, would one of the commercial flushes, like Prestone, be could at cleaning the block sealer?
Click to expand...

i dont know if it will remove all of it, but you would for sure want to get any loose particles or excess of it out of there before installing a new radiator. when i took apart my old leaking radiator (to seperate the types of metal and to see just what the trans "cooler" was inside the rad) i noticed a lot of semi-metalic bits of debris in there. i never use that stop leak crap as i know it can clog stuff up. i made sure to flush my cooling system quite regularly now to make sure none of the crap the prior owner put in there is gonna clog my new rad
 
I block sealed my '90 and it works well - no heater core issues.

I'm suspicious of the "no heat at the core, but overheating." That is a prime symption of a huge air bubble - ie, low coolant from an underfilled system. The heater core gets empty and as the coolant circulates, slowly fills it to the detriment of the block, which gets less and less until it overheats.

When any Cherokee needs lots of coolant added it's a good idea to get the filler neck elevated so that air will move out of the system. It's not so easy on a Renix, fortunately the others just need to point uphill.

Not getting enough coolant will cause overheating and a cold heater core on every car I've owned.
 
Methinks you're wasting money on a new radiator. If you pull the lower radiator hose off, does it all drain out quickly? Those drain petcocks are mostly wasted anyway. As stated before, it's likely combustion exhaust in the cooling system. Have you done a compression test on the cylinders?
 
X2 on a compression test - before you buy anything, get a tester and you will have concrete information, not guessing.
 
OK, I've eliminated the radiator and the air bubble. I fugured the radiator needed replacing because it won't drain. I purchased a 99 cent flush kit that I attached to the heater hose to top off the system.

Called AAA to tow it to my mechanic, he said he has somekind of fluid test that turns color immediately if exhaust gases enter the system. He also said very rarely, something with the waterpump impeller could be broken.

I still think it's strange that there is no heat? I'll let you know the final out come.
 
Unless the thermostat is specifically designed otherwise (cf: Stant's "FailSafe" line,) the first overheat of a thermostat will wreck it and freeze it shut. That's why they're replaced out of hand if you overheat the thing.

So yeah, your thermostat is wrecked. Find out why you overheated in the first place, fix that, and change the thing.
 
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