Overheat on a cold day

Tiny
JIMFLAN1
  • MEMBER
  • JEEP CHEROKEE
I have a 1994 Jeep Cherokee 4.0L with 170k miles. Temp was -18 this morning. Warmed up 8 mins (love remote start). Defrost was on, but when I got in to leave house, no warm output yet. My initial thought was that it was just really cold. After driving short way, switched to regular heat to see if heat would pump out. Within 30 seconds of this, noticed steam from under hood. 10 seconds later temp light came on. I immediately pulled off and shut vehicle down. Really hot coolant was escaping fast from radiator cap. I let her cool down and got her back to the house, less than a mile - temp light did not come back on and no bad noises, so I'm praying no engine damage. Replaced thermostat few months ago along with fresh coolant, so a little perplexed. I'm thinking thermostat, cap, or maybe coolant mixtue ratio. Any advice?
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Tuesday, January 16th, 2007 AT 2:17 PM

6 Replies

Tiny
CEARL
  • MEMBER
Any pin holes in any of the hoses? Could you smell coolant in the cabin before the steam appeared (from the heater core)? If not I'm looking at the waterpump with a prayer in mind. Definately check the issues you're thinking but I would add a couple of other things to look at since I'm there. Check out the water pump. First look for the weep hole, you probably know but, its a small hole cast in the waterpump housing. If you have coolant coming out there the seal in it is history. If your looking good there grab the pully and give it shake. If you have more than nominal play here you may have lost a bearing or bushing in the pump. Don't forget to let the tension off the belt for this check. Lastly, and worst yet, refill the antifreeze and start the engine. If the coolant begins to boil very quickly, a matter of minutes, you may have a cracked head. But that is not my first bet. There is comfort in knowing that if in the unlikely event that the head is cracked these are among the easier ones to R&R and they are readily available. Good luck.
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Friday, January 19th, 2007 AT 12:30 AM
Tiny
RASMATAZ
  • MEMBER
Are you sure you have the proper mix in your coolant to protect you down to -18degs maybe it freezed on you-No coolant flow.

A 1mo. Old Stat can give you the worst nightmare-so recheck it. I've been there before trust me.

HTH-Good Luck!
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Friday, January 19th, 2007 AT 6:34 AM
Tiny
JIMFLAN1
  • MEMBER
Thanks for the response. Please don't forget about me. I'll be checking the possibles that you both gave. No coolant on dipstick (not milky). Coolant should have been able to handle the temp, but then I didn't exactly measure 50/50 or 70/30. Steam and coolant was coming from radiator cap and nowhere else as far as I could tell. Going to look some more this evening so please check back. Just haven't had the time to confront my nightmare - so it's just been sitting.
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Monday, January 22nd, 2007 AT 5:00 PM
Tiny
JIMFLAN1
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No sign of warped head. Mine is cast iron. That's comforting. Changed oil and no sign of coolant in there. Nice and black. Drained coolant. Came out fairly clean with very little scale and no sign of an obstruction in the radiator. Not much came out (maybe 2 quarts), so I'm thinking there wasn't enough and that was the initial problem. Installed new water pump and thermostat. Filled radiator with fresh coolant/water. Started engine and all sounds and looks good. Ran it with radiator cap off for about four minutes. Turned on heat and within 30 seconds again got the overheat light. Shut down. Heater hose still cold, lower radiator hose cold, upper radiator hose warm from thermostat to about halfway to radiator. Engine does not seem overly hot. A slight wisp of steam coming up through open radiator fill tube. Thinking no flow through thermostat, probably due to air in system, and it never did burp. Confirmed no flow past thermostat as there was no coolant when I pulled heater hose and upper radiator hose. Decided to pull the thermostat and drill a little hole in it to let the air pass through, allowing coolant to reach the thermostat. But need a new gasket first. Will try that. If it works to bleed the air out of the system, I will install a new thermostat thereafter. Otherwise, I am completely stumped. Don't think the heater core is cloggled, because that would most likely be gradual. Also, the heater hose would still be warm and the rest of the system would theoretically work properly - just no heat. Any other ideas, or am I on the right track with the air thing?
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Friday, February 2nd, 2007 AT 10:42 AM
Tiny
RASMATAZ
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Replace the thermostat and bleed it.
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Friday, February 2nd, 2007 AT 3:37 PM
Tiny
JIMFLAN1
  • MEMBER
To double check for blockage, poured coolant through heater hoses. Core checked out fine with good flow. Filled engine block and up to cylinder head through heater hose connected to the water pump. No blockage. Re-Installed thermostat with little hole at 12 o'clock and then added a little more coolant via heater hose. Reconnected heater hose and checked all connections. Started up with radiator cap off. After several minutes, got a nice burp (blub blub blub) and coolant level dropped good. Topped off coolant in radiator and capped it. Let run for several more minutes and after shut down good vacuum from reservoir. Problem solved and she's running like new again. My lesson. Check that coolant strength and level every year before it gets cold. Fixing this problem in the cold weather is no fun at all. Thanks for the help guys.
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Tuesday, February 6th, 2007 AT 11:31 AM

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