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Ask Your Question1995 Buick Century
Question: Heater/Cooling System Mystery
Question
I've asked a number of knowledgeable mechanics and we're all stumped. Figure this one out and you win the cookie. :)
Symptoms: At normal driving temperature, the temp gauge fluctuates between "Normal" and "Red Zone." When the temp gauge goes UP, the heater blows COLD. Rev up the engine a bit and the temp gauge goes back down to "normal" and the heater blows HOT.
We've replaced: The Radiator, The Thermostat, The Water Pump, We've flushed and back-flushed the block, the Radiator and the heater Core. The Coolant is new 50/50 mix and we've properly bled the air out of the system.
Any Takers?
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Answer #1
Jim Taddei December 30, 2010, 09:11
MasterIt sounds like you may have a blown head gasket or cracked cylinder head. Combustion getting in the cooling system can cause an intermittent air pocket, causing the temperature to rise and the heater to blow cold. If I am right how do I collect my cookie! :)
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Thornysarus, December 30, 2010, 09:22RookieMakes sense, but if that were the case, wouldn't we be seeing oil in the coolant or coolant in the oil? How would we check for this?
I do remember seeing some brownish, liquid-like goo in the PCV Valve when checking for vacuum leaks. Would this also point to a cracked head or blown gasket?
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Jim Taddei, December 30, 2010, 09:41ReplyMasterYou may be seeing the very first signs of a head or head gasket issue. The best test would be to check for CO or HC in the cooling system. You can use a "Block-Check tool or an exhaust gas analyzer held over an open radiator - "sniffing" the hot fumes from the radiator. Please read this RepairPal article - http://repairpal.com/testing-for-head-gasket-failure.
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Answer #2
delane 72 garage and body shop December 30, 2010, 17:15
Masterck vac leak go to inside dash i thank the vac hose u looking for is on driver side heater door is not opening
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Thornysarus, December 30, 2010, 19:03ReplyRookieBut how would a vac leak cause the temp gauge fluctuation?
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Answer #3
Visitor, January 26, 2011, 07:31Replybeginning of head gasket.I had same symptoms.Air in system.So when you rev.it the pump is spinning fast enough to push coolant.Gives you heat.when i was at red light it would blow cold.my temp gauge all over the place.I would bleed system ,add coolant.everything fine.Then coolant level low again more air.I would repeat bleeding process.Eventually the head gasket blew completely.oil in radiator and coolant in oil.Maybe you can just bleed it and add coolant.But if it happens again and no coolant on ground or engine then its going somewhere.
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Answer #4
mastertech6371 September 11, 2011, 12:07Reply
MasterI agree with Jim. you have a head gasket starting to show sugns.
have a shop do a leak down test and a hydrocarbon test to verify.
Roy
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Answer #5
bjm38 February 09, 2012, 17:22Reply
Rookiesame thing for my 2001 saturn sc1 it was a cracked block, since i had just bought the car the dealer just put a new motor in it.
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Answer #6
GOODWRENCH MR April 10, 2012, 13:01Reply
RookieWHAT ABOUT THE HEATER CONTROL VALVE MIGHT BE PARTIALLY OPEN AND NOT FUNCTIONING WHEN YOU REV THE ENGINE IT COULD BE FORCING MORE CIRCULATION THRU THE VALVE AND CAUSING IT TO BE HOT INSTEAD OF COLD AIR ???????????
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