Finished up my I swap on my 88 and ran great for a a month or so and then I ran into cooling problems that progressively got worse. It has a brand new head gasket and does not burn oil or coolant at all. For example Ill be driving on the freeway at about 70 and the temperature slowly rises until it reaches 3/4 and which point I have the heat blasting. At this point the heat will go to ambient temperature and then suddenly the temp gauge drops down to a little above a quarter then the heat will come back on like normal. It will repeat this process, I have bled the system multiple times and re tightened all hose clamps and even replaced some. It does not leak coolant when it sits but when I drive it seems to disappear, when I originally did the I swap the coolant was very murky and rusty so I flushed it multiple times. When I was bleeding one morning the themostat was stuck open right when I started the car, this happens occasionally but not alot. Ive considered replacing the radiator and themostat but I am not sure what the issue is. Im stumped and really any advice could be useful.
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If it's overheating while driving it's most likely a flow issue. -
It sounds to me like a defective thermostat. Since that's a very easy $10 fix I would start with that. Next thing would be radiator and after that I may consider the water pump being defective. Even new parts CAN be bad once in a while.Comment
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I've bought a cheapo Wahler thermostat that turned out to be faulty and caused a wandering temperature. Replaced it with a more expensive Behr and that remedied the issue. New thermostat priority numba one!Comment
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Forgot to mention that I did have a new water pump put on when I did the timing belt and have been checking that gasket for leaks but nothing. Just put in a order at pelican parts for a new thermostat, going with Behr this time.Comment
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The cycle of increasing temperature, ending with a sudden drop, and the loss of coolant sounds most like a leaking head gasket that is pumping air into the cooling system. The air causes the engine to run hot and when the pressure gets high enough the cap lifts, venting the air and some coolant.
One DIY check for this is to open the cap when the engine is cold to vent any pressure. At which point the hoses will be soft. Then drive the car just a bit, but not to the point of the temp spike and fall. Then part the car and check to see if the hoses are hard once the car has completely cooled down. If the hoses are hard then, air is being pumped into the cooling system.
Another DIY check is to fully bleed the cooling system, drive the car for a bit, and re-bleed. Release of a significant amount of air on that or a subsequent bleed is evidence of a head gasket leak.
Was the head surfaced (and checked for cracks) when the gasket was replaced?The car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, ALComment
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Get an IR thermometer and verify that your engine is actually overheating. If you are not overheating then I would check the SI board. If you are overheating then my vote is for leaking HG.Comment
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I'm fairly certain that the engine is spiking hot and it isn't because of the thermostat. The combination of symptoms associated with an event:
Occurs at speed
Somewhat eased by the heater
Heater going cold during an event
Sudden drop in indicated temp when the cap lifts
Inexplicable loss of coolant
Are all consistent with an air bubble forming in the cooling system and then venting when the pressure gets too high. Which can only be a head gasket problem or a cracked head.The car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, ALComment
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Originally posted by jlevie View Post
I will check for this right now, head was not surfaced which looking back on was a extremely stupid mistake on my part. The themostat did seem to stick a few time so I am replacing that as they are cheap. Gasket was brand new oem when I did the head swap. Ill come back in a bit to tell you what the diy concluded.Comment
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Another thought that a friend gave me was to get headstuds now as Im going FI soon. This can pull the head down and possibly fix the issue and if not they are reusable versus the stock head bolt application.
What doesn't make sense to me is that I drove the car for about a month and a half, autocrossed and drove it hard. It didnt have a single hiccup. Now it is a issue making the car un driveable. I never overheated the car once either.Comment
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Head studs aren't likely to fix the issue now. The head is going to have to come off, be checked for cracks and surfaced, and a new gasket installed.The car makes it possible, but the driver makes it happen.
Jim Levie, Huntsville, ALComment
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I ordered headstuds and Im going to put them in and see if a difference is made. If not its just going to be easier to take on and off the head from now on.Comment
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Put the head studs in, It may have actually fixed the problem. Before it could have been Idling and it would spike as described before. Now I have no such issues, will drive the car tomorrow and see what it does.Comment
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my problem is similar, so won't make new topic, but post here.
I have the same problem, after driving, especially after engine run some while in high rpms (some drifting/high speed speeding - long time high rpms etc), hoses gets veery hard.
I have this engine (m20b25) for 3 years now, problem is from the very beginning.
so main radiator has been changed, water pumps 2 times, expansion tank cap, engine rebuilt 3 times, head checked for cracks, maany thermostats gone :D etc
sometimes had the same problem as topic author, system was bleeded etc, but driving long distances, sometimes temp started to rise, then suddenly drops to ok and stays here.
all times when head gaskets were changed, block surface was just cleaned with paper knife and then polished with fine sandpaper etc, no machining.
also no greases added on head gasket.
any suggestions? really engine block? (does really those cast iron blocks crack so often?).Comment
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