A weak or defective radiator cap will magnify the condition, the coolant boils later under pressure.
85' cooling trouble
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Heel & Toe
Joined: Apr 2005
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From: Southern Calif
85' cooling trouble
Can anyone verify for me; My 85 runs great and never over heats when running. If I shut the car off when the temp is above 210 or so with fans running the fans stop and coolant will boil out into the overflow. My question is, should the fans continue to run after you turn the ingnition off? They dont. If this is normal, what else would cuase this? Thanks in advance.
Drifting
Joined: Feb 2003
Posts: 1,614
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From: Davis CA
The fans do not continue to run after the car is turned off. However, your coolant should not be boiling out of the reservoir.
The coolant as measured will continue to increase in temp after you turn the engine off but not to an extreme amount. Why don't you check yours by recording the temperature when you turn the car off and then turn the key to on after 5 or 10 minutes and record that temp.
You might have a weak radiator cap or have overfilled the reservoir.
The coolant as measured will continue to increase in temp after you turn the engine off but not to an extreme amount. Why don't you check yours by recording the temperature when you turn the car off and then turn the key to on after 5 or 10 minutes and record that temp.
You might have a weak radiator cap or have overfilled the reservoir.
Team Owner
Joined: May 2002
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
This is perfectly normal. All cars do this. My brand new truck does this.
After shutdown, the engine is still dumping heat into the coolant, but the radiator is not doing any cooling (no flow).
So the coolant heats up, expands past the cap, and as soon as it sees atmospheric pressure, it boils. Yes, it can heat up substantially. I've watched mine go from 230 to 250 after shutdown when running the motor hard.
Remember, the only thing keeping it from boiling at 220 degrees, is the pressure. Once it goes past the cap, it'll boil.
Poster #2 misread your post, poster #3 is wrong.
After shutdown, the engine is still dumping heat into the coolant, but the radiator is not doing any cooling (no flow).
So the coolant heats up, expands past the cap, and as soon as it sees atmospheric pressure, it boils. Yes, it can heat up substantially. I've watched mine go from 230 to 250 after shutdown when running the motor hard.
Remember, the only thing keeping it from boiling at 220 degrees, is the pressure. Once it goes past the cap, it'll boil.
Poster #2 misread your post, poster #3 is wrong.
Team Owner
Joined: May 2002
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
If the cap is weak the system will simply operate at a lower pressure and have a lower boiling point, but unless it's really bad it won't effect the temperature or the amount of expansion that occurs after shutdown. The coolant will still expand out just the same on shutdown and boil just the same in the overflow tank tube.
The only way the cap can worsen this situation is if it's holding so little pressure that the cooling system is actually boiling in the engine or radiator, which will force much much more coolant out than expansion would. This would be a serious problem, and could cause boiling over and overheating while the car was running.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by CentralCoaster
If the cap is weak the system will simply operate at a lower pressure and have a lower boiling point, but unless it's really bad it won't effect the temperature or the amount of expansion that occurs after shutdown. The coolant will still expand out just the same on shutdown and boil just the same in the overflow tank tube.
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Drifting
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From: Mauldin sc
St. Jude Donor '05
Thread Starter
Heel & Toe
Joined: Apr 2005
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From: Southern Calif
Thanks for the replys guys. Heres some more info. The car has 120k miles on it but only about 1000 miles on it in the last 7 yrs due to this problem, mostly sits in the garage. I have replaced the cap twice with the same results. A few years ago I replaced all intake gaskets becuase there were small coolant leaks that I thought was causing the trouble.The boiling is quite a lot when hot, it will fill the overflow and spill out. The radiator and water pump were replaced years ago but have few miles on them.
Race Director
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From: The Top of Utah
Originally Posted by Miket440
The boiling is quite a lot when hot, it will fill the overflow and spill out. The radiator and water pump were replaced years ago but have few miles on them.
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Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Assuming you don't have air pockets, it doesn't take hardly any temperature increase to reach the cap pressure, then the cap begins venting. Pressure builds quickly in a closed system.
Team Owner
Joined: May 2002
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Well crap, why didn't you say so in the first place.
The only time it should ever spill out is if you overfill the tank, and even then it should never spill after it reaches max temp for the first time.You need to burp the system properly and make absolutely sure there isn't a bunch of air in the system. If there is your coolant will boil in the motor and the steam generated will force a bunch of coolant out the overflow tank.
You also need to pull the radiator shroud and make sure there's not a bunch of bags and leaves between the condenser and radiator.