Overheating on Freeway
Thread Starter
Intermediate
Joined: May 2014
Posts: 48
Likes: 1
Overheating on Freeway
Most of my driving is in city traffic, stop & go almost never over 50 MPH. It have never goes much over 210 degrees no matter what the outside temperature is. It is 106 here today and most likely will remain over 100 through September. Today after 2 miles on the freeway @ 75 mph the temperature was pushing 250 with the a/c on. I turned the a/c off but did not notice a significant decrease in engine temperature. After a 15 minute cool down, I drove in city traffic for several hours with the a/c on and did not experience any issues. The car is a stock 81 with no mods. The timing is set correctly, the anti freeze is a fresh mix of Prestone 50/50, new radiator cap and new 180 degree thermostat. All of the weatherstrip in the engine compartment is in place and I have the stock fan shroud installed. My first question is, would it be a solution to replace the fan clutch with the correct length spacer? Is it possible that the bottom hose is collapsing at higher speeds? Is there a way to check for that senario? Any suggestions will be appreciated.
Last edited by charleyahrens; Jun 2, 2014 at 06:08 PM. Reason: grammar
Thread Starter
Intermediate
Joined: May 2014
Posts: 48
Likes: 1
Most of my driving is in city traffic, stop & go and almost never over 50 MPH. It has never gone much over 210 degrees no matter what the outside temperature is. It is 106 here today and most likely will remain over 100 through September. Today after 2 miles on the freeway @ 75 mph the temperature was pushing 250 with the a/c on. I turned the a/c off but did not notice a significant decrease in engine temperature. After a 15 minute cool down, I drove in city traffic for several hours with the a/c on and did not experience any issues. The car is a stock 81 with no mods. The timing is set correctly, the anti freeze is a fresh mix of Prestone 50/50, new radiator cap and new 180 degree thermostat. All of the weatherstrip in the engine compartment is in place and I have the stock fan shroud installed. My first question is, would it be a solution to replace the fan clutch with the correct length spacer? Is it possible that the bottom hose is collapsing at higher speeds? Is there a way to check for that senario? Any suggestions will be appreciated.
Le Mans Master
Joined: Oct 2006
Posts: 6,842
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From: Palmdale CA
It's pretty easy to check the radiator hoses. When the car is cold, go on and give the upper and lower hoses a good squeeze with your hand. They should be shiny and firm. If they feel like an grandma's arm and are soft, spongy and grey looking, then it's time to replace them.
Drifting
Joined: Apr 2005
Posts: 1,917
Likes: 451
From: Central NJ
2-air pocket?
First I would get the nose up by driving up on a set of ramps then run her and fill radiator. If that doesnt work then check the thermostat.
2026 Loser of the Year
Joined: Sep 2013
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From: New Or-leens Loo-z-anna
Double check the fan clutch while the car is idling to make sure the fan is turning fast.....BE CAREFUL IF YOU TRY TO TEST THE FAN CLUTCH......a folded piece of long cardboard slowly pressed against the fan blades should NOT STOP the blades from turning fast...if it does, the fan clutch is going bad
Burning Brakes
Joined: Oct 2001
Posts: 911
Likes: 5
From: TN
timing a 1981
Was your timing set with the distributor vacuum advance canister disconnected and the vacuum line plugged?
Is your vacuum advance operational?
Are you using full time vacuum advance, straight from the carb to the vacuum advance and using a full time vacuum source at the carb?
Is your vacuum advance operational?
Are you using full time vacuum advance, straight from the carb to the vacuum advance and using a full time vacuum source at the carb?
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It's timing. You are most likely at a part throttle cruise on the highway. So there is still vacuum advancing the timing. Retarded timing will over heat the engine quickly, too much advance will do it very slowly usually assisted by detonation. Can you hear any pinging? Try retarding the timing a few degrees and see if you still over heat on the highway.
Good Luck!
Good Luck!
Thread Starter
Intermediate
Joined: May 2014
Posts: 48
Likes: 1
Thread Starter
Intermediate
Joined: May 2014
Posts: 48
Likes: 1
Was your timing set with the distributor vacuum advance canister disconnected and the vacuum line plugged?
Is your vacuum advance operational?
Are you using full time vacuum advance, straight from the carb to the vacuum advance and using a full time vacuum source at the carb?
Is your vacuum advance operational?
Are you using full time vacuum advance, straight from the carb to the vacuum advance and using a full time vacuum source at the carb?
Thread Starter
Intermediate
Joined: May 2014
Posts: 48
Likes: 1
Also turn on the heater and make sure it is blowing hot air while you have it on the ramps.....sometimes it takes 20 minutes to "burp" all the air out of the coolant passages.
Double check the fan clutch while the car is idling to make sure the fan is turning fast.....BE CAREFUL IF YOU TRY TO TEST THE FAN CLUTCH......a folded piece of long cardboard slowly pressed against the fan blades should NOT STOP the blades from turning fast...if it does, the fan clutch is going bad
Double check the fan clutch while the car is idling to make sure the fan is turning fast.....BE CAREFUL IF YOU TRY TO TEST THE FAN CLUTCH......a folded piece of long cardboard slowly pressed against the fan blades should NOT STOP the blades from turning fast...if it does, the fan clutch is going bad
Thread Starter
Intermediate
Joined: May 2014
Posts: 48
Likes: 1
It's timing. You are most likely at a part throttle cruise on the highway. So there is still vacuum advancing the timing. Retarded timing will over heat the engine quickly, too much advance will do it very slowly usually assisted by detonation. Can you hear any pinging? Try retarding the timing a few degrees and see if you still over heat on the highway.
Good Luck!
Good Luck!
Thread Starter
Intermediate
Joined: May 2014
Posts: 48
Likes: 1
It's pretty easy to check the radiator hoses. When the car is cold, go on and give the upper and lower hoses a good squeeze with your hand. They should be shiny and firm. If they feel like an grandma's arm and are soft, spongy and grey looking, then it's time to replace them.
Drifting
Joined: Jul 2011
Posts: 1,697
Likes: 139
From: Syracuse NY
Is all the foam in place around the radiator? I know this is the most often quoted reason, but its also the most overlooked. My inserts were missing around the perimeter. I used to hit 220 on highways and it wouldnt cool down until it sat for a few hours. I replaced the foam with generic Home Depot insulation and I now sit at 190, she hits 205 in traffic, 195 highway.
Drifting
Joined: Jun 2012
Posts: 1,990
Likes: 183
From: Port St. Lucie Fl
Is all the foam in place around the radiator? I know this is the most often quoted reason, but its also the most overlooked. My inserts were missing around the perimeter. I used to hit 220 on highways and it wouldnt cool down until it sat for a few hours. I replaced the foam with generic Home Depot insulation and I now sit at 190, she hits 205 in traffic, 195 highway.
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
Generally speaking, at freeway speeds you should have sufficient airflow across radiator (I believe you said the stock pieces were there). Suspect radiator efficiency. Is your radiator old? Also, make sure your pump is up to snuff. I like Flow Kooler pumps...
Good luck.
Good luck.
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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A better test for the clutch fan is to start you car cold, let it run for two minutes and shut the car off and check the resistance to turn the fan.
Restart the car and run for ten minutes (up to normal operating temperature), shut it off and you should have MORE resistance to turn the fan.
Don't use a spacer, if your clutch is bad get a new one.
Restart the car and run for ten minutes (up to normal operating temperature), shut it off and you should have MORE resistance to turn the fan.
Don't use a spacer, if your clutch is bad get a new one.