Running hot @ freeway speeds
Thread Starter
Advanced
Joined: Mar 2014
Posts: 82
Likes: 5
From: Corona Ca
Running hot @ freeway speeds
I had been battling a overheating problem for some time. The temp would stay fine 190 to 200 degrees as long as I was driving around city streets or even sitting in traffic. As soon as I would get on the freeway it would shoot up to 220 and stay right at the point of boiling over until I would slow down. After changing the t-stat,radiator and bleeding the cooling system. I found the answer here on the forum. I just wish I could remember who's post it was so I could thank them personally.It turned out to be the fan clutch. In almost any other vehicle it would get plenty of air at speed but apparently not a 1977 Corvette. After reading the post about the fan clutch I went out in the garage and checked it by starting the engine up cold and holding the rpm's up around 2000 and listening for the fan noise. You should hear the fan moving a lot of air when you first start it. After about 20 seconds it should go away until the engine is hot mine never changed. Put a new fan clutch on drove it to work and back on 7/3 never got over 200 degrees. Now I can focus on repairing the A/C.
Thank you!
Thank you!
Le Mans Master
Joined: Aug 2008
Posts: 5,578
Likes: 61
From: Austin TX
Cool.
I'd just add that I personally avoided buying the HD version of the fan clutch, since all that means is that it comes on sooner and stays on longer, robbing power. I have electric fans on my 71, so no issue for me now.
I'd just add that I personally avoided buying the HD version of the fan clutch, since all that means is that it comes on sooner and stays on longer, robbing power. I have electric fans on my 71, so no issue for me now.
Burning Brakes
Joined: Jul 2009
Posts: 1,240
Likes: 294
From: ESCONDIDO CA
2025 C2 of the Year ('63 and '67) Finalist - Unmodified
C2 of Year Finalist (appearance mods) 2019
I would like a little more explanation about the clutch.
My 69 big pushes the limit for temp when its warm out and the A/C is on. With the motor warmed up and shut off, my clutch lets the fan turn (by hand) with the same minimal effort as when the motor is cold. Is this correct?
My 69 big pushes the limit for temp when its warm out and the A/C is on. With the motor warmed up and shut off, my clutch lets the fan turn (by hand) with the same minimal effort as when the motor is cold. Is this correct?
Thread Starter
Advanced
Joined: Mar 2014
Posts: 82
Likes: 5
From: Corona Ca
Thread Starter
Advanced
Joined: Mar 2014
Posts: 82
Likes: 5
From: Corona Ca
I would like a little more explanation about the clutch.
My 69 big pushes the limit for temp when its warm out and the A/C is on. With the motor warmed up and shut off, my clutch lets the fan turn (by hand) with the same minimal effort as when the motor is cold. Is this correct?
My 69 big pushes the limit for temp when its warm out and the A/C is on. With the motor warmed up and shut off, my clutch lets the fan turn (by hand) with the same minimal effort as when the motor is cold. Is this correct?
Intermediate
Joined: Oct 2013
Posts: 37
Likes: 0
From: Bennington NE
The way I was taught to test a fan clutch is to start the engine cold and hold the rpm's up. You will hear the fan for the first 20 seconds or so then shut off. As you are driving you should hear the fan come on and off also but sometimes it's difficult. I was just very surprised that it did not over heat in traffic. I am considering electric fans also. I wish there was enough room in front of the radiator to add one.
Burning Brakes
Joined: Jul 2009
Posts: 1,240
Likes: 294
From: ESCONDIDO CA
2025 C2 of the Year ('63 and '67) Finalist - Unmodified
C2 of Year Finalist (appearance mods) 2019
I've seen a little improvement in cooling by switching my vacuum advance from ported vacuum to full manifold vacuum. Still a work in progress so the fan clutch is in question. Next time someone warms up a new fan clutch, see if the fan moves at all after shut off.
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