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Topic: Hot at high RPM

in Forum: C3 Cooling and Heating Systems

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Hot at high RPM (22/32)
1/29/07 11:50am

bytor
Former Member
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Simpsonville, SC - USA

Vette(s):
1978 25th. Silver Anniversary Edition 350 L-82 Stock

Joined: 1/21/2007
Posts: 85

Yes, both the lower and upper hoses have springs installed. I still do not understand why the "upper" radiator collapses at high RPM. After the car warms up, I could rev the engine and watch it suck shut before I installed the spring. What's the likelihood that I have a reverse direction water pump installed. I contacted the previous owner and he had replaced the water pump within the last year because it leaked. He never had any overheating problems before that. Humm.... I not sure how I could check to see if it's pumping the correct direction or not.

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Hot at high RPM (23/32)
1/30/07 1:09am

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 20129

Unless you're spinning the pump backwards, it ain't like to be the problem.
When you rev the engine up like that, it creates a vacuum in the water passages. It's caused by the pump pumping the water in quicker than letting it out. The thermostat is essentially a restriction in the system. The water going out has to go thru the thermostat, and that slows it down, but the pump is still trying to pump. So...it "sucks" on the intake side of the pump. Once there is a vacuum, something has to give, and rubber hoses being what they are, that is the give.
If the cap has the correct rating, and the overflow is not restricted, this bit of suction shouldn't really be an issue. The cap should allow the vacuum to pull coolant back out of the overflow as needed.

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Hot at high RPM (24/32)
1/30/07 10:41pm

bytor
Former Member
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Simpsonville, SC - USA

Vette(s):
1978 25th. Silver Anniversary Edition 350 L-82 Stock

Joined: 1/21/2007
Posts: 85

Ok, pump is not running backwards, duh. I went ahead and replaced the thermostat. This time I �burped� the system afterwards. With the radiator cap off started the car and waited for the tstat to open. Upper hose began to get warm and a minute later coolant burped out the radiator cap and the coolant level dropped out of sight then came back up. I could see the tubes in the radiator and they had water flowing through them fine. My question is, how may time do I let it burp? Once or continue till it stops?

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Hot at high RPM (25/32)
1/30/07 10:48pm

Norsky

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Burke, VT - USA

Vette(s):
SOLD - "The Toy" - '70 Convertible
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Joined: 1/23/2002
Posts: 7191

Once eveything has warmed up be sure to open the heater to full blast to get some coolant flowing through the heater core. There could have been an air bubble hiding in there.

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Hot at high RPM (26/32)
1/30/07 11:05pm

Adams' Apple

Burp it till she pukes! Oh wait...that's fer babies...never mind.

A couple of times should be fine. Then put the cap on, make sure the overflow is FULL, and then drive it a while. As the engine cycles thru the temp range, it will pull the coolant it(the radiator) needs from the overflow tank. Once it no longer empties the overflow, it should be full to spec. Then, just see that the overflow tank is at the correct level for "Hot". Drain or fill as needed to get it to the "hot" level, and you're done.

If all is well, once it cools back down to cold, the level in the overflow will be up to the "Cold" mark.

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Hot at high RPM (27/32)
1/31/07 12:34pm

Relbiker
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Peoria, AZ - USA

Vette(s):
1981 two tone beige/bronze,believed to be one of 200 4 speed cars from bowling green,all original with 29,000.miles

Joined: 2/16/2006
Posts: 4

it's the hose

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Hot at high RPM (28/32)
2/1/07 10:53am

bytor
Former Member
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Simpsonville, SC - USA

Vette(s):
1978 25th. Silver Anniversary Edition 350 L-82 Stock

Joined: 1/21/2007
Posts: 85

This looks like a neat effective way to purge the air out of you cooling system. http://www.allhead.com.au/cooling.html

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Hot at high RPM (29/32)
2/1/07 1:36pm

dwright
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Victor, NY - USA

Vette(s):
2004 Commemorative Edition Coupe, Auto w/HUD. 13K miles in 2015. Sold 1982 Red Coupe

Joined: 7/12/2004
Posts: 6836

GOOD INFO. I PRINTED IT FOR FUTURE USE.

THANKS.

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Hot at high RPM (30/32)
2/3/07 1:12pm

bytor
Former Member
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Simpsonville, SC - USA

Vette(s):
1978 25th. Silver Anniversary Edition 350 L-82 Stock

Joined: 1/21/2007
Posts: 85

Bypassed the heater core and used the method above to get the air out. Presto, no more overheating..

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Hot at high RPM (31/32)
2/3/07 1:48pm

gs77vet
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Joined: 3/19/2005
Posts: 385

The best thing to do is replace the radiator, water pump and hoses and maybe a heater core and the resourvoir and hoses .This is expensive but you should be done with overheating. I replaced all these things except the heater core.
The overheating was a downer, everytime I went on a trip I had a heating problem. Gene

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Hot at high RPM (32/32)
2/3/07 2:34pm

eddie20875

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Lanoka Harbor, NJ - USA

Vette(s):
1975 metallic blue coupe with t-tops,L48, t/t steering, black leather interior. 1990 L98, white/red leather interior, auto,a/c

Joined: 12/21/2006
Posts: 828

only problem with that gs besides being expensive is that you really don't know what the problem was and what you did to correct it. as in bytor's case it seems to have been air trapped in the system which could have still happenned if he replaced everything.

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