Topic: Over Heating
in Forum: C3 Cooling and Heating Systems
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Ok I have replaced the radiator the thermostat and the hoses. The car seems to run about 200 to 220 in city traffic. But it runs to 240 to 260 on the highway. Should it be the other way around if I have a heating problem? What would cause this?
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Lifetime MemberMundelein, IL - USA
Joined: 6/9/2008
Posts: 411
Vette(s): 1978 25 anniversary blue on blue with T-tops.
Might be water pump. Did you check weephole and see if its leaking. do you have an electric fan or original? I replaced water pump last year and that did the trick for a while but now radiator is gettin put in.
Lifetime Member #150
Recent Modifications 
"Drive it like you stole it"
No the water pump is not leaking. I have the fan clutch it has to be that sense it gets hotter at higher speeds? I could just replace the water punp for JP its not that hard.
Lifetime MemberMundelein, IL - USA
Joined: 6/9/2008
Posts: 411
Vette(s): 1978 25 anniversary blue on blue with T-tops.
not hard but can be a PITA removing the fan clutch. Auto parts do not always carry the studs either for the fan clutch. I had to reuse some of the old ones and they were no fun getting them off.
Lifetime Member #150
Recent Modifications
"Drive it like you stole it"
Lifetime MemberModerator
Moses Lake, WA - USA
Joined: 4/16/2005
Posts: 2134
Vette(s): 1976 L48 4-spd, Mahogany Metalic exterior, Buckskin interior 350ci/350hp, 3rd owner, fiberglass spring, 255/50-16's Torq-Thrust II
Had the same problem with mine when I first got it. I live in the desert region so it was not surprising to have a cooling challenge. If I went above 70mph on the hwy the vette would over heat. If it cools in city traffic your fan and clutch are probably ok. Do you have the foam seals between the radiator and radiator mount (both sides, bottom and top). This will prevent the air from by pass the radiator. Also the seal between the top of the radiator mount and hood. Have you checked you engine timing? If your off a ways the engine will run hotter. Is you chin spoiler in place. It helps to deflect air up and into the radiator
My problem was I had a 3 row radiator core with the A/C. Went to the 4 row and it solved the problem but still ran a bit hot on hot days. When I put the new motor in I went with Diwitt Aluminum radiator and dual electric fans. It now stays nice and cool!
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Frederick, MD - USA
Joined: 9/8/2003
Posts: 3398
Vette(s): 1969 convertible L71 427/435 4-speed black interior
Check out your lower radiator hose. It should have a spring inside it to prevent collapsing under vacuum. What you're experiencing is classic symptoms of a collapsing lower hose...fine at low speed but as speed and rpm's rise, the hose collapses under vacuum, thus preventing coolant flow. The spring will prevent that. You could have a hose missing a spring.
Other possibilities...make sure all seals are in place around the radiator as already said, the shroud is in place, the air deflector under the front end is in place, you have a good radiator cap that holds pressure properly, the radiator and block cooling passages are clear of sludge, etc.
From your description, it sounds like the lower hose has no spring or the air deflector/seals aren't there or are improperly installed.
Lifetime MemberApache Junction, AZ - USA
Joined: 10/15/2006
Posts: 285
Vette(s): 1982,150K,Renegade CFI,Hooker Side Pipes,85 fuel pump,Bilsteins,HD suspension, Aluminum radiator, SharkBar/w 5-Point Restraints. 3:73 gears coming soon.
I agree on the seals, a lot of air flow is lost without them in place - all of them in place, also the hose collapsing.
I also fought overheating for a good three years and installed a high flow pump, aluminum radiator, dual fans, new hoses and Water Wetter; STILL had problems until I connected the the dual fans up properly. Now my fans are receiving the correct amps and blowing the rated CFM - FINALLY no more over heating. 180 to 210 even at 112 degrees in the shade with the AC on!
I also fought overheating for a good three years and installed a high flow pump, aluminum radiator, dual fans, new hoses and Water Wetter; STILL had problems until I connected the the dual fans up properly. Now my fans are receiving the correct amps and blowing the rated CFM - FINALLY no more over heating. 180 to 210 even at 112 degrees in the shade with the AC on!
check the belts they might be loose, belts don't always squeal when loose, when you have to push volumns of water at highway speed a loose belt may not be turning the waterpump fast enough.
mines was running a high temperature at one time until I replaced the heads. Mechanic was going to put in valve seals because it was smoking at startup and running idle, discovered i had a bad head, bought a reworked pair, lowered the temperature . Now runs from 180 to 200 max on a 100 degree day.
Do you have the air dam spoiler under the front lower grille panel. If it is missing it will not divert the air up into the radiator at hwy speed. Mine was missing and I had the same problem at hyw speed. I also keep the antifreeze to -10 only and use water weeter in the radiator and we stay nice an cool.
in Forum: C3 Cooling and Heating Systems
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