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The 68 heated up to 240* at stop light.. Help

jims427400

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Jun 7, 2005
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763
Location
Temperance Michigan
Corvette
67 427 tripower,68 427 tripower,04 Z16, 62 340hp
Drove the 68 home for the first time tonight. It was a little shaky, vibrations through 1st and 2nd gears. 3rd gear pops out during down shifting but my initial concern is that at a long red light the temp guage climbed quickly to 240*. Its got a new water pump and thermostat 180*. One thought I have is the fan clutch spins freely w/ very little resistance. Can this cause the car to heat up quickly. If not , any other thoughts.. Oh yea, it was like 85* outside
 

jims427400

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Temperance Michigan
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67 427 tripower,68 427 tripower,04 Z16, 62 340hp
One last comment, as soon as I got rolling again, the temp came down..
 

fine69

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Dec 12, 2004
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975
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Maryland / D.C.
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'69 Convertible Vette; '72 Z28 Camaro Rally Sport
Drove the 68 home for the first time tonight. It was a little shaky, vibrations through 1st and 2nd gears. 3rd gear pops out during down shifting but my initial concern is that at a long red light the temp guage climbed quickly to 240*. Its got a new water pump and thermostat 180*. One thought I have is the fan clutch spins freely w/ very little resistance. Can this cause the car to heat up quickly. If not , any other thoughts.. Oh yea, it was like 85* outside

Yes, the fan clutch can be a contributor to the heat problem.

When you stop your engine the fan should continue a few times. If it continues to spin, you should replace the fan clutch.

Good luck to you. I know a hot car can be misery.
 

petes74ttop

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Oct 22, 2006
Messages
392
Location
Mount Holly N.C.
Corvette
1974 T-Top
When you shut off the motor the fan should stop in 1 or 2 seconds, if it spins longer than that it's time to get a new fan clutch. PG
 

jims427400

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Jun 7, 2005
Messages
763
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Temperance Michigan
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67 427 tripower,68 427 tripower,04 Z16, 62 340hp
Thanks 69,
I may be spoiled but I cant imagin how these original owners drove these cars on hot summer days. I was roasting and that was even w/ the top down.
A new fan clutch is in my future.
 

68Roadster

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Dec 16, 2002
Messages
1,040
Location
Dallas, TX
Corvette
'68 White Vert '05 Silverado SS
Jim,
Hope the clutch fixes the temp problem....
I can sympathize with ya on the top down roasting problem....by the time I get home my back is wet with sweat.....need to replace my top and get the A/C working again......always something!
 

bossvette

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May 19, 2003
Messages
3,233
Location
West Unity Ohio
Corvette
1968 1997
do you have a shroud around the fan?
 

Wayne robson

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Feb 24, 2007
Messages
169
Location
australia
Corvette
sold my last corvette.
cooling

Hello.the best test for fan clutch on a corvette is at cold motor condition, approx 70 degrees,pull your fan as hard and fast as you can by hand, and it should not spin more than half to three quarters of a turn, on other gm cars Buick Caddy Olds, etc, its still ok with approx one to, one and a half spins, also there should not be any significant play in the side or bearing movement.
1 other reasons,low coolant.
2 faulty radiator pressure cap
3 thermosstate stuck shut
4 slipping belt
5 timing
6 corroded system.

regards wayne.
 

SIXFOOTER

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Jul 15, 2007
Messages
117
Location
Boca Raton Fl
Corvette
1981 L81 Tan Coupe
a Note on the fan clutch, it shoule make less that 1 turn when you shut the motor off while it is warm
It sounds to me like you had air in the system, like mentioned above it will act like low coolant, once the thermostat opened up it may have equalized. Fill it with 50/50 and take a ride see what happens, take the 50/50 with you
The way to avoid trapped air is to drill a couple of 1/8" holes in the thermostat before installing it. That allows the air to bleed off filling the water jacket with coolant
 

chevy6673

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Sep 23, 2006
Messages
286
Location
illinois,crete
Corvette
1973 Corvette ,1966 ss impala
When you shut off the motor the fan should stop in 1 or 2 seconds, if it spins longer than that it's time to get a new fan clutch. PG
ok lets recap i have a 73 L 82 in my 66 the fan cluch not sure what it came from swap meet part, i turn off the motor it stops not even 1 turn,, but then i can turn by hand freely is it good or bad ;shrug
 

jims427400

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Messages
763
Location
Temperance Michigan
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67 427 tripower,68 427 tripower,04 Z16, 62 340hp
I have the same result.. turn motor off and maybe 1 rotation. Turn motor off and spin by hand-very little resistance, but my machanic says its bad. hmmm
 

chevy6673

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Sep 23, 2006
Messages
286
Location
illinois,crete
Corvette
1973 Corvette ,1966 ss impala
I have the same result.. turn motor off and maybe 1 rotation. Turn motor off and spin by hand-very little resistance, but my machanic says its bad. hmmm
WELL MAYBE MINE IS ALSO BAD LET ME NO WHAT YOU END UP DOING AND IF YOU GET A NEW ONE HOW DOES IT ACT WHEN MOTOR IS OFF;shrug;shrug
 

petes74ttop

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Joined
Oct 22, 2006
Messages
392
Location
Mount Holly N.C.
Corvette
1974 T-Top
ok lets recap i have a 73 L 82 in my 66 the fan cluch not sure what it came from swap meet part, i turn off the motor it stops not even 1 turn,, but then i can turn by hand freely is it good or bad ;shrug

I have the same result.. turn motor off and maybe 1 rotation. Turn motor off and spin by hand-very little resistance, but my machanic says its bad. hmmm

I just tried mine, the cars been parked for 6 hours, I cannot get 1/2 turn by hand, so I agree it's BAD. Try http://www.lbfun.com/corvette/tech/vettetech.html lots of info there. Scroll down to cooling.pdf by John Hinckley. Hope this helps, PG
 

minifridge1138

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Joined
Feb 2, 2007
Messages
908
Location
USA
Corvette
1982 Black Fastback
I have had a LOT of experience with my corvette overheating.
Here is what I did, and the order I did it in:
1) check fluid. Check the reservoir and check in the radiator itself. Make sure there IS fluid in it.
2) make sure the fan spins correctly. You've already got plenty of info on that.
3) Check the thermostat. Many thermostats stay closed when they fail and fluid can not flow. Replace with a 180 degree Mr. Gasket (when they fail, they stay open).
4) Check radiator. If it was leaking and someone put a can of stop leak in it, then odds are good that it is clogged. Buy a new radiator or have the brass/copper one re-cored. Personally, i bought a Direct Fit Aluminum radiator from DeWitt's. Nobody makes a better radiator.
5) Test water pump. I don't know the best way to do that (my problem was the radiator).

(can you tell that overheating is a common problem in C3's ?)
 

6880 Mike

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Jun 30, 2006
Messages
2,723
Location
The Bluegrass State
Corvette
1968 convertible; 1980 L-82
Add these to the list:

Correct radiator in good condition.
All required radiator support seals.
Correct fan shroud.
All required fan shroud seals.

:)
 

Koop

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Mar 16, 2005
Messages
545
Location
Kalifornia
Corvette
YELLOW 69 modified GM Crate ZZ383, LS2 TBSS
Why don't ya'll just pull out that thermostat?

Bubba. :gap
 

mason1968

Member
Joined
Nov 9, 2005
Messages
21
Location
Santa Cruz, CA.
Corvette
1968 corvette roadster
I have a 1968 with a GM350 create motor with a B&M 144 supercharger. I had the same overheating problem as jims427400 reported.

My solution required me to replace the water pump, radiator and the pulleys, listed below is what I did.

New water pump from Stewart stage 3 water pump and the recommended thermostat rated at 165 degrees. http://www.stewartcomponents.com/

Radiator from dewitt, this is a direct fit aluminum radiator. http://www.dewitts.com/

New overdrive pulleys from March Performance. http://www.marchperf.com/ The overdrive pulley will spin the water pump faster. This is a requirement for the Stewart Stage 3 water pump the increase speed increase the water pump pressure at idle.

I also use a flex-a-lite 7 blade unequally spaced blades. This increased the air flow thru the radiator at idle.

After all of the changes the engine never, and I mean never, have the water temperature go past 180 degrees and most of the time it will stay at 165 degrees which is the rating of the thermostat.
 

mason1968

Member
Joined
Nov 9, 2005
Messages
21
Location
Santa Cruz, CA.
Corvette
1968 corvette roadster
Oj I forgot to mention that you should replace all of the seals that are between the radiator and the radiator supports.

It is very important to have the area ahead of the radiator sealed completely to ensure that the are flowing into the front passes thru the radaitor.
 

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