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Topic: 1969 427 Thermostat

in Forum: C3 Engines


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1969 427 Thermostat (1/13)
 11/9/14 5:43pm
rep69
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Suffolk, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 134

I would like to know what is the recommended thermostat to run in my 1969 427 390 hp.  The engine was recently rebuilt. I am not sure what type was installed.  The car is driven in Virginia and currrently the temp is around 200/210 after normal driving.  I have seen either 160/180 degree options.  I am not sure if this will help?  Any suggestions
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Re: 1969 427 Thermostat (2/13)
 11/9/14 6:52pm
LastBigBlock
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Lenexa, KS - USA

Vette(s):
1974 Corvette Convertible 454-4 speed Red / Tan leather / Tan top Frame-on restored driver. SOLD ON DECEMBER 20, 2014 to KCMotorCo.


Joined: 11/9/2014
Posts: 9

My 1974 Corvette with the 454 in it always ran 200-210 when I purchased it during the hot Kansas summer months, so I switched it out to a 160 thermostat with a bottle of "Super Cool" (get at any parts store) added and only a 25% mix of antifreeze (water is a more efficient coolant), and now it runs around 180-190 in the summer and 160-170 in these cooler winter months. Hope this helps!
Re: 1969 427 Thermostat (3/13)
 11/9/14 10:31pm
rep69
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Suffolk, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 134

Thanks..  I will look at getting a 160 . May have to try a couple of different ones to see which works best for my engine. 
Re: 1969 427 Thermostat (4/13)
 11/9/14 10:34pm
Adams' AppleLifetime Member
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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


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Changing to a lower rated thermostat will NOT cause/make the engine to run any cooler, in itself. It only changes WHEN the coolant starts to circulate. A thermostat that opens sooner will get the coolant circulating sooner, which can sometimes help with temp issues. The entire cooling system has to work together to keep engine temps in check. Big block run hot....period. Put one in a small, cramped engine bay as the Corvette has, and the problem just gets worse.
Make sure all the seals are present on the radiator support, around the fan shroud, and across the top of the rad to seal to the hood. Make sure the fan clutch is in working order. Of course, the water pump must also be in good condition. Be sure the lower air dam has the rubber "extension" on it on the '68-'69 models....very important piece that sometimes goes un-noticed.
All that being said, 200-210 is not all that unusual for a big block....but 180-190 would sure be better.

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Re: 1969 427 Thermostat (5/13)
 11/9/14 11:01pm
rep69
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Suffolk, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 134

Thanks. I will look to make sure these were put back on when the engine and radiator were out of the car.   
Re: 1969 427 Thermostat (6/13)
 11/10/14 2:04pm
F4GaryGold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1406

What radiator are you using?

I'd put a 180* thermostat in it.


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Re: 1969 427 Thermostat (7/13)
 11/10/14 5:29pm
rep69
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Suffolk, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 134

I have the original radiator in the car. I had it flushed out, cleaned , and tested with all new hoses and belts installed when the engine was overhauled. 
Re: 1969 427 Thermostat (8/13)
 11/10/14 10:57pm
LastBigBlock
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Lenexa, KS - USA

Vette(s):
1974 Corvette Convertible 454-4 speed Red / Tan leather / Tan top Frame-on restored driver. SOLD ON DECEMBER 20, 2014 to KCMotorCo.


Joined: 11/9/2014
Posts: 9

Those guys brought up good points in that the radiator must be sealed well around the support and the fan clutch and fan shroud must be in good condition.  All of that was fine on my car and I agree that my 160 only difference is that it opens sooner and gives the radiator/engine sort of a head start on cooling.  THE BIGGEST CHANGE was that I always used way too much antifreeze and not enough water so I changed over to only 25% antifreeze and 75% water with an added bottle of "Super Cool Water Wetter" which allows better heat transfer between the water and the metal radiator.....all I know is it worked for me.  My car is always garaged and never left in a freezing situation so the lower concentration of antifreeze doesn't bother me.  The Super Cool also contains a water pump lubricant.  I added an additional front air dam that scoops up air and put in a center grill instead of having a front license plate so there is more air flow coming through.  I still believe switching to higher concentration of water (I use distilled water) and using Super Cool made the biggest difference because standing still at idle, she still stays (relatively) cool.  Hopefully some of this will help your situation also.
Re: 1969 427 Thermostat (9/13)
 11/10/14 11:13pm
rep69
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Suffolk, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 134

Thanks, I checked today and the seals are in place around the radiator. The fan clutch is new. Interesting idea about the mixture ratio.
Re: 1969 427 Thermostat (10/13)
 11/10/14 11:27pm
F4GaryGold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1406

ALWAYS use distilled water.  Especially if you have an aluminum radiator.

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Re: 1969 427 Thermostat (11/13)
 11/14/14 2:00pm
nosal1
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Dunedin, FL - USA

Vette(s):
1980 Corvette Torch Red with Gold metallic 370HP/350 CU.IN.Turbo 350 w/shift kit.Originally CA.Car with 305 CU.IN.


Joined: 3/21/2006
Posts: 262

Hello All and may you all enjoy this day.  I agree with 4 Gary as far as the use of distilled water for any type radiator.I have had experience in evaluating over 50 radiators in Tyler Texas oil field,however I will let that rest and state that distilled water is best. My most important suggestion is a seven blade fan on your fan clutch.My '80 Vette came with a 7 blade fan,albeit a CA. car so anything is possible. My Vette and I spend a lot of time in parades in cruise events,which means a lot of idle time.I have a 185* thermostat and never gets hotter than 195* after idling for very long time.I did last year take radiator out and had it cleaned (this is done every two years) and fresh antifreeze and distilled water.

           I hope this may help in your quest to run cooler temps...Sal C
Re: 1969 427 Thermostat (12/13)
 11/16/14 5:07pm
rep69
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Suffolk, VA - USA

Vette(s):
1969 convertible 427 4speed


Joined: 7/24/2012
Posts: 134

Thanks  I appreciate all the info
Re: 1969 427 Thermostat (13/13)
 11/16/14 6:59pm
F4GaryGold Member
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Grapevine, TX - USA

Vette(s):
1972 LT-1 convertible with factory air.


Joined: 8/26/2006
Posts: 1406

nosal1 said:

Hello All and may you all enjoy this day.  I agree with 4 Gary as far as the use of distilled water for any type radiator.I have had experience in evaluating over 50 radiators in Tyler Texas oil field,however I will let that rest and state that distilled water is best. My most important suggestion is a seven blade fan on your fan clutch.My '80 Vette came with a 7 blade fan,albeit a CA. car so anything is possible. My Vette and I spend a lot of time in parades in cruise events,which means a lot of idle time.I have a 185* thermostat and never gets hotter than 195* after idling for very long time.I did last year take radiator out and had it cleaned (this is done every two years) and fresh antifreeze and distilled water.

           I hope this may help in your quest to run cooler temps...Sal C


Removing the radiator every 2 years is overkill.  Just a flush and refill is fine.


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