Running Hot
Thread Starter
Racer
Joined: Jul 2004
Posts: 441
Likes: 1
From: Windsor Ontario
Running Hot
I have a 74 Vette with a 350. It always runs hot, over 200. It runs even hotter with the heat we've been having lately. I changed the thermostat and had the rad cleaned and checked but it still runs the same. The book says it uses a 15 lb rad cap. Will a higher pressure cap make it run cooler or hotter? Should I try a 14 lb or a 16 lb. Or would it matter. Thanx......
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Higher will make it run cooler. Water boils at higher temp under pressure. It won't mae a lot of difference in the operating temp. You might try a good cooling system flush, not the cheap liquid from wallmart, the good stuff from GM
Advanced
Joined: Nov 2003
Posts: 75
Likes: 0
From: saratoga springs ny
I've been dealing with this sort of issue the last several days on a new engine install. A few questions.
Have you verified your gauge accuracy with a heat sensing gun?
Are you getting Run On when you shut the motor off or pinging underload?
How olds your water pump?
DO you notice decent flow in the radiator when the cap is off?
I don't think putting on a higher pressure cap will help your problem. Although I could be wrong water boils at 212F with anti-freeze the boiling temp increases. you might have some areas in your coolant system were coolant flashes to steam and forms a small steam blanket over the cooling surfaces, but something like this would normally cause the temp to creep up and not come back down. Actually a small amount of bubbling increases the heat transfer rate in a forced convection system. But it's a tricky thing to control and normally left to Nuclear Reactor coolant systems.
What's your coolant to water mixture?
Try a mixture with higher water content.
Have you verified your gauge accuracy with a heat sensing gun?
Are you getting Run On when you shut the motor off or pinging underload?
How olds your water pump?
DO you notice decent flow in the radiator when the cap is off?
I don't think putting on a higher pressure cap will help your problem. Although I could be wrong water boils at 212F with anti-freeze the boiling temp increases. you might have some areas in your coolant system were coolant flashes to steam and forms a small steam blanket over the cooling surfaces, but something like this would normally cause the temp to creep up and not come back down. Actually a small amount of bubbling increases the heat transfer rate in a forced convection system. But it's a tricky thing to control and normally left to Nuclear Reactor coolant systems.
What's your coolant to water mixture?
Try a mixture with higher water content.
Last edited by Vermel; Aug 3, 2006 at 10:39 PM.
Burning Brakes
Joined: Jan 2006
Posts: 876
Likes: 1
From: Same as our leaders Out of my mind
I had similar problems and got good results by ditching the stock water pump and installing a Stewart Stage 1 high flow water pump with the recommended Robert Shaw high flow/failsafe thermostat. Under $100 and easy enough to swap out the water pump & t-stat IMO.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by toolman0114
I have a 74 Vette with a 350. It always runs hot, over 200. It runs even hotter with the heat we've been having lately. I changed the thermostat and had the rad cleaned and checked but it still runs the same. The book says it uses a 15 lb rad cap. Will a higher pressure cap make it run cooler or hotter? Should I try a 14 lb or a 16 lb. Or would it matter. Thanx......
I'd suggest a real good coolant system CLEANING ... not just a flush but a real cleanout. Best stuff out there is at GM parts dept ... GM P/N 12346500 it's actually Prestone P/N AS100 Heavy Duty Cooling System Cleaner ... but you'll rarely find it anywhere but dealer ... under $10 ... strong powdered stuff, not those wimpy liquid flushes you'll find at WallyWorld or Advance ... wear eye protection. Get a free DexCool plugged radiator service bulletin (#99-06-02-012D) printout at GM dealer Svc Dept ... it'll walk you through a cleaning procedure that REALLY works. BTW ... proper procedure w/ AS100 takes about 4 hours at high-idle. Use the GM procedure as a guideline ... do it right and this stuff REALLY WORKS WELL!!!!!! Just as tsb instructs: Need NEW t'stat & cap AFTER this thorough cleanout.
And YES ... AS100 safe for aluminum too ... if you use as directed or as in the GM tsb (above tsb is for vehicle w/ alum rad).
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
Just over 200 is not a huge concern. Vettes are not like other cars when it comes to cooling. My buddy's 73 camaro runs cooler than my car and he doesn't have a cooling fan.
Anywho, assuming you have the stock belt driven clutch fan, perhaps your fan clutch is worn out. When the engine is cold spin the fan by hand as hard as you can. It should not turn more than one entire revolution. Also look for signs of oil leaking out of the clutch.
Just a thought.
Anywho, assuming you have the stock belt driven clutch fan, perhaps your fan clutch is worn out. When the engine is cold spin the fan by hand as hard as you can. It should not turn more than one entire revolution. Also look for signs of oil leaking out of the clutch.
Just a thought.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Originally Posted by Nemesis_152
4 hours at high idle sounds like a great way to overheat
and i'm not sure my 75 has the fuel tank capacity for it!
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