Overheats on Freeway
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
Overheats on Freeway
My engine runs up to 220 deg at highway speeds. Around town, the temperature stays right at 190. I've tried standard and high flow water pumps and there is no difference in temperature readings. Also had the radiator rebuilt. With the cap off you can see that it flows perfectly well. I have all the radiator seals/shrouds installed and a large spoiler/airdam. My plugs seem to look fine. I don't think I'm running too lean on the carburetor. What could cause this problem?
A blocked water passage in the block? When I had the engine rebuild machine work done I had problems with the machinist doing things right. He made significant errors on the balance and had to do it all over again. Perhaps that is not the only thing he messed up
I also have very high oil pressure. Could this be related? I have a high volume oil pump which I bench calibrated (cut the spring) to 55 psi. When the engine is cold pressure is 70 psi. I'm using 15-50 synthetic.
The car is a 68, 427 390hp w/ 10:5 forged pistons, L88 closed chamber heads, L71 mech cam, Holley 750 vac, RG 5-speed 3.08 rear.
Before the rebuild it never ran hot except in traffic in hot weather...normal for a big block.
Thanks in advance.
A blocked water passage in the block? When I had the engine rebuild machine work done I had problems with the machinist doing things right. He made significant errors on the balance and had to do it all over again. Perhaps that is not the only thing he messed up
I also have very high oil pressure. Could this be related? I have a high volume oil pump which I bench calibrated (cut the spring) to 55 psi. When the engine is cold pressure is 70 psi. I'm using 15-50 synthetic.
The car is a 68, 427 390hp w/ 10:5 forged pistons, L88 closed chamber heads, L71 mech cam, Holley 750 vac, RG 5-speed 3.08 rear.
Before the rebuild it never ran hot except in traffic in hot weather...normal for a big block.
Thanks in advance.
Racer
Joined: May 2001
Posts: 401
Likes: 0
From: Carlsbad CA
Sounds like you've already ruled this out, but every car I've ever had that overheated (Corvette, '68 DeVille, '79 Blazer, '95 4Runner), the culprit was a bad radiator. Someone else may have more suggestions, but having chased the problem on too many other cars, that would be my guess. I know that sealing the fan shroud completely may contribute to the problem on Corvettes, so you may want to look at the foam seals between the shroud and the radiator while you're waiting for other replies.
Good luck!
Good luck!
Instructor
Joined: Jul 2003
Posts: 107
Likes: 0
From: New Berlin WI
same condition only a small block
Bronzebb:
I have the same condition. Motor just rebuilt, and in car. Supposedly a 180 thremostat was installed, but at freeway speed I approach 220 as well. Like your car oil pressure seams high at 75 lb.
My situation though is a 350 w/9.5:1 C.R. backed up by a Tremec. I also have a high volume pump, and radiator before rebuild operated normally and temp never exceeded 180
I have the same condition. Motor just rebuilt, and in car. Supposedly a 180 thremostat was installed, but at freeway speed I approach 220 as well. Like your car oil pressure seams high at 75 lb.
My situation though is a 350 w/9.5:1 C.R. backed up by a Tremec. I also have a high volume pump, and radiator before rebuild operated normally and temp never exceeded 180
Last edited by 1979L82; Jul 15, 2005 at 10:13 PM.
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Overheating
The point or alluded point of too high an oil pressure is interesting. I have a bb454 with a high volumn Melling oil pump running the same pressures. At idle it runs about 190 and on the highway 200-210. I think this is just normal for a bbc as there is one heck of a lot of iron in there to cool. If someone has comments on oil pressure vs operating temps - please speak up. Thanks.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 207
Likes: 13
From: Belmont California
It just seems wrong for it to overheat at speed. The faster I go, the hotter it gets. It never had this problem before the rebuild. The only different engine component after the rebuild was switching from 10.25:1 cast pistons to 10.5:1 forged. Anything above 75 deg air temperature and it will overheat.
I'd pull the engine out again if I had to and was sure what the problem was.
I'd pull the engine out again if I had to and was sure what the problem was.
Le Mans Master
Joined: Jul 2005
Posts: 5,752
Likes: 4
From: Austin Texas
Borrow a Infrared thermometer (or buy one). Gauges and temp sending units can be 10-20 degrees off! Aim at the radiator tanks and thermostat housing. I'll bet the temp. is lower than the gauge shows...lol
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Melting Slicks
Joined: May 2002
Posts: 2,716
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
Mine would do the same thing, fine in town and would heat up on the interstate. I repaired the seals around the radiator and core support to force all the air through the radiator and added the chin spoiler to force air into the void in front of the radiator. This fixed my problem. The temp sensor should be mounted in the head if it is than the temps at the radiator will be cooler than the gauge indicates.
Neal
Neal
Racer
Joined: Apr 2005
Posts: 339
Likes: 1
From: San Diego CA
There have been a lot of temperature threads lately, mine included. My car does that too.
A week or two ago someone suggested that the air might be "stacking up" in front of the radiator, possibly due to a bad fan that acts like a barrier at high speed, or the air not being able to get out of the engine compartment fast enough.
What really bothers me about my vette's cooling system is when I compare it to my newer SUV. Newer cars never overheat (for the most part), and the temperature is incredibly consistent even on a 100 degree day idling with the a/c going. What is so different about my new car and my old vette...besides electric fans???
A week or two ago someone suggested that the air might be "stacking up" in front of the radiator, possibly due to a bad fan that acts like a barrier at high speed, or the air not being able to get out of the engine compartment fast enough.
What really bothers me about my vette's cooling system is when I compare it to my newer SUV. Newer cars never overheat (for the most part), and the temperature is incredibly consistent even on a 100 degree day idling with the a/c going. What is so different about my new car and my old vette...besides electric fans???
Drifting
Joined: Feb 2001
Posts: 1,603
Likes: 0
From: San Francisco, CA
Originally Posted by 71SoCal
What really bothers me about my vette's cooling system is when I compare it to my newer SUV. Newer cars never overheat (for the most part), and the temperature is incredibly consistent even on a 100 degree day idling with the a/c going. What is so different about my new car and my old vette...besides electric fans???
Race Director
Joined: Nov 1999
Posts: 10,643
Likes: 8
From: Foxfield CO 1970 Convertible
I don't think 220 is too hot at all. The temp gauge goes all the way to 250 (at least on mine) so that's pretty much normal. Mine ran that way right from the factory all the way to 315,000 miles. Also, I doubt if your SUV has a 427 with a 26in. radiator on a slant a few inches above the pavement... 
If you're worried about a temperature fluctuation, maybe at highway speeds your engine is leaning out? This might add to higher temperatures...
If you're worried about a temperature fluctuation, maybe at highway speeds your engine is leaning out? This might add to higher temperatures...
Race Director
Joined: Jul 2002
Posts: 11,593
Likes: 173
From: Clayton NC
Originally Posted by lvjohn
Sounds like you need to check the clutch fan, i have one on my 71 big block runs 190-195 in summer(las vegas summers) 
I hate just adding that but as said above by photovette and lvjohn it's the fan clutch that is shot. If you get the car up to temp and put a piece of tape on a fan blade. Then turn off the motor and watch how many times the fan rotates. It should only rotate about 4 times or so before stopping. If it keeps spinning you fan clutch is toast... Dave..
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
Le Mans Master
Joined: Oct 2002
Posts: 5,714
Likes: 6
From: Silver City NM
St. Jude Donor '05-'07
Originally Posted by 71SoCal
What really bothers me about my vette's cooling system is when I compare it to my newer SUV. Newer cars never overheat (for the most part), and the temperature is incredibly consistent even on a 100 degree day idling with the a/c going. What is so different about my new car and my old vette...besides electric fans???
I agree, there have been a lot of posts lately about Vettes "running hot". I think many guys are comparing operating temps of an OLD car that normally ran hot with newer cars that normally run cool by design. Two different animals. If it goes over 220, then you can start to worry.
Over 230 shut off the engine and let it cool down. Do NOT run it at 250!!!!
Oh yeah....when you shut it off and then get in and fire it up a few minutes later you WILL see the temp gauge jump way up. This is normal. It should drop back down after about 30 seconds. If you are living in a place like Phoenix, Arizona, and the temps outside are 114, expect your engine to run hotter than normal. Just make sure you have some decent 20W-50 oil in it and keep an eye on the temp gauge.
Also, running the A/C WILL raise engine temps.
Dep
Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Fan Clutch
Originally Posted by PhotoVette1
Mine did the same thing until I installed a Carquest HD thermal fan clutch. 195F tops now with a/c on in 95F sunshine at 75mph... worth $46.
Instructor
Joined: Jul 2004
Posts: 139
Likes: 1
From: Folsom CA
Originally Posted by lvjohn
Sounds like you need to check the clutch fan, i have one on my 71 big block runs 190-195 in summer(las vegas summers)
Try putting on a cheap flex fan and see what that does to the temperature ranges. U can always take it back to Kragen :-)
Le Mans Master
Joined: Oct 2002
Posts: 5,714
Likes: 6
From: Silver City NM
St. Jude Donor '05-'07
Originally Posted by turtlevette
Wuus,
obviously you have never done any REAL racing.
obviously you have never done any REAL racing.
Dep