bronzebb

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.

thebruce

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!

DJ Dep

Ummmm....220 is NOT "overheating" for your engine.

Dep

1979L82

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

bigvette1

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.

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.

bronzebb

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.

big_G

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

chevymans 77

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

71SoCal

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???

R. Bruno

Look at where the Vette radiator is compared to the SUV. The SUV radiator has air ramming right through at highway speed, while the Vette depends on those three vent holes underneath to bring air up and through the radiator.

Z-man

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...

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)

Hitch

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..

rihwoods

http://www.haydenauto.com/fce2.htm

DJ Dep

Most new cars make EXTENSIVE use of aluminum. Aliminum heads, water pumps, blocks, etc. Much easier to cool and keep cool.

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

bigvette1

What is the difference between this and the stock GM or a Hayden or an Autozone with the thermal strips? Thanks

73LS4

Can't remember how many times I been down this road. If it doesn't overheat in town, sitting at a stoplight with the a/c on... which is where it should get the hottest... then I'm bettin on the fan clutch. The clutch uses a different mechanism that senses heat when you're out on the highway. It uses a centrifugal force mechanism when you're sitting at the stoplight.

Try putting on a cheap flex fan and see what that does to the temperature ranges. U can always take it back to Kragen :-)

turtlevette

Wuus,

obviously you have never done any REAL racing.

DJ Dep

I don't need to tape up the grille like you do to get good times. I only race for a matter of SECONDS.

Dep