histoy

I drove to Bloomington Gold and experienced unusual temp fluctuations at highway speeds. On the way up I drove the back roads at 55 and the engine ran at 170 to 180 degrees for the first hour, then rose to 210. I switched to the interstate and ran at 65 and the temp remained at 210 for most of the trip. During the last half hour it slowly dropped back to 180 degrees.

On the way home today I drove the interstate at 65 and the car ran between 170 and 180 for the first hour, then rose to 210. I stopped at a rest stop and got out my infrared temp gun to check the temp at the thermostat housing and it read 198 degrees. I checked the temp gauge and it was slightly below the centerline between 180 and 240, so the gauge appears to be working well. We started down the road again and the car ran at 210 (centerline) for the next hour. Then the temp started climbing and it went to halfway between the 210 and 240 points, or approx. 225 degrees. It stayed there for 10 minutes, so I reduced my speed to 60 to see what would happen. The temp stayed at 225 for about 10 minutes then started to fall, and it dropped to 190. I increased my speed to 65 and the temp went back to 210 for the rest of the trip.

Here's some background on the car... I owned it before and it never ran over 180 degrees at highway speeds. It set in a Chevy dealer's showroom for over 11 years and was driven less than 700 miles during that time. Since we bought it back I've changed the antifreeze using a 50/50 mix. I installed a new temp sending unit, because the old one was acting up. The new one reads accurately as checked by the temp gun. I installed a new heavy duty 160 degree thermostat. That's the temp I used in the past. I installed new belts,and tuned the engine. Both the advances are working and I have a total advance of 50 degrees. There is no coolant leaking from the system and there hasn't been any coolant loss. I just read the cooling system article that was referenced in another cooling system post. It said to verify the type of radiator in the car. Mine is an aftermarket radiator with side tanks.

Based on what I'm seeing, I think that the radiator cooling capacity is marginal, and a new radiator may be needed. What are your thoughts?

Gary's '66

It's been my experience that the faster I drive which, is causing the engine to rev higher, the higher my temps will be. I'm running a 3.70 rear end so at 70mph my rpm's are close to 3500 and engine temp will rise to around 210°. If I slow down to 60, rpm's are around 2700 and temp comes down accordingly. NOW, that's just what's normal for my car and that's only on a hot day.
I do know that one thing you should check is to be sure that the spring that's in the lower radiator hose is intact so that the hose isn't able to collapse at high speed (rpm) slowing the cooling systems circulation. And in answer to your last question you're most likely due for a new radiator if it's 11 plus years old.

65GGvert

As I read, I assumed you had a 66 or 67 since you said 210 was the centerline on the gauge. In 64 and 65 the centerline is 180, but your profile says you have a 64. Since you didn't say in the question, I'll assume a 64 with a gauge center of 180.
It does sound like the radiator is borderline to handle the extra heat at the higher engine rpm's. I have a 65 300hp that saw similar upward swings to around 210 at 70 mph (2600 rpm's with a 3:08 rear). When I slowed to 60, the temp would slowly drift back down to 180 to 190. I sprung a leak in the radiator and ordered a new DeWitt's aluminum restoration radiator and put it in a couple weeks ago. I have only driven the car twice, but the temp has not gone above 180 (with a 180 thermo) so far. It would be fairly cheap and easy to troubleshoot by changing your thermostat first, since your temps are going up and down like they would if the thermo closed and opened erratically or stuck. I would try a new one before I paid out for the new radiator. Of course, I would also put in a 180 thermostat, but it's your car and your call.

As an added point, I think what you're seeing is pretty typical for an older car with an older radiator. DeWitt's ad says the aluminum radiator cools 40% better than copper/brass, not sure what you have.

wonderful

I would check for a leaking head gasket. You say no coolant is lost.
Check your thermostat and radiator. I had that happen to my truck and the cause was a leaking head gasket. Added Bar Leak and the problem went away. Will have to change my head gaskets eventually in the future though.

Frankie the Fink

Have the system pressure checked, check your radiator cap and maybe flush the block (I didn't read where that has been done) and then if the problem persists think about the radiator. Easy enough to check for a head gasket leak while you're at it.

There is nothing wrong with a 160* thermostat - its all I run and it only affects the lowest range of operating temp anyway.

Make sure your lower radiator hose isn't spongy and possibly collapsing. I don't know if yours is supposed to have the spring in it but, if so, check for that too.

MikeM

Sometimes your rise and fall in engine temp follows your road speed and sometimes it doesn't. I suspect the thermostat may be part of you problem.

I have a copper radiator in my '65 and the temperature doesn't fluctuate like yours on the highway. My copper radiator is probably 20 years old.

histoy

Thanks for the feedback guys. The temps I recorded were on a cool day... low eighties. The engine runs at 3200 rpm when I do 65 and around 2700 to 2800 range at 60. I forgot to mention that I have the proper shroud and the blades protrude halfway out of the shroud. I just checked and I have a spring in the lower hose, which looks to be in good shape for its age. I also checked the fan clutch and the coil spring is set in the proper notch per the instructions on this site.

BTW... the centerline I mentioned was the mark halfway between 180 & 240 on the gauge. That mark reads 210 with my temp gun.

Vetterodder

My `65 always ran at 180º with a 180 stat then suddenly began running warmer at cruise rpm. Problem turned out to be a failed vacuum canister. Replaced it and all was good again.

histoy

Vetterodder... by vacuum canister do you mean the vacuum advance on the distributor? I replaced mine and the total timing is correct.

VetteJohn

Histoy,

Sounds will something to changingas you drive and the one thing in the collant system that'smade to cange is the thermostat. Just for troublehooting, remove it and see if it acts the same. Better yet, run it up and down the highway and see if it still acts the same. If it does try removing the stat to see if ithe problem goes away. If you you still have the problem at least you're elimiated one thing.

Be careful removing the thermostat when the engine s hot!

Vetterodder

Yes. Sounds like that shouldn't be your problem then.