I have a 1976 cutlass that was just
rebuilt. The engine is running hot on the interstate but good at idle and in town. Please help

 

What pistons were used? What radiator and fan setup?

 

Not sure on pistons. New 2 core radiator with 2 14" electric fans, new upper and lower hoses. New 160 thermostat. Runs 190 in town and at idle jumps to 230 on interstate.

 

Overheating on the highway is usually a clogged (internally or externally) radiator, poor airflow to and through the radiator or an undersized rad. Check the new radiator for cold spots and that the shroud is in place.

Thermostat may not be opening completely. Try another one or test yours.

Does the lower hose have a spring in it to prevent collapse? Ignition timing set with a light and advancing properly?

Did the car run hot before the rebuild? Same block/heads? Two row rad before?

Good luck!

 

Changed thermo from 160 to 190 and back to 160.both top and lower hose have springs. did not run hot before. Original motor and radiator in it before. New heads and 10-1 compression. I am new to all this but I love my car. 76 cutlass supreme with t tops.

 

I have 2 14" fans on back of radiator pulling air towards block.

 

Would a trans cooler help, since torque convertor was changed?

 

OLDSMOBILE LATE 350/403 69 CC ULTIMATE TOP END KIT – Olds Rocket Parts

 

How much overbore? Are you sure the gage is accurate? Carburetion lean? Is all the radiator shrouding in place? Were the correct head gaskets used, there are differences in 350 blocks about that time.

In other words, short of knowing what was done in the rebuild, it could be any one of dozens of things.

 

40 over, using dash gauge
and aftermarket one

 

I tend to think the bottom of the radiator has been compromised (clogged).

Might not hurt to follow this thread...https://classicoldsmobile.com/forums...eating-167084/

 

Your fans may be blocking the airflow. Can also be timing or a lean fuel mix.

 

See if you can detect air being pulled into/through the radiator fins from the front. Are the fans shrouded?

 

Don't use the generic fans. They are worthless. Get a 4000 cfm fan setup on it.. Otherwise if it continues its a shitty cheap aluminum radiator.

 

Ask me how I know?

 

Are the electric fans new to this setup? Could you post a picture of the fans?

 

Champion radiator, 2 14" elec fans.

 

new to this, not sure how to post pic

 

https://classicoldsmobile.com/forums...images-132664/

 

I assume it is the 2 core rad with 1" tubes? Also, are the factory air flaps around both sides and at the bottom of the rad still in place?