Recently bought 71 Cutlass Supreme. Temp runs up to 220 on highway,drops to 200 in town driving.New waterpump,radiator flushed by a dealer using Petra flush system.New 180 thermostat.Fan seems to be operating properly.350 with a/c. Looks like original radiator. I’m not a mechanic but I may have to start training.Lots of issues with this Olds. Thanks for any help.

 

Have you gone over your tuneup settings? Is the radiator clogged, even though you did a flush? Is there anything blocking the radiator to limit air flow?

 

Be sure that the radiator is clean inside & outside. You can look for cooler spots with a temperature gun. Check the ignition timing. Try to get things back to original specs and see what it does. Check the thermostat to be sure it is opening properly.

 

What RPMs are you turning on the highway and have you checked the lower radiator hose to be sure it isn’t collapsing? Should have a spring in it to prevent that.

 

Going to have timing checked again,spring in lower hose,radiator looked by good shop nearby,maybe heat up new stat before putting it in. Thanks for response.

 

These temperatures are perfectly normal. I had a '75 Chevy Nova that ran at 210 all day long for the 10 years I owned it. Who told you the engine is overheating? It is not.

 

No, its not normal for the hwy cruise temp to be a lot higher than in town slow driving temp.

 

Yes, high RPM at cruise speeds can definitely lead to elevated temperatures.

My car will run at 180º all day around town but at 70+ MPH with the AC on in 100+ summer temps the engine is turning 3400 RPM or so and the coolant climbs above 210º. If I slow down to below 3000 RPM the coolant temp drops below 200º. Just not enough radiator cooling capacity to dissipate the heat generated by the engine at those RPM, ambient temps, and AC operation.

 

Thanks for all the info.

 

Just curious.....The previous owner didn't remove the shroud, did he?

 

You could try a 180 high flow thermostat, probably will not help. It sounds like a flow issue vs air flow. As said, usually cars run hotter at low speed. The fan basically is not needed at speed and the shroud also should not be needed at speed. Make sure all the air dams are in place and maybe drain out the coolant then add a couple of things of CLR or similar, drive around for a week then flush good.

 

FYI
The original purpose of the spring in the lower hose is for the vehicle manufacturer to be able to fill the cooling system on the assembly line using a vacuum method. Period. It is true the spring will keep the hose from collapsing. However if the hose is getting sucked closed it is because of a restricted radiator that cannot supply enough coolant to the suction side of the water pump.

 

High highway temperatures vs cooler in town temperatures may be caused by a transmission defect causing the transmission to run hot.