Lately my LS6 has been running very hot. Now the weather is warm, I will admit to that, but it still seems to be running very hot. The car in question is a 1970 LS6 454 with M22, 4.10 Posi, manual steering, cowl induction, all stock motor. I notice on the highway that it runs around 190-200 degrees while driving 60-70 MPH. The coolant is full, and the car has never overheated or belched up coolant. We had a record hot day last week and I took a long ride (55 miles) and the car was wavering between 210 and 218 degrees. No coolant leaks, no known trouble with the water pump. Do you think this points to a problem, or is "this how they are?" Does running at sustained speeds >60 MPH with 4.10s have anything to do with it? BTW the car has polyglass tires also.

Thanks for your help.

Our 4:10 geared L78 does about the same thing in the hot weather. Once the weather cools off it will run at 180 all day.

While these engines have a perpensity to run warm your radiator should be very efficient at highway speeds. Have you read the plugs to make sure that the mixture is not too lean at cruise or the possibility of an intake leak?

Also, do you have a spring in the lower hose? Sometimes the lower hose collapses at higher RPMs only to restrict the flow at cruise.

Just a thought or two ;)

My b-in-law has a 55 wagon with an authentic L78 in it. It runs 200+ in hot/ humid weather, once it cools down below say 85 and the humidity drops it runs under 190 all the time. HTH...john