C3 running warm on highway

[Steve Sullivan]

No so technical possibility

My 67 experienced similar problems of running hotter at highway speeds but normal at lower speeds. I too checked all the components and finally discovered that the recently added front license plate changed the airflow through the radiator. When I removed it, things were normal. While this might seem unlikely, the big block automatic 67's used an offset front license plate. Worth a try.

[Dave Suesz]

Come to think of it...

the front plate bracket on our C1 was lowered a few inches at the time. Have you tried reducing the timing a few degrees? Our 71 Buick GS would boil over at 12°, ran fine at 10°. Has your engine been bored oversize? This increases transfer of heat to coolant.

[Eric Fairclough]

Re: Is it possible that ...

I would try taking the front license plate off if you have one on. I bought one for my 72 454 then heared that it will run hotter on highway speeds so i left it off. The trans would not make the engine hot. I bought a stock spoiler for mine to push the air into the radiator and it cooled it down more on highway speeds. Mine runs 210 stop and go traffic in 85 degree weather and about 190 highway on the same temperature day. By the way not that this is causing your problem but 160 degree thermostat is too low. You should have 180 degree thermostat instead. The 160 will not give you radiator enough time to cool down. This will make an overall difference. Eric

[Clem Z.]

Re: Is it possible that ...

make sure the bottom hose is not being sucked shut at speed. the BB corvettes had a seal above the rad core support to keep the air from going over the top between the hood and the rad and air will take the path of least resistance which is above the rad. also i had better luck with 5 blade fans vs 7 blade ones on the road. if you are not losing water 220 will not hurt the engine.

[John Walker]

Re: Is it possible that ...

In my wife's 73 the orange warning mark starts at 240 and red at 250.