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Re: OEM temp gauge readings [message #357767 is a reply to message #357738] Sun, 16 August 2020 21:46 Go to previous messageGo to previous message
Rick Staples is currently offline  Rick Staples   United States
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
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Senior Member
Chris wrote:
"... I noticed the gauge has gone as high as just between the quarter and half mark while on the highway, and I never hear the fan roar like the old one. But, when getting off the highway or slowing to 55 MPH or so, the needle settles back to the quarter mark."

This appears to be a case of a bad (clogged/scaled) radiator. The fact it cools off at lower speed to me rules out the fan as a problem, as you normally need the fan more at LOW speed than on the highway. Of course the execrable aerodynamics of our GMC engine compartment and grill make the fan necessary at all speeds. Of course the engine needs more cooling under load. If the radiator is clogged up or internally coated with scale or rust, it can't transfer enough heat to the passing air. In an extreme case the air might not even be warmed enough in passage at speed to get the cooling fan thermostat to engage. I suspect this may be your situation.

Many years a go I had a Citroen which I loved dearly, and a beautiful young lady I wished to impress. She wanted to go to the beach one hot summer's day, so off we went. It was over 90F, and any time I went over ~50mph, my temp gauge would climb, so we drove down and back with the heat on to prevent boiling over. Needless to say, she was not impressed. Next day, I pulled the radiator and took it to a shop to be cleaned ("rodded out"). Problem fixed, but too late for that "one that got away". Wink

Unless some other cause presents itself, (double-check the thermostat) I'd recommend removing the radiator and taking it to a radiator shop (if you can find one these days) for disassembly and cleaning. Or you could replace it. You may be able to see down into the tanks with a borescope or something to examine the core passages.

My 2ยข,, HTH
Rick Staples

Rick Staples, '75 Eleganza, Johnstown, CO "Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien

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