getting hot on highway
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getting hot on highway
I replaced the heater hoses, heater core, thermostat (failsafe 185*), and radiator hoses in my 78 460 C6 4x4 and now the stock temp gauge goes almost to the H and it never did this before. It used to warm up quickly and stay about in the N or O in normal but now it stays cool in city driving and seems to get hot on the highway after about 30 min driving about 65 mph. As soon as I got off the highway it cooled back down. I have seen that most people don't go by the factory gauge but it seemed fine before I changed everything. Any ideas? I believe it's the original radiator, fan shroud, but an aluminum flex fan that was on there before.
Postmaster
Joined: Nov 2011
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On the highway ram air is helping so the fan doesn't matter much. Usually hot moving means the radiator is getting plugged. Less likely, the vanes have rusted off the WP or the lower rad hose is getting sucked shut (does it have a spring inside?) My only question is did this just start with the new Tstat? If so the T stat may be defective or the wrong type. Some engines, like my 400, really need the correct stat to cool correctly. Its worth checking/changing the stat and checking/adding the lower radiator spring before tackling the radiator.
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I never thought about the lower radiator spring but the old hose had one and the new one doesn't. That makes sense so I'll get a new one. Thanks blue and white. I think I'll try a different thermostat too. The guy at napa said the computer showed a 185* for my truck. I didn't think the radiator was bad because this problem wasn't there before and I changed just the antifreeze two years ago so it was just turning brown from yellow, it's yellow again now.
Posting Guru
Joined: Oct 2007
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From: Sedro-Woolley, WA
I never thought about the lower radiator spring but the old hose had one and the new one doesn't. That makes sense so I'll get a new one. Thanks blue and white. I think I'll try a different thermostat too. The guy at napa said the computer showed a 185* for my truck. I didn't think the radiator was bad because this problem wasn't there before and I changed just the antifreeze two years ago so it was just turning brown from yellow, it's yellow again now.
Fleet Owner
Joined: Dec 2009
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From: NorCal
yah, the lower radiator hose is supposed to have an anti-collapse spring to address the water pump's negative pressure at high RPM.
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Senior User
Joined: Feb 2013
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From: Nor-cal
Don't failsafe t-stats open once and then fail in that position? Almost like having no t-stat at all? Maybe that's causing overheating going down the highway. I don't claim to be an expert, but that's what I would look into first. Good luck.
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Post Fiend
Joined: Mar 2011
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From: Lynchburg, VA
A stuck open thermostat causes excessive warmup time, not overheating.
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