Highway overheating diagnosis?
Melting Slicks
Joined: Apr 2000
Posts: 3,286
Likes: 8
From: San Jose California
Re: Highway overheating diagnosis? (RickP)
I have 3 Spal Fans with over 3000cfm of air flow. Pretty impressive, huh! Guess what, that means the air is only flowing at 25mph through the radiator. YOU DON'T NEED A FAN AT HIGHWAY SPEEDS!!!
Duntov knew this and solved the highway speed cooling problem by retrofitting into the early production C3's a spring loaded door (waste gate) to allow the air that backs up behind a spinning fan to spill out. A fan at highway cruise is turning much too slowly to allow the air to pass. A spinning blade blocks air, it doesn't help the flow. Kind of like using a horse to pull start your car, once it's going, the horse is only in the way.
Try taking the fan out. It's pretty easy to remove. I drove my dual quad 350 setup in my Vette for over a year with no fan whatsoever. This was when I lived in a rural area with virtually no stop lights and absolutely no traffic jams. No problems and never, never over heated!
Please excuse me for sounding like a flame, but it really amazes me at how strongly so many wonderful Corvette folks continue to believe a fan does any good at 70mph.
Chuck
Duntov knew this and solved the highway speed cooling problem by retrofitting into the early production C3's a spring loaded door (waste gate) to allow the air that backs up behind a spinning fan to spill out. A fan at highway cruise is turning much too slowly to allow the air to pass. A spinning blade blocks air, it doesn't help the flow. Kind of like using a horse to pull start your car, once it's going, the horse is only in the way.
Try taking the fan out. It's pretty easy to remove. I drove my dual quad 350 setup in my Vette for over a year with no fan whatsoever. This was when I lived in a rural area with virtually no stop lights and absolutely no traffic jams. No problems and never, never over heated!
Please excuse me for sounding like a flame, but it really amazes me at how strongly so many wonderful Corvette folks continue to believe a fan does any good at 70mph.
Chuck
Melting Slicks
Joined: Apr 2000
Posts: 3,286
Likes: 8
From: San Jose California
Re: Highway overheating diagnosis? (Chuck Harmon)
I need to add that I recently recalibrated my temp gage. When I installed the engine I had to use a new sender and was warned by the parts guy that the replacement senders read hot. Mine was checked against a thermometer and was indeed 40 degrees hot. Meaning that the gauge read 240 when the coolant was actually only 200. Never assume!
I corrected the problem by installing a 15 ohm resistor into the wire that attaches to the sender. It now only reads about 5 degrees hotter than actual.
Chuck
I corrected the problem by installing a 15 ohm resistor into the wire that attaches to the sender. It now only reads about 5 degrees hotter than actual.
Chuck
Thread Starter
Heel & Toe
Joined: Aug 2001
Posts: 21
Likes: 0
From: Marlborough MA
Re: Highway overheating diagnosis? (Daves_rusty_75)
Can you describe how that looks? The top of my shroud is curved, and the air filter duct sits on top of it. It looks like the photo for new shrouds int he catalog. The bottom of the shroud looks like maybe it was cut or trimmed...
Thread Starter
Heel & Toe
Joined: Aug 2001
Posts: 21
Likes: 0
From: Marlborough MA
Re: Highway overheating diagnosis? (bigvette1)
Thanks for the advice. The air/fuel mix, HEI advance, timing and gear ratio all check out fine. So I'm ready to pop another thermostat in there with some drilled holes. Or should I leave it out and test drive it?
My '77 is auto with AC.
Does the viscocity of the oil make a difference on engine heat? I put in some pretty thick oil last summer--I forget - w50?
My '77 is auto with AC.
Does the viscocity of the oil make a difference on engine heat? I put in some pretty thick oil last summer--I forget - w50?
Thread Starter
Heel & Toe
Joined: Aug 2001
Posts: 21
Likes: 0
From: Marlborough MA
Re: Highway overheating diagnosis? (Rockn-Roll)
I got the air/fuel mix and timing checked. They're perfect. I added a heavy viscosity oil last summer. Does that increase friction and heat? Should I go back to 10W40?
Pro
Joined: May 2001
Posts: 596
Likes: 0
From: Yardley PA
Re: Highway overheating diagnosis? (Chuck Harmon)
The gauge could still be your problem then. I remember calculating the curves once and even with a parallel resistor the curve with the new sender unit was much too steep. Don't remember the actual numbers, but it could be that at reading 260 she's only running 220-230. Still too hot for comfort, but maybe a clue.....
Stefan
Stefan
