To say I have a cooling "issue" is hyperbole at best but I have the same issue that numerous posters have stated. Car runs at 200 all day long on a 95 degree summer day even sitting in traffic w/AC on. However as soon as you get over 3000 rpm (65 mph) for a few miles the temp creeps up to 220/230 and will eventually creep up even more. I know this because for the last 2 yrs I drive her from Mobile to Gulf Shores/Perdido every Monday yr round. It's about 35 miles of Interstate then 20 miles of 55mph Beach Express. By the time I exit the Interstate she's at 220 plus but as soon as I slow down to 55 or 60 (rpm's under 3000) she drops back to 200 and stays solid. Yes I do have propper seals around shroud and other areas.

In the winter months (temps typically 60 to 70 degrees) she runs at 200 to 210 on interstate so I'm skeptical that it's an air flow problem at hwy speeds. I drove 250 miles non stop at 80+ mph to Birmingham last Fall (moderate temps) and she never got over 210. So a couple weeks ago the Clutch Fan started to fail and of course they fail engaged. My 1st clue was how loud the fan is when near fully engaged. You can turn the fan when cool but w/way too much resistance. The last 2 Mondays (temps in the 90's) I did 80mph all the way (rpm at 3400 plus) and she sits right at 200 degrees and never a flinch above. Then when I slowed to 60 mph she drops and holds steady at 190. I'm gonna replace the Clutch Fan eventually but not 'till the Fall. I don't mind the noise at all because at hwy speed it's not that noticeable (I'm a windows down guy) and it's not particularly noticeable skip shifting around town running errands

As mentioned I'm gonna replace the Clutch Fan in the fall because she'll run too cool but I'll keep this one and put her on every summer. I know I could run a hard mount fan in Summer but this one still isn't totally locked in so it's not as loud as a hard mount fan.

Headed down the Beach Hwy

 

The clutch fan running all the time isn't a good reliable way to solve this issue. I would look at your airdam/ splitter being too small or you are missing a key piece of radiator air box seal.

 

At highway speeds, you could remove the clutch fan entirely, and the car will stay cool, if everything else is working correctly.

Have you done the obvious stuff? Pressure test the rad cap. Check for leaks. Make sure the spring is in the lower radiator hose and that it's not collapsing. Etc.

 

Not missing any seals. Even put a bead on space between air dam and body. Again I wouldn't say I have a problem as car never runs hot. But at extended higher rpms on days over 90 degrees she'll creep up but never overheat. Just interesting to note that a more agressive fan keeps her right on the money at hwy speeds on very hot days. When temps are below 90 degrees I can't force her to run over 210 regardless rpm.

I would like a bigger air dam. If someone can show me a link to order a bigger one that fits my 77 I'd order it

 

I don't know if the part is made anymore, or you need to fabricate it yourself. There is a stock air-dam extension for 1979 L82 cars. It is discussed here, with pictures.

https://www.corvetteforum.com/forums...extension.html

 

Yes to all of the above. The car runs perfectly cool at all times yr round and only gets over 200 or 210 at over 3000 rpms on the hwy when it's over 90 degrees outside. I've suspected all along that a bigger air dam would solve the issue. Again if temps are below 90 I can run 80 to 90 mph for 250 miles and she sits right on 200 to 210.

 

Thank you!

 

Hi Mike, out of curiosity, are you sure your temp gauge is accurate?

 

Just throwing this out there. I had a Nissan 300zx and everything worked fine until I got on tthe highway. Eventually I figured out that the old radiator was partially plugged up. At high speed there wasn’t enough flow to cool the engine. Once I replaced the radiator everything work as it was supposed to. Not sure how old you system is but it might be worth considering if all else fails.

 

If the car likes to run Hot then you should check all the vacuum hoses to be sure there are no leaks. A faulty Vacuum Advance can make the engine run a bit hotter. The centrifugal advance could also be sticking which would also keep the engine from advancing while on the highway which leads to higher temperatures.

You might want to check your Knock Sensor for proper operation as when they fail they pull the timing back on all 8 cylinders. IF you have an EGR on your car that could also be a cause as when the EGR fails it makes the engine run hotter combustion temperatures which push the temperatures up.

Anytime there are issues with a cooling system I check the Radiator's pressure cap and verify that the overflow system is connected and working. A bad overflow will allow a air bubble to form inside the radiator and this can push temperatures up as well.

 

I am not and have not worried about it since the car doesn't overheatbut I will get a good temp gun one day.

 

Original radiator has been properly cared for and looks and flows excellent. If it always happened at high speed it'd be a prob but it only happens at sustained rpms over 3000 at above 90 degrees outside. Again she doesn't overheat then either but a stiffer fan action deffinitely keeps the temp right on the money

 

My guess is Clutch Fans up thru the 70's probably funtioned properly and would engage more agressively at over 210 degrees therefore no rampant overheating issues with the hundreds of thousands of Vettes sold. 50 yrs later we're all running whatever junk is out there now and they work up to a point. My failing one is engaed about 80% all the time and as posted makes her run nice and cool at 85 mph in 98 degree Gulf Coast summer heat. So the perfect clutch fan would operate quite and easy yr round and when put under serious pressure durring summertime it'll kick in to 80% on the hwy when needed.

 

Check your lower radiator hose to insure it has a spring in it. At sustained high engine speed, the lower radiator hose can collapse and block coolant circulation. Jerry

 

lucky it fails locked up.
mine failed from having too much slip

 

Bottom hose is correct and functioning beautifully as is the rest of my cooling system. Many have posted that they run perfect except 90 plus degree days at high rpms at high speed. Mine does the same but even then it doesn't overheat, just gets up to 220ish. With stiffer fan action the condition disappears and car runs runs just as cool on a 98 degree day at 85 mph as it does on a 70 degree day.

 

Definitely a bummer. The only other one that's failed on me was 35 yrs ago on my Cutlass and it was 100% engaged and loud as hell. This one still has a little give so it's gonna work fine for the rest of this summer. Gotta find a high quality replacement.

 

A $20- IR temp gun may save you hours of speculation.

 

Looking at the lower radiator hose when the car is in the driveway means nothing. The problem with it occurs at higher speeds ONLY. That lower hose is on the suction side of the pump. When at high speeds, the amount of suction placed on that hose causes it to collapse and essentially block cooling flowing to the pump...IF there is no "anti-collapse" spring placed inside the lower hose. If you can squeeze that hose with your hands and cause it to compress at all (engine off, of course), that is your problem.

 

If collapsed spring in lower hose was an issue on mine (It's not) then temp would creep up under numerous conditions. My car, and many others on this forum, runs perfectctly cool except at outside temps above 90 degrees at hwy speeds above 70 mph. not on an 89 degree day or a muggy 85 but above 90. The car doesn't overheat but it does run 220 plus. I'm telling those w/the same issue that I believe it's a clutch fan issue and a properly funtioning fan will kick in harder at 220 and keep her under 210 at 80mph on a 100 degree day. I know 'cause I did it today. I'm in the market for a true NOS clutch fan.that I believe is more likely to function better than what's out there now.