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The aftermarket temperature gauge has helped diagnose the problem. The factory gauge is not accurate at all under 200, but after 200 it seems to be more reasonable. I guess that's where you'd want the accuracy anyway...
With A/C on at 94*, driving slightly uphill on way home, 65mph, I was able to get it to 235* before I shut the A/C off and yielded to the desert sun. I was able to get it back down to 205* in about 2 minutes. Turn A/C back on, temp starts climbing.
I'm kind of at a loss. I've sealed the top of the hood area, and done everything I can think of to force air to have to go through the condenser/radiator at speed. And I also have the dual SPAL's cranking the hole time.
After driving I can touch the condenser, it isn't that hot... The radiator is obviously a lot warmer than the condenser.
I'd think if it was a transmission issue (tranny cooler lines are in the radiator), or a timing issue, I'd overheat with or without the A/C on.
Another update, I know there are a lot of these threads and every one kind of has different solutions and ways to tackle it, so I figure it's good to have it all documented here for others with the same issue.
I built my own air dam extender from pvc strip from the hardware store. Instead of the 2" the stock dam provided, it's now 5", with still plenty of ground clearance.
I drove for about 30 minutes, 80* outside (it is dark though...) and I never got the motor over 190*, even going up the big hill I take from work at 75mph for 15 minutes, with the A/C running. And for the first time ever while driving down the road, the electric fans kicked off! (I turned off the A/C at the end of my ride and drove around the neighborhood to see how low it would go. Gauge was reading 175*, right where the fans kick off, I've never seen it that low while driving.
So I think the issue, big surprise I'm sure to a lot of you with experience, is the car is hard to get air to... It also looks like having the headlights up let's more air in, so it's something I might try if I start getting hot (flip the lights up).
While doing the project, which took all of about $10 and an hour of my time I might add , I discovered that my overflow tank for the coolant is right behind the license plate, basically blocking a lot of air that would flow up to the air dam and get kicked into the radiator. I can't find anywhere better to put it right now, but that might need a relocation to help even more.
I'll try and drive it in the heat tomorrow and see what happens
In your very first post, you indicated that the air/fuel ratio was verified. Exactly how was this done? At idle on a smog machine tester? Do you have an Air/Fuel ratio gauge installed in the car, so you can monitor it at all times? Because if it's running either too rich or too lean, it can have a major effect on the heat output of the engine. It may even be a clogged fuel filter causing the lean condition, by dropping the amount of fuel when the demand is high. The thread below is pretty extensive, but worth a read.
"Now that the advance curves are correct, it is time to check the jetting or air/fuel mixture. It is also very important to be sure that the fuel pump can supply enough fuel volume and pressure, even at high loads. The fuel pressure we use most is 5 ½ to 6 lbs. at all speeds, and this pressure must be maintained even at high loads. If the fuel pressure drops at high loads, the fuel mixture will go lean and create a heating problem. An engine that is jetted too lean will create more heat than an engine that has the correct air/fuel ratio; if the jetting is too rich, the mixture may still be burning in the headers and exhaust system, again creating more heat. Many of the overheating problems that we have seen are due to a lean-at-part-throttle problem that is very common on many original equipment and aftermarket carburetors; this lean-at-part-throttle condition can create an overheating problem at light throttle. The newer, reformulated, gasoline that can shift the air/fuel mixture leaner by about 2.7% has brought many of these lean mixture problems on. If the air/fuel mixture is too lean at any driving condition, the engine will create even more heat for the cooling system to dissipate."
In your very first post, you indicated that the air/fuel ratio was verified. Exactly how was this done? At idle on a smog machine tester? Do you have an Air/Fuel ratio gauge installed in the car, so you can monitor it at all times? Because if it's running either too rich or too lean, it can have a major effect on the heat output of the engine. It may even be a clogged fuel filter causing the lean condition, by dropping the amount of fuel when the demand is high. The thread below is pretty extensive, but worth a read.
"Now that the advance curves are correct, it is time to check the jetting or air/fuel mixture. It is also very important to be sure that the fuel pump can supply enough fuel volume and pressure, even at high loads. The fuel pressure we use most is 5 ½ to 6 lbs. at all speeds, and this pressure must be maintained even at high loads. If the fuel pressure drops at high loads, the fuel mixture will go lean and create a heating problem. An engine that is jetted too lean will create more heat than an engine that has the correct air/fuel ratio; if the jetting is too rich, the mixture may still be burning in the headers and exhaust system, again creating more heat. Many of the overheating problems that we have seen are due to a lean-at-part-throttle problem that is very common on many original equipment and aftermarket carburetors; this lean-at-part-throttle condition can create an overheating problem at light throttle. The newer, reformulated, gasoline that can shift the air/fuel mixture leaner by about 2.7% has brought many of these lean mixture problems on. If the air/fuel mixture is too lean at any driving condition, the engine will create even more heat for the cooling system to dissipate."
The shop hooked up some vacuum hoses and some sort of sensor on the exhaust I believe. If my most recent air dam extension doesn't solve it my next step will be to have an independent shop test the air/fuel mix and vacuum advance/timing.
Instead of some shop doing it, how about just having one of your own? Pretty simple to install too. Comes with everything, even an exhaust pipe bung for the 02 Sensor. Love mine. I always know what my engine is doing. Whether it's at idle, coming on the secondaries or 6K RPM.
I've learned a few things that my Chevy SBC, runs pretty rich when cold, then leans out as it warms up. I rejetted my Holley, based on the readings (really lean at idle, but crazy rich at RPM and this is a brand new carb from Holley.
Sits nicely on top of the steering column. Very sensitive, real time info.
$178.00 and an easy afternoon's install (plus getting the bung welded in the exhaust, I got charged $25 at my local muffler shop, ten minutes max).
Is there any chance that your fans are running in the correct rotation? Shot in the dark!
No, they are setup correct as puller fans. Its the dewitts dual spal system.
Just road tested with air dam extension, 102*, 30 minute ride up the hill topped out at 220*. So 20* cooler with the air dam extension. I think the issue is airflow.
Im considering ordering an extra air dam, taking it to a metal fabricator and having them make me a pace style aggressive air scoop... does anyone make a performance air dam/spoiler for these cars? I cant imagine it being possible to cool a stroker motor or more with this stock configuration anywhere that it gets hot (like phx).
Do the fans cover a large portion of the radiator and is it the CFL of the fans move enough air across the radiator? I know DeWitts makes good cooling systems, but it might not be moving enough air over the radiator.
if you have a shroud with the fans make sure they have vents otherwise at speed the air backs up (cant get past the fan)causing heat issues
Any lower hose collapsing? (due to wrong radiator cap)
taking a high pressure water hose to the backside of the radiator and condenser does make a difference youd be surprised how many of those fins get plugged with debris
Sounds like youre getting there!
Hey guys, thanks for the tips. The condenser was already cleaned/degreased, and the radiator is a brand new dewitts with dual SPAL's. Their system has vents that open on the SPAL's at high speed to allow air through. The shroud basically covers the whole back of the radiator. My understanding is this is the best system money can buy to cool this car, and it did help a lot vs. the stock radiator and clutch fan (I was getting to 260+* with that setup, I'd have to pull over and turn the car off!)
The lower hose isn't collapsing in the garage at high rpm. There is no spring in it, but it's a firm hose. I can't even find a lower hose with a spring in it, every place I called in town said they haven't even made those in 20 years. The only thing they said I could do is use one of those ugly steel hoses. I don't think it's collapsing. It's just really hot in phoenix and with A/C on driving uphill the car get's hot...
The main problem appeared to be airflow, adding the air dam extender and sealing the top of the radiator dropped the temp by 20*. I've got it maxing out at 220* now during 102* weather with A/C on driving uphill for 30 minutes. I honestly think better radiator seals and some sort of performance cowl to scoop more air through the radiator would do the trick, but I haven't found anything aftermarket I can add to it. Only thing I can think of is to have a metal shop fabricate something for me...
Amazing. You've got the best radiator and fans money can buy and it's still overheating. Meanwhile, my built up L48, with a $150 Chinese aluminum radiator and $40 junkyard Camaro V6 electric fans runs no more than 200 degrees ever. And now you believe that you to fabricate a metal spoiler extension to make it work?
Amazing. You've got the best radiator and fans money can buy and it's still overheating. Meanwhile, my built up L48, with a $150 Chinese aluminum radiator and $40 junkyard Camaro V6 electric fans runs no more than 200 degrees ever. And now you believe that you to fabricate a metal spoiler extension to make it work?
No idea why this reply had to be laced with sarcasm, but I was able to deduce that you think my car should not run at 220*, in 102* phoenix weather, driving up a slight incline for 20+ minutes, with the A/C on. I have nothing to compare it to, so you may be right. With the air dam extension, even over 100* otherwise it runs right at about 205-210 on flat road, 180-190* in stop/go traffic.
So what is your theory on what the problem is?
Another couple of things to mention, I'm not sure people researched the motor from my first post. The Jasper Performance crate motor I have installed is a 300hp motor with slightly larger pistons and an upgraded cam to get the 300hp. I have an edelbrock performer intake, performer carb, headers with no cats and flowmaster 40 mufflers. I've been told that the more HP you try and get out of a sbc 350 the hotter it will run. Again, I have nothing to compare it to, this may very well be normal for this motor as far as I know. Anyone else running a similar setup, or even a stroker motor in Phoenix, Vegas, or similar climate to compare it to?
If possible compare the fan output (cfm) on a newer Camaro or c6. The Spal set up you have might not be moving the volume of air that a fan set up on a c6 or Camaro electric fan moves. You know where the problem is, now getting the fix.
that you think my car should not run at 220*, in 102* phoenix weather, driving up a slight incline for 20+ minutes, with the A/C on
That will put the real test to any cooling system it gets brutally hot out there. last time I rolled through there at 1am it was 112!!! Rolled down the window on I10 nearly took my breath away
Thinking more and more the comment about the factory fans on Camaros, Trucks may be where its at. If they can cool them with AC on towing in hot climates why couldnt they keep a simple vette cool?
Personally might look into some Silverado fans I think.
The brushless ones look real nice too less of a hit to the system.
No sarcasm, but you're the first C3 owner, I can recall, who's doing air dam mods to supposedly get more air flow through the radiator. I would also like to ask how are the fans hooked up electrically? I had to install an auxiliary fuse box in my '74, because I had too many new electrical demands on the stock fuse box. Is the electrical demand for the fans being met? Just for reference, I'm located in the High Desert of SoCal and we get triple digits all summer long. Finally, if you look how the engine compartment is set up on a C3 Corvette, it's a box that's sealed all the way around the top, with no way for the heat to escape, except through the bottom of the car. Not a good recipe for keeping an engine cool. I actually put a pair of hood vents on the top of the hood to let some of that hot air escape.
And I'm still advocating an Air-Fuel Ratio gauge. You might have had it checked out in a shop on a smog dyno with an Exhaust Gas Analyzer in the tail pipe, but the closer you are to the exhaust header, the more accurate it is. If its running excessively lean or even rich, it's going to make a huge difference in how much heat the engine is putting out. Unless your car o,ecomputer controlled, a good A/F ratio gauge on a carb'd car is a must have. Also, I've got serious heat shields on my exhaust system by the engine. It helps to cut the engine compartment temps down.
05-07-2016, 07:25 AM
, I discovered that my overflow tank for the coolant is right behind the license plate, basically blocking a lot of air that would flow up to the air dam and get kicked into the radiator. I can't find anywhere better to put it right now, but that might need a relocation to help even more.
