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'79 radiators are ~18" so there's no way it can be a 20" fan. What's the make and model of the fan? Something I learned from reading Tom DeWitts posts is that 4 rows don't mean that much. That Champion has (4) .63" rows = 2.5" of total row width which is the same as some aftermarket 2X1.25" row radiators. I'm not knocking it, plenty of users here run it with great results.
OK so if your fan is the one I think it is it's only 1600cfm which isn't enough. Call the vendor and see if the Spal upgrade will bolt to your shroud. Spal is rated at 2024cfm (25% more).
I looked for ratings on champions site and couldnt find anything so I wondered about the rating of the fan also.
Originally Posted by Scott Liggett
Lot's of good suggestions here for checking the cause of your overheating issues. Especially, confirming timing and actual engine temps with a separate mechanical gauge. One thing not noted is that the factory location for the temp sending unit on these Corvettes is right between two exhaust ports in the head. One of the hottest places in the cooling jacket of the heads.
Does your Corvette still have the chin spoiler? If it is broken or missing, that can cause these engines to run hot. It is there to direct air coming under the car up into the radiator because of the lack of any real grille. 3rd Gen Camaros were also notorious for this problem.
Have you checked your upper and lower radiator hose for temperature differences? The upper hose should be at least 30 degrees hotter than the lower radiator hose. The radiator is a heat exchanger and the temps need to drop from one end to the other.
Double check the thermostat was installed correctly. Right side up. The spring side goes into intake manifold. Also make sure it isn't drilled with a bunch of holes. This may sound stupid, but the thermostat is there to control water flow through radiator. It also controls the speed the water flows through the radiator. If the water isn't in the radiator long enough, it will eventually overheat. Radiator is heat exchanger.
Also check water flow through radiator. With the cap off, you should see the water move slowly when thermostat is closed, then move much faster as thermostat opens.
Make sure you are running the correct spark plugs. The wrong heat range spark plugs will create excess heat in the combustion chamber and can engine to run hot. I believe the factory plug is an AC Delco R45TS, a pretty hot plug already. If you have some kind aftermarket type plug, like an E3, make sure it has the correct heat range.
Timing. Too much or not enough timing will cause overheating. Get a timing light on it. Make sure timing at idle is set with vacuum advance disconnected and plugged. Also, make sure timing is advancing correctly with timing light by revving the engine. If the mechanical advance in the distributor is not functioning correctly, the timing won't advance and overheating will occur. The springs and weights are under the cap and rotor and easily checked for binding or damage. Factory timing on these Corvettes is about 8 degrees before top dead center at about 600 rpm. They run better with about 12 degrees.
Not all electric fans are created equal. I know this from personal experience. Run a name brand electric fan. Spal or Derale are the best. Others make a lot of noise but don't move much air. Two smaller fans often work better than one big one. I currently run two Spals 12" inch 1800 cfm's on my 65 Impala, it never runs over 185*, even in desert heat.
Also, check to see if the fan is turning in correct direction. There are only two wires, wire them backwards and they run backwards.
I have a similar fan setup on my car using a volvo fan, it comes on at 200/ off at 190 keeping my 406 below his temps intown. On the interstate I have od so my rpms are about 2100 and will drop to 185 with a 160 t stat and OP is about 1.5 hour north of me.
I’m running a 20” 5500CFM electric pull fan in my aftermarket aluminum shroud for the huge 4 row aluminum radiator. I removed the mechanical fan when this was installed. I have checked the gauge multiple times, I’m running a Wilcox resistor which allows me to control the OAMs going to it so i can dial it within a few degrees of the sender temp, i also purchased a Zip corvette sender which is the most accurate to stock there is. I also fabricated a shroud for the top of the radiator where there was so space so all air goes directly into radiator. I ran the car this morning when i was bringing it to the mechanic and it never went over 215* with the AC running so I’m thinking the extra air flow helped. I’m contemplating on installing 2 smaller but high CFM push fans on the front of the tranny cooler as well so it will be getting as much air flow as possible.
See pics Top of radiator Topof radiator
That looks a lot more restrictive of the airflow than the dual fan set up I'm using.......makes me wonder if it works against your effort rather than help. The fan covers very little of the radiator ( a lot less than the dual fans I'm currently using) and to make matters more worrisome........the shrouding covers so much of the radiators surface area so close that it looks to be working against you rather than helping.
Bottom line.....I like your radiator choice but I'd wager your choice of fan and shroud is a mistake that needs fixing.
This is the set up I have in my 65 Impala. 12" Spals 1800 cfm each. It will idle all day in 100+ temps and never get hot. As you can see, the shroud is just plain sheet of aluminum. When I road trip, the fans are not even on. I drove 1853 miles from LA to Central Nebraska with them off the whole way. The problem is not your shroud, it is your lack of decent fans.
Did you visit your mechanic yet to check timing and rich/lean condition?
Even with the pool noodle on the top (where your L82 dual-snorkel cold air intake would otherwise go), a lot of air is still bypassing your radiator. You should do your best to fill all of the gaps on the side, or buy the foam pieces from a vendor (it may not be a direct fit with your non-stock radiator, so you may still need to customize some foam).
If you really want to try an experiment, if you are going over 40 mph or so, you don't need a fan. With the foam, and the front air dam in place (that was a great suggestion to add the extension, BTW, it was made for your car), you can park next to the highway, remove the fan and what looks like a restrictive shroud. You should be able to blast up and down the coast with traffic and remain cool with no fan. Just put the fan and shroud back on to drive in traffic. That is if the other components of your cooling system are working. Others have already mentioned:
Water pump? Are you 100% sure it's turning in the correct direction?
Thermostat? Did you drill a small hole or two for a bypass so it is always a bit open? You can accomplish the same by leaving the heating circuit on (coolant bypasses the thermostat, runs through the coil under the dash, and reenters the water pump). I have a bypass loop in both of my cars that does the same thing, without adding heat to the cabin.
Hopefully it is as simple as a timing fix and re-jetting your carb.
I picked car up this evening after having headers installed and timing checked. Timing was set using Lars papers and is current sitting at 11 degree which is inbetween factory and Lars. The thermostat i had installed was from Stewart for their hi flow pump. I ran car for an hour tonight on the highway around 65mph with AC on. Temp was around 215* and didn’t fluctuate, i pulled off and ran around a couple of roads with light traffic and temp didn’t rise in stop and go. I put the noodle to see if it would make a difference and it appears to have helped. I’m going to now try and find a real
shroud to cover that gap on top. I’m not sure how to tell if it’s turning in the right direction, i had it installed by a very well known corvette shop in town so I would hope they would know what they are doing. I have the stock 2 inch air damn and think that’s my next move. I had the carb rebuilt recently
by JR’s who is a Holley Legend in FL. (Wasn’t cheap).
That looks a lot more restrictive of the airflow than the dual fan set up I'm using.......makes me wonder if it works against your effort rather than help. The fan covers very little of the radiator ( a lot less than the dual fans I'm currently using) and to make matters more worrisome........the shrouding covers so much of the radiators surface area so close that it looks to be working against you rather than helping.
Bottom line.....I like your radiator choice but I'd wager your choice of fan and shroud is a mistake that needs fixing.
I originally had two fans with no shroud and the guys at the corvette medics in Melbourne talked me into going with the big single and that shroud. I’ve always questioned if that was the right choice but they told me that the one big would cool all 4 rows with that shroud and that the two smaller were just cooling the two rows. I’m not opposed at all to changing the fan. They charged me an arm and a leg for that shroud and fan too.
X2 on the chin spoiler and double down on the 79 spoiler extension used on the 79 ONLY L-82's with heavy duty cooling due to the 78 L-82's high temps that the motors were running routinely and on the highway at high revs^^^^^^^^^^.
The spoiler extension above attached to the chin spoiler is an OEM GM 1979 L-82 spoiler extension that I bought in the late 80's from my local chevrolet dealer after learning and seeing the 79 spoiler extension on a 79 C3 L-82 at a car show.....it is the genuine real deal from GM
I love that spoiler, I’m going to try and locate one. You’re car looks awesome!
'79 radiators are ~18" so there's no way it can be a 20" fan. What's the make and model of the fan? Something I learned from reading Tom DeWitts posts is that 4 rows don't mean that much. That Champion has (4) .63" rows = 2.5" of total row width which is the same as some aftermarket 2X1.25" row radiators. I'm not knocking it, plenty of users here run it with great results.
OK so if your fan is the one I think it is it's only 1600cfm which isn't enough. Call the vendor and see if the Spal upgrade will bolt to your shroud. Spal is rated at 2024cfm (25% more).
I just measured and stand corrected, it’s a 15 spal fan. So I’m assuming it’s 2024 and not the 5500 i was told it was. See some pics of the fan and shroud.
I agree with a previous post Heads. I've got a crane cam hooker super comp side mount headers edelbrock intake quick fuel carb and world products heads. Original clutch fan and radiator. Run all day at 175 to 180 if caught in traffic has got up to 190 a couple of times but cools right back down when moving.
So, i installed the L82 spoiler like mentioned in a post above, Ecklers had i stock so i drove up Tuesday and picked it up. Re-calibrated temp gauge (was 15* off) now i have it set to 4-5* off for more of a safety note. Ran the car for 45 minutes on highway and through town and car got to 197* and stayed there the entire trip (AC Off). So i think my problem ended up being bad air flow to radiator. Thanks to everyone for all the tips, at this point I’ve done everything i can to that cooling system within reason so I’m glad to know it’s in the temp range I’m OK with.
One thing that I did not see posted in this thread is the importance to burp all the air out of the engine and cooling system.
Trapped air in the system can add to additional heat and restricted flow.
There are several threads on the forum about how to purge all air from the system.
You might get the temp down even more if you follow the procedure and get any trapped air bubbles out.
Sorry for the late post, but I just read the thread.
Last edited by OldCarBum; Aug 21, 2019 at 11:54 PM.
I add a few more comments here. Glad to hear the spoiler extension used on the 79 L-82's only from GM helped which it should. C3's are unique with the radiator on a 45 degree angle in the nose which compromises airflow through the radiator. All the late L-82's ran VERY hot for emissions and the 78 L-82's with AC were notorious for normal temps of 225 with no ac running and 235-240 on the HIGHWAY with AC on. The spoiler extension was added by GM in 79 to the L-82's to help with bringing down HIGHWAY temps where airflow was not adequate through the nose, compromised by heads and emissions that forced the temps high on their own. With that said, the spoiler extension brought the temps down a lot on the highway......as some of you have discovered. The radiator seals are somewhat important with brass/copper radiators but not crucial with high efficiency aluminum radiators.
The other point I will make which some may not like is that using the stock heavy duty mechanical L-82/AC multi blade GM clutched fan is actually quite good at keeping the L-82's cool and is actually free wheeling 99% of the time on my car, not locked, since the cooling system is so efficient with the dewitts radiator, Stewart high flow aluminum stage 2 water pump, no emissions, GM spoiler extension, and performance timing. Even with the rebuilt L-82 with 10.2 compression/AFR aluminum heads 425+ Gross HP 355, my temps NEVER go above 180 degrees (Robertshaw High flow 180 thermostat with 1 drilled hole, not 3). The fan clutch on the fan is the OEM L-82 one rated to lock at 195 which the engine never sees so the fan is always freewheeling BUT always pulling a moderate of amount of air through the radiator, most importantly at slow speeds, where the temps on my car are actually slightly LOWER (175) than on the highway (180), AND on the highway where the mechanical fan is always pulling/directing air to that 45 degree radiator (this point is important)
The other point is if your C3 is an automatic, you absolutely should have a double stack tranny cooler in the nose, with a mechanical fan, not electric, pulling air through that cooler and radiator at all times, especially at slow speeds.
Are electric fans more efficient and better at some speeds cooling C3's? Yes, but not in every circumstance, especially with a C3 for the reasons stated above.
Hope that helps!
Last edited by jb78L-82; Aug 22, 2019 at 06:43 AM.
they told me that the one big would cool all 4 rows with that shroud and that the two smaller were just cooling the two rows..
Originally Posted by Aarond
So i think my problem ended up being bad air flow to radiator. .
Radiator 'rows' are arranged left to right but are next to each other. 1 row is simply 1 tube going left to right. 2 rows is 2 tubes going left to right and 3 and 4. But the rows are next to each other. Regardless of the fan size or number of fans all rows are being cooled. Its not possible to only cool 2 of 4 rows. But, there's a catch. Rows are also 'stacked' A single 10" fan without a shroud will pull air across a 10" stack of rows. A 16" fan will pull air across a 16" stack of rows.
And thats where a shroud comes into play....a shroud will allow a fan to pull air across whatever the dimension of the shroud is 10x10 15x15 20x15 etc. CFM's are needed...doesnt matter how big a fan is or how many fans there are...no CFM's = no cooling.
Now do a flashlight test. In the dark (obviously) place a light in front on the radiator and look for light leakage between the radiator and support. Also, I'm curious as to how much CFM your losing through the louvered shroud slots. I get why they're there, to allow some airflow across the radiator at highway speeds but thats what 'flappers' are for. IDK.
I add a few more comments here. Glad to hear the spoiler extension used on the 79 L-82's only from GM helped which it should. C3's are unique with the radiator on a 45 degree angle in the nose which compromises airflow through the radiator. All the late L-82's ran VERY hot for emissions and the 78 L-82's with AC were notorious for normal temps of 225 with no ac running and 235-240 on the HIGHWAY with AC on. The spoiler extension was added by GM in 79 to the L-82's to help with bringing down HIGHWAY temps where airflow was not adequate through the nose, compromised by heads and emissions that forced the temps high on their own. With that said, the spoiler extension brought the temps down a lot on the highway......as some of you have discovered. The radiator seals are somewhat important with brass/copper radiators but not crucial with high efficiency aluminum radiators.
The other point I will make which some may not like is that using the stock heavy duty mechanical L-82/AC multi blade GM clutched fan is actually quite good at keeping the L-82's cool and is actually free wheeling 99% of the time on my car, not locked, since the cooling system is so efficient with the dewitts radiator, Stewart high flow aluminum stage 2 water pump, no emissions, GM spoiler extension, and performance timing. Even with the rebuilt L-82 with 10.2 compression/AFR aluminum heads 425+ Gross HP 355, my temps NEVER go above 180 degrees (Robertshaw High flow 180 thermostat with 1 drilled hole, not 3). The fan clutch on the fan is the OEM L-82 one rated to lock at 195 which the engine never sees so the fan is always freewheeling BUT always pulling a moderate of amount of air through the radiator, most importantly at slow speeds, where the temps on my car are actually slightly LOWER (175) than on the highway (180), AND on the highway where the mechanical fan is always pulling/directing air to that 45 degree radiator (this point is important)
The other point is if your C3 is an automatic, you absolutely should have a double stack tranny cooler in the nose, with a mechanical fan, not electric, pulling air through that cooler and radiator at all times, especially at slow speeds.
Are electric fans more efficient and better at some speeds cooling C3's? Yes, but not in every circumstance, especially with a C3 for the reasons stated above.
Hope that helps!
As always you are a wealth of knowledge. I greatly appreciate it!
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
For clarification, the Stewart Stage 1 pump uses original GM castings (see their website) that has a bypass. This means that a thermostat doesn't need to be modified e.g. drilling holes. The Stage 2 and above pumps do not have a bypass and therefore require a modified thermostat e.g. needs holes drilled.
I have never had a problem getting air out my cooling system. GM solved that problem for us with the overflow tank that can transfer coolant back and forth as needed and this will rid the system of entrapped air, if so equipped.
I still have my oem cooling system setup except for a Stage 2 pump and modified thermostat. Cools just fine but temps where I am rarely get above 90*F.
There seems to be a notion that overheating problems are corrected with aluminium rads and electric fans. Not so. I would however recommend an aluminium radiator but save your money on the electric fan setup. Just not needed on C3's. Quite a few guys in here will attest to this but it's not my money being spent for electric fan setups.
