cwyates4

I've got a '75 model with about a 400 horse sbc that i'm having trouble keeping cool. It has a fairly thick core radiator, and dual eletric fans that run when ignition is on. On the highway, I'm seeing about 190-205 which is great! But, in town (not heavy traffic, never just sitting and idling) I'm seeing temperatures creep up to the 240 range, and i don't care for that. The heads are cast iron, so they shouldn't be harmed at that temp, but ideas on getting it to run cooler? And where did these guys run from the factory?

Grumpy 427

Well from what i have heard, these C3's do run warm. The problem is the rad laying flat for one, not a lot of airflow getting through them. Higher compression and advanced timing will cause an engine to run hot as well. i had an aluminum rad with twin 11" electric fans moving 3000 cfm of air on my BBC in my camaro that made 708 hp and i could keep it at 195 in the city.

Now my C3 i am rebuilding, has the stock 3 core rad, that has been re rodded and cleaned properly. Stock shroud, clutch fan water pump etc with a 180 thermostat. I added all the rad seal foam to the hood etc. so will see what it runs for temp? It is making 340 hp. 9.5.0-1 compression and about 36 degrees total timing. I guess the key is to get as much air flowing through the rad at low speed as you can.

Paul L

That's hardly a factory engine!

My 1974 NOM/195hp L-48 runs ~180*F at highway speeds and it will creep up to 190-200 in stop-and-go city traffic depending on ambient temperatures. The t-stat is 180*F and the coolant mix is 50:50.

7T1vette

If you still have the original radiator, it is probably limed-up by now. You need to have it boiled out or use radiator cleaner in it to get rid of the lime and improve the cooling capability of the fins. Also, it is likely that the original radiator shroud and seals are damaged, missing, or installed incorrectly and the fan is not pulling enough air through the radiator to cool it during idling or slow traffic. You may also have a non-functional thermostatic fan clutch so that the fan really does no work when it gets hot [like it should do].

jb78L-82

A little trivia here, my 78 L-82 4 speed ran when new about 225 as a normal operating temp, not the L-48's, which ran about 190 degrees, on the highway. In fact, in the 1979 model Corvette, GM changed the 12 O'Clock position on the temp gauge to read 225 instead of 200 like it did on the 78's because I believe the temp guage reading 3/4 of the dial on the 78's made owners really nervous, especially the L-82 owners. One of the biggest culprit of high temp on my 78 L-82 was all the emission's control equipment, the radiator, fan clutch, and water pump. When I removed all the emissions equipment and changed to a 160 thermostat the temperature dropped a lot. Further reduction in temperature was achieved with 2.5 inch true duals and flow through Monza turbo mufflers with shorty headers. Recently, I replaced the 4 core radiator with a Dewitts aluminum one and a Stewart Stage 2 aluminum water pump and a 180 thermostat in place of the 160 thermostat since the engine ran too cool! Also, in 78/79, the thermostatic fan clutches on the L-48 and L-82 were different-on the L-48 the clutch engages at 180 degress and on the L82 the fan clutch was set to engage at 195. The reason for the differences were that the L-82 with the high lift cam and generous valve opening overlap, especially at idle, would not pass the sniffer test unless the much higher engine operating temperature was achieved. The difficulty in passing emissions was the primary reason that the L-82 died after 1980, a year in whih only 5,000 L-82's (230 HP) were produced and only with an automatic, no standard transmission by then. My 78 L-82 runs about 175 now with a 180 thermostat and never gets hot in traffic-never! Temperature floats between 165-180 depending on the temp outside. Pretty amazing what all that emission junk on the engine did to the operating temperature all in the name of emissions. Cars today are completely different and run great with all the emissions gear and get great mileage but back then, most of the emissions hardware was added to engines that were not designed for all that stuff and it hurt performace big time and made the operating temperaures real high. Hope that helps!

Ironcross

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180 since leaving the factory, or day 1

PRNDL

That's odd. I thought the factory stat was 195 over a wide range of years. Not that it wouldn't or couldn't run cooler with a 180 stat, I just seem to recall factory was 195.

cwyates4

the radiator is an aftermarket and brand new, every thing under this hood is brand new. Tstat is opening properly, no leaks.

I'm sitting here thinking about the position the radiator is in from the factory, that basically makes part of the radiator unused. I'm going to keep a close eye on it the next few days, and if i see over 230 again, I'm going to do something, i just havent decided what yet.

Dantana

I had this problem all day long with my 4 core set up and mechanical fan. I tried everything- rad flush, different t-stat, changed the angle of the radiator itself, foam seals... finally I bit the buttlet and switched out to an aluminum DeWitts with the dual electrics and I have no trouble at all now. I also changed out my water pump... are you sure it is circulating coolant correctly? You also might have some cavitation caused by air in the system

Paul L

The 195 came on stream in 1975 along with the catalytic converter.

cwyates4

found the problem. Fan relay (custom setup) was melted! took it out for a spin, never above 195 in town!

Mashman

Actually, according to my 72 service manual, the 72's had 195's - not sure about earlier.

Mash

10caipirinhas

So why was the fan relay melted ?

IMHO you're not finished with the diagnosis yet.

TopGunn

My 75 with ZZ4 and with the original radiator and 180 deg stat would only get to 200 in city driving with the A/C on, normally stays around 190.
I've changed the cam and heads with HP about what you have still with 180 stat and temps are the same. I had to install a DeWitts for other reasons but the temps are the same with the DeWitts.
I had one heck of a time with air pockets in this system which lead to some cooling issues, it would climb like crazy to over 220, then dive back down to 180-190. Every time I drain the radiator I have that problem so I have to remove the stat goose neck and fill to the top with the front end raised up, install it and fill the rest of the way.

MotorHead

180 since dual 13 inch spal fans

lars

Advancing the timing helps the engine run cooler. Retarded timing makes the engine run hot. Hot engines can be cooled down by running more initial timing or by making sure the vacuum advance is correctly matched to the engine so you get more timing at idle and low speed.

Lars

Ironcross

Your right, I believe the 195 stat was introduced around 1970 in most of the cars regardless of the make...one of the early crude attempts at emissions control. Others were smog pumps, EGR valves, and ported vacuum to name a couple more...It was not unusual to have 210+ running temperatures.

cwyates4

I'm not really sure to tell you the truth...but i've tried to re-create the senario and have not been able to do so. I'm just thinking a faulty relay...strange, but possible.

And to topGunn: If you're having that much trouble with air pockets in your system...you might want to do a compression test to be on the safe side. I had this problem with another vette of mine for over a year, culprit ended up being a small leak in the headgasket, very small.

10caipirinhas

Thanks........just curious if you found anything else.

cwyates4

Not a darn thing. everything seems to be in check. Since i got the fans running, I've only seen the temps up high once...and that was after alot of in town driving, followed by a spirited burst, i got them up to 220, which is acceptable for extreme conditions.