Big Block Over Heating

[Jon Thys]

I have a 1971 Corvette with a 454, 4 speed and 3.55 gears that I have owned since 1974. Recently the motor was rebuilt with a compression ratio of 9.5 to 1 and with a mild roller cam. The motor has a complete a MSD ignition system. The radiator was tested, a highout water pump and a Corvette fan clutch with seven blade fan was reinstalled. The radiator has a 160 degree thermostat with 100% coolant. Prior to the new motor the car never ran above 180 to 190 degrees. Now it runs at 210 degrees and can go to 220 degrees after exiting the freeway. It will cook down to 210 degrees within five miles. My concern is the car is running to hot and would appreciate any help in getting the motor to run closer to 180 to 190 degrees. Thanks for your help and insight.

Jon Thys

[Tom R.]

Re: Big Block Over Heating

Jon, you should never run 100% coolant. try a 50-50 mixture. Tom

[Stephen L.]

Re: Big Block Over Heating

How was the radiator tested? They may test for leaks but it could be partially plugged. Have you altered the timing significantly? Did you install a different temp sensor that may have a different calibration? Have you attempted to measure the temp with an infrared unit to see if there is a significant difference.

[Joe C.]

Re: Big Block Over Heating

Jon,

As stated above, you should NEVER use 100% antifreeze for coolant. It will not transfer heat to the radiator as well as good ole' H2O. Best heat transfer is with 100% water, so, the best compromise AFA corrosion/freeze/boilover protection is a 50/50 mix.
Next, remove the 169* stat and install a 180* (or whatever your engine calls for)thermostat. The stat only sets the LOWER limit of your engine's operating temp. It has no effect on the upper limit, at all.
Was your temperature sending unit replaced with the engine rebuild? If it was, then re-install your old temp sender, without using any teflon tape on the threads. A thin coat of pipe dope or other thread sealant will be OK.
That was the easy part. Now, lots of things were changed during the rebuild of your engine. Also, the engine will have a slightly higher amount of internal friction for awhile, until the rings and bearings wear-in. The timing "map" may have been changed if your distributor was changed/rebuilt, which could affect the engine's op temp.

Joe

[Mark S. Lovejoy]

Re: Big Block Over Heating

Jon,

You did not mention replacing the radiator hoses.

Especially the lower hose, it has a wire wound spring in it to prevent it from collapsing from pump suction. These springs often rust through or get crushed when removing the hose.

The symptoms are; the engine will quickly overheat at high revs and not have any problems at low revs.

[John O.]

Re: Big Block Over Heating

Hi Jon

I'm no expert but a radiator shop told me if you use 100% antifreeze, you will run the engine hotter. You need the 50/ 50 mix.. Plus as mentioned, use the correct thermostat

John

[mike mccagh]

Re: Big Block Over Heating

agree with responders opposed to 100% antifreeze. years ago i rebuilt our 427/400 and filled the cooling system with 75% antifreeze and 25% water. darn thing would heat up to 240 degrees. tried every thing i could to solve the problem. last thing i did was remove a head to be certain i hadn't put it back together with incorrect head gasket which might have been blocking head to case flow of coolant. when i pulled the head , there was about 1/4 to 3/8" thick coating of a jelly-like material surrounding the outside wall of the cylinder bores. the silicone containing jelly did a real fine job of "insulating" the cyl walls and retarding the transfer of combustion-generated heat from the cylinder to the coolant. flushed the block and heads and it ran cooler but not to my liking. when the car had about 300 miles on the rebuilt engine, and running hot(220 degrees), we got in the old girl and drove it to cyprus gardens(2000 mile round trip) . the following summmer, the 427 never got over 200 degrees. in retrospect, the jelly and a semi-tight rebuilt engine was the culprit. mike

[Chuck R.]

Re: Big Block Over Heating

Hi Jon,

When you cut the antifreeze, make sure to use only distilled water so you don't introduce "deadly" minerals into the cooling system.

Hope that's the culprit.

Chuck

[mike mccagh]

Re: Big Block Over Heating

PS; forgot to strongly suggest you flush the system with copious amounts of water before re-filling with the 50/50 mix. mike

[Rob A.]

Re: Big Block Over Heating

Jon,

You can check to see if the thermostat is opening up without removing it. Before you start the engine, feel the upper radiator hose, then after the engine starts to warm up, feel it again to see if it's hot from water flow through the thermostat.

[John H.]

Re: Big Block Over Heating

You mentioned you had an MSD ignition system - does the distributor have vacuum advance and is it connected to full manifold vacuum? If it's a non-vacuum advance distributor, that will contribute significantly to hot running, at idle, in town traffic, and at highway speed. Also, have you verified actual temp at the hose just above the thermostat housing vs. your gauge reading so you know for sure what the gauge is really telling you? Is your front lower air dam in place? Your car is a "bottom-breather", and if the air dam is gone or damaged, that will guarantee hot running.

[Nick P.]

Re: Big Block Over Heating

Jon,

When my 73 454 was rebuilt I had an overheating problem, your carb may need re-jetting after raising the compression.A lean running engine may run hot,to check pull the plugs.White tips/insulators indicate a lean condition.
Good luck.
Nick