1963 L76 overheating during cam break-in

[Jim B.]

I finally got a cam swap complete and now while attempting to get the recommended 30 minute new cam break-in run time at 2000-2500 RPM, she keeps getting hot and blows the antifreeze out. When the previous owner added Vintage Air, he also swapped radiators and the new one looks very similar but it does have a filler/cap where just the overflow pipe is supposed to be. During the past year I had the radiator pressure checked (twice). I've swapped caps with two others that were on running cars, removed the thermostat, and checked everything else I can think of. Temp gauge is either reading low or there is a big difference between the intake and the cap temps as at about 15 minutes of run time and 170 degrees, antifreeze blows all over from under the non-original cap (3 times). I replaced the solid lifter cam with a new CC hydraulic and have an initial 10 degree advance timing with vac disconnect. She starts right up and appears to run great except for the overheating problem in the garage that didn't exist before I swapped cams. Thanks for any help, jim.

[Richard G.]

Re: 1963 l76 overheating during cam break-in

First be sure to have the top heater hose off when you fill the motor. This will get ride of any are trapped in the system.
Remember, it the temperature sensor isn't under water the reading will not be accurate.
If you have access to an infrared gun use it to confirm the gauge readings.
That said, the fan clutch could be defective.
And lastly they all seem to get very warm when running at that high a speed (2000 rpm) and not moving.
I sometimes use a slightly lower rpm but always above 1500. This extends the run time but they still get hot.
When doing dyno runs they always use large fans in front of the car. You might try an addition fan if you have one.
When they start to overheat I just shut the motors down and let them cool overnight.
I run it again the next day till I get the time on the cam.
Best of luck
Rick

[Joseph S.]

Re: 1963 l76 overheating during cam break-in

Are you sure it is "overheating"? Have you checked with an IR gun while it is running. You say it blows antifreeze at 170 degrees. That is not an overheating temp.

[Edward J.]

Re: 1963 l76 overheating during cam break-in

Jim,check you radiator cap, make sure it releasing at the correct pressure as Joe says 170 is the normal running temp.

[Larry M.]

Re: 1963 l76 overheating during cam break-in

180 F will NOT cause the coolant to boil. Many of us run at this temperature with the cap off during coolant refilling, with no issues. Now 195 F may cause coolant to boil up and overflow the radiator or surge tank if you shut off the engine without the cap on. Depends on the concentration at that point in time.

Agree to replace the cap and also check the engine temperature with a good IR gun. Might want to also check coolant into and out of the radiator to see the amount of cooling provided.

FWIW: High resistance in the temperature sending unit wiring to the gage or in the firewall block due to corrosion or time will result in the temperature gage reading LOW.

Larry

[Brad Hillhouse (37766)]

Re: 1963 L76 overheating during cam break-in

You do not say if you are still using the original expansion tank. How is it plumbed into the cooling system? Are you using the overflow nipple which is protected by the radiator cap as the transfer balance hose to the expansion tank? Are you filling the system using the radiator cap on the radiator, or the expansion tank? The expansion tank was placed higher than the radiator for a good reason, to allow air to escape the system and you may be fighting the GM design with your cheapo radiator. Lots more to discuss but you may be fighting yourself with the use of a radiator design not compatible with the system. GM & Harrison spent millions of dollars on cooling system research that I would guess was not done by the aftermarket radiator company that sold a radiator that just fits the mounting holes.

Brad Hillhouse #37766

[Kenneth B.]

Re: 1963 L76 overheating during cam break-in

I had a problem with a engine that was toatly drained of antefreeze. It got hot after adding antifreeze & replacing the cap & it boiled over. Took the radiator cap off ran the engine till it quit burping coolent. There were air pockets stll in the block when filled & cap put on