Thread: 402 Big Block

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Hello, 402 Big Block. Temp gauge showing signs of overheating. Checked everything out only to find about a pint of coolant leaking from the overflow tube. Assumed it was the thermostat, and replaced with a high performance 160 degree thermostat.
It is running great and not overheating, however when I kill the engine the overflow starts dripping. Never had a problem before and just curious what is going on. Thanks to all!

First, welcome to CHR! Hope you find what you're looking for and that you stick around for a while.

It sounds to me like you may have over-filled the radiator a bit if your still running an overflow tube to atmosphere. When you shut down the residual heat in the block & heads will continue to heat the stagnant coolant, increasing the pressure in the system and burping past the cap spring pressure. If I were you I would first install some type of coolant recovery tank, where the overflow tube hooks into the bottom of the tank, and the overflow from that tank is from a standpipe near the top. That way your system will burp when hot, but as it cools it will suck back the coolant from the tank. You can then run the radiator totally full, increasing coolant capacity circulating in the system, and eliminating air from the system which is the cause of corrosion.

Next I'd look at changing out that thermostat again, to at least a 180F if not a 190F. Running at 160F is too cold to cook off the acids that build up in your oil, and also hurts your mileage. All of the newer vehicles are running 195F or even 210F for normal operating temperature, to kick their efficiency up a notch.

X's 2... what he said!

I would like to thank you for the quick response. I will follow your advise and install the overflow tank and thermostat as well. Again thanks for the advise and warm welcome. Let you know has it goes.

I would just like to send out a thank you to rspears and 34_40 for your advice. I installed the 22 ounce aluminum overflow canister. It was a tight fit, however I was able to mount it between the battery and the passenger headlight. Required drilling and tapping into the interior panel. Installed the 195 degree thermostat as well. She is running like a champ. Hope the feed back can help the next guy out. Again thank you!

Thanks to you for returning with an update and the good news.

I would also check the Pressure Cap, it could be weak or not big enough spring to keep the coolant from making it to the over flow tube.