The Stovebolt Site Forums The Shop Area Engine Shop radiator overflow when shutting down.

hey there,
i have a 1962 chevy 261.it runs great, keeps temp around 150-160, but as soon as i shut it down after driving for a bit, it will overflow out of the radiator.the level of the water is just a little above the radiator fins.can i just put a bottom feeding catch can and not have to worry about it any more?
Thanks, Danny

If it is too full it will do that. I'm guessing that you replace what you lost on a regular basis. Let it go next time and it should quit happening.

a catch can is a good idea & you may need to replace your radiator cap. when you shut the engine down the water stops circulating & alot more heat is absorbed. a pressurized cap raises the boiling point & keeps the coolant in.
robert

Test out FGT's theory by driving the truck a few times, checking the level after it cools down each time. If you are running cool, theory seems quite reasonable.

The normal level in an A-D truck's radiator is about two inches below the top.

Be careful with putting in a high pressure cap in a 47-53 1/2 ton truck's cooling system. The standard radiator cap was 0 psi and some parts in the system might not handle a pressure cap. A 4 psi cap, as used in 54/55, might be OK.

im usisng a 4lb cap, and i havent been replacing what ive lost, just to see if it will stop.it just keeps doing it and lowers the level of the water to where i cant even see it.i just add water when it gets too low.im going to install a catch can as soon as this heat dies down.
Danny

I think you have made the right decision. Even with a 4 lb. cap, the coolant can be caught and upon cool down be pulled back into the system. I have a zero pressure cap on my 37 and a catch tank from the overflow tube to the tank. I can't tell you when I last added water, but I just checked it and the coolant is just below the neck of at the tank.
Another thing the catch tank does is allow the system to stay "full" from the stand point of not sucking any air into the system on cool down, providing you keep about an inch or two of coolant in the catch tank. Air in the system can cause coolant out of the overflow especially on engine shutdown. A good idea is to drill a 1/8" hole in the flange of the thermostat. That hole will allow the system to release any air without sending coolant with it out the overflow. I've done and it works well.

well ive already drilled the thermostat so i guess all i need to do is install my catch can. any good ideas for a homemade catch can?
Thanks, Danny

How about a 1 quart rear end lube plastic jug. Cut the tip until your overflow tube fits in it. Cut the bottom of the tube at an angle and run it to the bottom. It has a small handle on it to tie wrap it up to the radiator support.

Most ot the FLAPS have plastic overflow tanks in stock and most have a bracket that can be mounted up under the wind dam pan just under the radiator. Unless you get down and under it, you can't even see it.

I just used a antifreeze jug. Drilled a hole in the cap for the size hose I could slip over the overflow tube. I had to cut the overflow tube, was down to low, so I could get a higher position to add rubber hose and a place to mount the jug. I have gone through a few jugs, melted/cracked etc., but their free.
Like posted before, this would also work, "most have a bracket that can be mounted up under the wind dam pan just under the radiator".

Here's one for ya.

I like the 1-qt. rectangular metal cans that paint thinner, alcohol, etc. comes in. Solder a strip of galvanized metal to the can, paint it black, and a couple of sheet metal screws can mount it just about anywhere there's a flat spot. Keep the can as close to the level of the radiator cap as possible. The rubber tube from the overflow needs to reach the bottom of the can, or close to it.
Jerry

Jerry

a 62 would take at a 7lb cap + a 50/50 of water and a/f which would give your system a boiling point of about 250 degrees F. the holes in the thermostat may help. you may have a problem somewhere in your system as that is not normal for the application
ron
if you are using a 4lb cap and water your boiling point is 224 degrees F