radiator overflow sends out coolant after engine shutoff

[dmjlambert]

I have a stock setup of 350 engine, original 4 row radiator, fan with clutch and shroud. I top off the radiator and put the cap on, and take the truck for a drive for 30 minutes. When I get back, after I shut off the engine, coolant comes out of the overflow tube and forms a puddle under the truck.

I guess I was expecting any overflow due to expansion would have occurred on the road, not after I shut the engine off. Is this because the engine gets hotter after I shut it off, compared to when it is running? I just thought it was kind of funny.

[cpnbnanamn]

How old is the radiator cap?

[dmjlambert]

Damned old, probably the original. Do you guys like the original style replacement caps, or the kind with the lever?

[dmjlambert]

I pulled the radiator and had it tested and fixed up at my local radiator shop, and it is a newly rebuilt original engine and new water pump and hoses.

[Stocker]

That's actually quite common, especially if the radiator is fairly full. With a recovery tank and a new cap for a sealed system, there's no problem anymore. And the radiator can be kept completely full.

[dazza]

And I think you need to leave about 3" from the top when filling, not completely full(without recovery setup) if that may be how you filled it.

[dazza]

I just remembered something in regards to after shutting the engine off. When I recently broke in my new engine, I forgot to put a hose on the radiator overflow and that engine was hot! As soon as I shut the engine down I had a pristine engine compartment full of radiator overflow... what a pita to clean up. So I'm assuming when it gets shut down, the water is not flowing, it's not being cooled by the fan and has nowhere else to go. High temps or too much fluid in the rad.

[In The Ten Ring]

From what I have read on here, the fluid going onto the ground (with my truck) or into an overflow tank is normal. My truck just had a hose running to the bottom edge of the passenger side inner fender....I plan to buy or build an overflow tank.

[tommys72]

When the truck, or any vehicle is shut down it gets hotter as no air is flowing or circulation is happening. With no expansion tank, the antifreeze will end up on the ground.

[dmjlambert]

Thanks for writing back. Yes, I did fill it more than 3 inches from the top or the max fill line, so I was expecting it to spit out some coolant. I do have the hose running down the side of the radiator and out onto the ground. I don't have a pristine engine compartment, but nevertheless I don't need it making a mess. I will probably put an recovery tank on it at some point, I have one on my wish list, and I think it is a nice upgrade. I think it was just funny that it spit out the fluid after I shut off the engine, instead of while it was running. I think it is interesting that the coolant expands that much, 3 inches worth. It seems like quite a bit. When you're in the kitchen and boiling a pot of water from stone cold to 212 degrees, the amount of water in the pot does not rise a visible amount. Curious...

[Ironhorse]

The coolant "puking" out the radiator overflow after engine shutdown is completely normal for trucks and cars from that era and before. It does not do that during engine operation since the coolant gathering heat from the engine combustion is cooled while passing thru the radiator via the water pump and then returning to the heated engine. When engine shutdown occurs, the heated coolant no longer circulates from the radiator via the water pump and expands due to the latent heat. No where else to go other than out the overflow tube at the radiator opening.

That was prior to "Uncle" forming the EPA and a boat load of automotive laws and restrictions of manufacture. All the newer cars and trucks capture the coolant in a recovery type closed system which you can easily adapt to your truck. I did it on my '71 4x4 and plan to add the same type system to my '71 Chevelle. Not stock for the year of mfg. but keeps the floor dry, no sweet liquid for the family dog or cat to lap up and also keeps the radiator full with no air space. No air space equals more coolant in the radiator and the overflow which gives a larger amount of coolant to work with.

Your kitchen pot boiling the water analogy may or may not be correct. When you boil water with no lid it takes longer and the heated water emits water vapor which you won't normally watch for. If you were to place a lid on the pot and continue boiling at the boiling point the raised pressure of the heated water will escape thru the pot lid and make a mess on the stove. The radiator does the same unless using a recovery type system.