C3 - Radiator Overflow/expansion tank

[Greg F.]

I'm not very knowledgeable when it comes to the cooling system. I have a 71 small block. There is a hose just beneath my radiator cap. I believe its only purpose is for overflow, correct? Why do some of the the earlier c3's have expansion tanks and some don't? I had a small spot of antifreeze under my car. It was directly beneath this hose located beneath the cap. I just had some work done, and antifreeze was added. I'm guessing this was the cause. Thanks in advance for your reply.

Greg

[Joe L.]

Re: C3 - Radiator Overflow/expansion tank

Greg-----

The hose you describe on a 71 was for cooling system overflow. Coolant will purge from this hose under a variety of conditions and is normal. One condition that wil almost always cause purging is if the surge tank (for cars so-equipped) or the radiator, itself, are filled too full.

All 1953 through 1972 Corvettes used this sort of system. 1973 was the first year that Corvettes were equipped with a coolant recovery system. The coolant recovery system eliminated overflow to the atmosphere. All Corvettes thereafter were equipped with coolant recovery systems. Why didn't they do this earlier? Why didn't they do a LOT of things earlier?

[Jack H.]

Re: C3 - Radiator Overflow/expansion tank

Cooling system specifics vary with engine configuration. In 1971, the base engine SB used a Harrison aluminum radiator with RH inner fender mounted aluminum expansion tank. When heat producing options were added to the car (automatic transmission, A/C), the radiator changed to a Harrison brass radiation sporting a larger heat dissipation profile.

The brass radiators had internal expansion space and the RH tank generally had a 'FULL' line embossed on it to indicate the general fill level. So, a discrete external expansion tank wasn't needed with these radiators.

Typically, when shops work on a car's cooling system where drain & refill is part of the job, they intentionally OVERFILL the system to thwart air bubbles trapped in the system that will naturally 'burp' their out during initial engine operation. They should advise the owner to expect some minor excess coolant dump from the overflow tube for the first 1-3 engine heating cycles as the system find its 'natural' fill level, but often they don't mention this because they're familiar with the process.

What you don't want to do is replenish coolant that's 'puked' out and let the cooling system seek/find its native fill level. BUT, if the system expells a LOT of coolant or continues to dump coolant after a few engine shut down episodes, it's time to be concerned...

[John H.]

Re: C3 - Radiator Overflow/expansion tank

Joe -

They didn't do it earlier because the coolant recovery system was covered by a patent issued in the mid-60's to an independent inventor, and GM couldn't come to terms with him on licensing/royalties, etc. Finally GM just went ahead and incorporated it in production anyway in 1973, the inventor sued as expected, and the suit was eventually settled out of court.