The Stovebolt Site Forums The Shop Area Engine Shop I work better under Pressure.

Some where along the line Chevrolet decided that they could boost the performance of
their cooling systems by operating them under pressure. 4lbs at first and then 7lbs and on
up. But the 4lbs limit is what I want to address here. The Zero pressure systems weak spot
was the thin brass cooling tubes in the radiator and heater cores and at about 8 to 10lbs
they start to distort. However, they will run at 4lbs just fine.

I woke up thinking about the original recovery systems for the AD trucks again this
morning. I get to thinking about these every few months and I might have ever posted
about it somewhere in the past. So check me out and see if my thinking is correct.

With the zero pressure cap you can put a puke tank at the overflow but there won’t be
any return vacuum for recovery so the only purpose that it will serve is to catch the
overflow. That means that you have to use a pressure cap, 4lbs being the only choice,
which releases at the given pressure and dumps the overflow into the recovery tank when
hot. As it cools down, the vacuum created sucks the overflow from the puke tank back
into the radiator as long as there is a trap built into the overflow tank.
Now I haven’t been fortunate enough to see one of the original overflow tanks opened up
but I am imagining the inlet tube just welded into the bottom with maybe a short stand
pipe to keep from sucking in any crud that may settle to the bottom and a vent/dump tube
welded in the bottom and extending all the way to the little dome at the top????? That
would vent the pressure and in case of a massive over flow situation dump it overboard.
If anyone has one of the original tanks that was rotted thru and you’ve seen inside of it I'd
sure like to see it. And I’d also like to see the bottom outside where the pipes are welded
into the tank.

Denny Graham
Sandwich, IL

Why do you need a pressure cap to make a puke tank work? If there is no other source for air to return to the system when the engine cools down, and the end of the tube is below the surface of the liquid in the catch tank, the coolant will have to siphon back into the system. All a pressure cap does is raise the boiling point, 3 degrees per pound. It helps if the catch tank is close to the same vertical level as the overflow so the suction won't have to lift the coolant very far to get it back into the radiator.
Jerry

Mornin' Denny! Wouldn't mind seeing a least a pic of the overflow tank myself. I had to look it up on my repro Chevy Accesories list for 1950 as I wasn't aware of that tank.Given that there are parts numbers for a pass and a truck, I would be surprised if many truck buyers even bought one as it seems an item a truck buyer wouldn't consider necessary in the AD era.
So,an original in any condition is probably hard to find now.

Just the oposite Drew, a lot of truck owners bought them because they asked a lot more from the
trucks than they did from the cars and overheating was a problem.
They pop up at swap meets every once in a while and I've seen several original ones at shows.
I don't know but thay may have galvanized the inside to prevent it from rusting.

DG

Denny,

Here is a thread where you and others discussed that tank.

Here is another discussion.

Must have been daj vu Tim, I thought I'd been in on some discussion a while ago, thks.

Denny G

I dont think a cap that isnt made for a closed system will work.

I'm running a original "puke tank" On a 46 that works fine with out a pressure cap. The old truck has ben run through the Ozark mountians reaching as much as 200 degrees and worked fine. Checking the coolent level each morning finding it about one inch below the filler cap. It has the original 46 cap with a new gasket . I've never seen the insides of the tank but I'm sure it's hollow with a over flow spout.

EDIT,,a pressure cap.

Neat. Now I know what to look for this spring!