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
Last edited by Denny Graham; 12/31/2011 3:36 PM.
