Radiator cap

[CWO (ret) Gilles Aubé]

What is the proper pressure for a C15A radiator cap?
And if possible what is the part number?

[Harry Moon]

non pressurized I think. Mine is, maybe different with a later motor?

[Grant Bowker]

There are 2 numbers in the parts books;
for "first type" cabs 2039428
for "second type" cabs 594498
The above seem to apply from C8 to C60, but the C60X and other GM vehicles with the 270 cubic inch engines seem to have used (more than one) different caps.

One online vendor lists the cap for the "second type" cab as http://www.parts123.com/PartFrame.as...vrolet_Part_Co
They also cross reference to the following part numbers (without saying whose the part numbers are): 33001, 703-1400, 850901, RC10 and RC68
Another vendor at: http://www.chevsofthe40s.com/Shop/se...talog=RO&go=go says the RC-10 is an AC Delco part number.
I'm sure other vendors have the caps too.

[Phil Waterman]

Hi

You may be able to just go down to the local parts store and find one. The non-pressure is only one of the issues. The other is actually getting the cap to seal on the top of the radiator filler tube. Any imperfections on filler tube sealing surface will defeat the coolant recover. I have taken pressure caps that had the proper tabs to engage the filler tube, then removed the pressure portion of the cap by drilling out the rivet that holds it pressure releaf part, then cut rubber gaskets to get a good seal on the neck of radiator.

Cheers Phil

[Stew Robertson]

Got a question
What is the expansion tank for if there is no pressure
how does the coolant get into the tank with no presure
there must be some I would think
Stew

[Grant Bowker]

My understanding is that the tank is freely connected (no valves or pressure traps) to the radiator overflow and that any fluid that would expand and vent to prevent pressure buildup flows to the expansion tank (that is in turn vented to open air) so fluid moves due to expansion, but no significant pressure builds anywhere in the system and that as the fluid cools/shrinks and would try to create a vacuum (except that it is still vented to atmosphere) the fluid returns to the radiator to avoid creating an actual vacuum.
In other words, there shouldn't be any significant pressure (perhaps a fraction of a PSI) build up anyqhere in the system since it is all freely connected together and open to the surroundings through the vent in the expansion tank. Am I making sense?

[Phil Waterman]

Hi Stew

Your question about pressure is a good one, the purpose obviously of a pressurized coolant system is to raise the boiling point of the coolant and as with modern vehicles this only works to a point when coolant must be released as it expands. Without a tank it is lost with a tank it is captured to be drawn back into the engine.

The coolant recovery tanks, as seen on the left front side of many CMPs is to capture any coolant that is pushed from the radiator as the engine warms up. If the radiator and cooling system is air tight then as the engine cools the fluid in the recovery tank is drawn back into the cooling system. If every thing is working correctly it keeps the radiator completely full of coolant.

The tanks is made so that though the tank is vented the line from the radiator is at the bottom of the tank. The coolant recovery tank even helps condense the coolant out of the steam if the engine blows steam into the tank. There is a vent incorporated into the tank which is suppose vent the air/steam at the top of the tank. This only works marginally well as the photo of the result of a broken fan belt on the highway. In that case the over blew through the tank and out on to the ground. broken fan belt.jpg

One other strange problem that I had once was on my HUP was that mud wasps decided to plug the vent from the tank while building a nest. Next time I took the HUP out as the engine came up to operating temp. There was no where for the air in the coolant tank to escape, which turned the system into a pressurized system until a hose blew off.

The tank location up on the side of the nose has the advantage of being up in the air stream but it has the disadvantage of being out there to be hit by almost anything. The tanks on Chevys were relocated down under the fender to protect it.

Hope that explains the why.

PS looks like Grant beat me in responding.

Cheers Phil