Saginaw PS - Sealed or vented caps

[AuroraGirl]

So I am under the impression GM always vented PS through baffling in the caps. that is how my newer cars do it, but maybe they still were in the old days but different ways.

I have here saginaw ps pump caps(no hydroboost) from the 79 down SAE fittings, pressed on pulleys and about 2 or 3 caps from 1980+ metric fittings, pressed on pulleys. All of them except one has a vent in the top of the cap. That one is also blue, for some god who knows reason. It came out of a 77 buick, teardrop pump.

The blue one is a straight through hole with a baffle under the lettering of the cap that keeps fluid in, contaminents out

the others dont seem to have vents or at least at least they dont let me blow air through

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[bucket]

Hmm. I've actually never noticed if PS caps were vented or not.

 

[SquareRoot]

Anybody else see a trend here?

 

[AuroraGirl]

Hmm. I've actually never noticed if PS caps were vented or not.

that pressure gotta go somewhere. im just trying to figure out where it goes if the cap is not vented or at least find the vents and clear em. a bad vent on my old car cavitated the fluid and blew return line off. 30 dollar ps cap

my old ford, which had saginaw, had vented cap like the buick

 

[Matt69olds]

The pressure change from temperature has to go somewhere. If the cap itself isn’t vented, I’m betting the shape of the fill tube has a place where the cap doesn’t seal tight.

 

[Matt69olds]

I’m guessing theses cutout area of the fluid tank are designed to vent pressure. That’s my theory

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[Backfoot100]

I think the cap is probably loose and allows the vent.
My cap is not tight at all. I give it a quarter turn which prevents it from coming off completely but its still loose.
I don't recall if my original 88 square was the same way or not. Maybe that's not how its supposed to be either. I really don't know. I had to replace the pump a couple years ago because it got almost unsteerable at idle speeds but no problems at all since then.

 

[AuroraGirl]

I have looked and scoured, bought two different new caps(need a couple) and i think i figured it out. a vented cap, one that baffles but is open through the stem, often is accompanied by an orange seal. When not, the cap is not sealed(so it can vent) but it might weep out with splashing, which isnt an issue as much on old tall reservoirs like the shorter reservoirs they switched to for cars in the late 80s and trucks in late 90s