Faulty radiator cap?

My '82 308 has begun to make sporadic noise when fully warmed up. I warmed it today to check the oil level (from what I have read, the car should be run for 10 minutes to fully warm up, then the level checked as soon as it is shut off- please correct me if I am wrong as the level seems extremely low even after adding oil, although the pressure did come up to nearly the mid-range after adding oil). When the engine was fully warmed up the car started to spew coolant from the overflow container, and made a growling noise a couple of times, which I attributed to the cap popping open and closed. I have had no problem with overheating- the temp always warms only to the mid-range. After cooling, the level in the overflow container is extremely low (at most 1/2" in the bottom). Would anyone think that this could be anything more than a faulty rad cap? Is there anything special on an F-car rad cap (I assume not)?

 

I have not had much luck finding a replacement rad cap, and want to get the cap replaced and bleed the rad prior to taking it out. O'Rielly could not find a suitable replacement, as they could not cross-reference it, and NAPA near us has closed. Does anyone know where I can find a suitable cap, and what the store's stock number is?

 

This is the cap that I tried, but O'Reilly does not carry Stant, and does not have a cross reference for them. I will give AutoZone a try and hope for the best.

 

While replacing the cap had a positive effect, I think that I will need to bleed the radiator as the problem was not entirely resolved. A new problem popped up, though, that I hope someone can help with. The last few times out the temperature gauge sits low, then suddenly swings to near max (~110), sits there, and after a couple of minutes suddenly drops back to normal. This repeats itself every couple of minutes. To me this sounds like a thermostat needing to be replaced. Does this sound right, or does anyone think otherwise? Could it simply be air in the lines messing with the thermostat?

 

That was kind of my thought- bleed, drive, and if the problem persists I will look into it further. Assuming bleeding does not resolve the problem, does it sound like thermostat to you? Would that not be the next thing to check? And based on the parts reference, I would be looking for:

THERMOSTATS ( NOT CORRECT OEM)
VW GOLF / RABBIT 1980 REF
VW PN# 056121113A 180F
VW PN#05612111371 160F

 

I have heard varying opinions on checking the oil, even from Ferrari mechanics. The last mechanic (specializing in Ferrari) says to run the car just long enough to fill the filter, shut off, and immediately check the oil. There is no real consensus that I can find.

 

I went to AutoZone, as they have a cross-reference for the Stant 11229. I am not positive off hand what their part number is, but the cross-reference is in their computer.

 

I had thought of the fans, but could not see them correcting cooling that quickly. Am I wrong?