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1978 Spider
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Discussion Starter #1 (Edited)
My radiator cap came apart...so I need a new one...already did the BB search and as usual, conflicting PSI numbers...so what am I to do?

I see 7psi and 0.7bar. most commonly mentioned. But they are not the same thing.

7psi = 0.5 bar
0.7bar = 10psi

Autozone lists two caps for my 78 Alfa and both are 7psi. I've seen posts from Centerline stating 0.7bar. Classic Alfa lists a 7bar/10psi square cap (my old one was square)

I would tend to not follow AZ on this one...

I have the overflow tank. supposedly from some posts this makes a difference? how or why?
 

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Euro S2 with expansion tank, 14lbs.
Earlier euro cars without expansion tank, 7lbs
 

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1978 Spider
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Discussion Starter #4
I would think the higher PSI would be for a car with no tank. Would not a lower psi dump into the tank earlier and then need to suck back?
 

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No, the 14lbs is definitely for the car with an expansion tank. All my 105's (earlier cars) has 7lbs pressure caps. The only one I have (and have now) with a tank is my '75 2000 Spider Veloce. It has a 14lbs cap. Check out Classic Alfa's site They say 7lbs on early cars to '68, but there's an anomaly in their post '68 car recommendation, as it says their cap they provide for post '68 cars is 10lbs. (Still greater poundage). I found that on an early car with no tank, (venting to the ground), if you use a higher poundage cap (14lb), if you unscrew it when hot, or even warm, it dumps a huge amount of coolant down the vent pipe. No such issue with a 7lb cap.That's with a car with a new radiator core, and well upkept cooling system.
 

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1978 Spider
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Discussion Starter #6
Sounds good. I currently have a spare cap on with an integrated temp gauge. It's 0.9bar, about 13psi...I'm probably ok keeping it then?
 
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