Radiator Caps

While doing some other work, I have found that the cooling system on my 328 doesn't seem to pressurize. The normal pressure build-up seems to be being vented by the small disc valve that is on the cap to allow coolant to return to the system. Since there is no overflow tank on these engines, it SEEMS to me that the proper cap should EITHER have no such disc at all OR the little disc should be lightly spring loaded closed as opposed to hanging open. If it's open, I don't see how the system can pressurize with a normal, slow increase in coolant volume that occurs as the engine warms up and the coolant expands.

I am using a typical 15PSI Stant cap. using this model cap since shortly after buying the car in '08 when a local "expert exotic" shop changed the coolant/cap. I've since replaced the coolant/cap several times but I'm now thinking the system hasn't been pressurizing for 11 years!

Any thoughts re proper Rad caps?

 

Sadly, just because I participated in the discussion doesn't mean I remember anything about it!

In reality, I just let the whole issue go until yesterday when I saw coolant draining from the overflow tube when the car was sitting in the driveway idling (at operating temp, fans cycling normally). I carefully opened the cap to find no pressure at all - the coolant had simply expanded to the level of the drain tube and was dribbling out via the open "dangling vent."

Despite the cost difference, I ordered a cap from Ricambi; I figure it HAS to be right - they've never let me down!

I referred to the cap as a radiator (rad) cap as opposed to expansion tank cap simply because it is usually the term used for them here (US) regardless of whether they actually cap the radiator or an expansion tank. Sorry for any confusion.

 

Yes, I know that my system was a bit overfull from my last coolant change so I am not surprised at coolant spitting out via the tube but that should only happen when the pressure exceeds the cap's rating, but since it was dribbling out with no pressure in the system, that's why I revisited this issue. Clearly, I have had the wrong type of cap on the car since the shop installed a new one at its first coolant change back in '08. I just bought the same cap whenever I decided to replace it, assuming they must have known what they were doing... And we all know about "assumptions," don't we?

 

I ordered this one: https://www.ricambiamerica.com/expansion-tank-cap-radiator.html They show a Stant available as well though it is a 1033. They don't show a 10231 or a 10230 for the 328 listings. It'll be interesting - should be here today since I specified 2 day shipping!

 

Thumbs up!! Ricambi cap works as the system requires!! I "tested" by doing the same thing as a few days ago. I "overfilled" the expansion tank so it was at the same level as it was when it was dribbling out coolant as it expanded to reach the overflow tube. This time - no dribbling whatsoever and when the pressure got to the point where it exceeded the cap's 1.1 bar, it spurted out of the overflow pipe for a few seconds as you would expect, rather than dribbling constantly. Tomorrow, after the engine is cold, I'll remove coolant from the tank to get it down to the correct level.

FWIW, though it's the same Ricambi part number, 137644, the cap does not look like the one in the Ricambi pic that I posted. It has a brass-colored square cap and a standard-looking disc valve that is spring loaded shut. It looks to me like the original style cap that is referred to in Ricambi's info:

** PLEASE NOTE, THESE CAPS (FROM FERRARI) NOW HAVE METAL 2 METAL EARS FOR OPENING, WHILE ORIGINAL PRODUCTION CAPS WERE SIMPLE SQUARE SHAPED VERSIONS. We do not have the old style caps available at this time **

So, since the square cap I received has the same Ricambi part number, it looks to me like they now have the original style caps but haven't updated the info.

And NEO...the bag is labeled correctly as "Expan Tank Cap," NOT "Radiator Cap!"

 

I've had 16 PSI (1.1 bar) caps since shortly after I bought the car in '08 but since the 'dangling valve' caps never allowed the system to pressurize, they were actually 0 PSI caps! Now I have a 16 psi cap that actually works.


Oh...forgot the best part about the Ricambi cap - a free pack of Chips Ahoy cookies!