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I hope everyone has a safe and productive 2021!  For those with major projects underway, let's try to get some of the 'hidden' deTomasos on the road later this year

I recently saw a FIM tank cap for sale (online somewhere!) and the seller claimed that it was an OEM Mangusta cap.  The same cap is illustrated in the top of the first image.  It's stamped with "FIM", "0,90" (bar) and "BOLOGNA".  Having looked through every image I can find, I have yet to see this cap on anyone's Goose.  Yet it makes that era FIM tanks were supplied with FIM caps, which came in a variety of styles.  Does anyone have a period image showing this or any other FIM cap in use?

Luckily an assortment of 'real' FIM caps and various repros (like the lower image) are available.  I understand quality varies but they are at least easy to find.

My car came with a round generic cap which I'm sure was a cheap aftermarket replacement installed by some well intentioned previous owner.  I'm now curious about its spring pressure and think it might have been responsible for damage to my coolant tank, which is unfortunately NOT readily available.  Here is the short story....

My tank always had a rough, soldered area on the bottom face where obviously something was not right (in photo 2 this solder has been removed but the area still has a solder film that marks the spot).  I finally took the time to separate the tank and see how bad things were inside.  I expected to find massive corrosion of some kind but found none.  Instead there were several small cracks (see photo 3).  Clearly these pierced through the brass and must have wept coolant.  The easy fix was to to glob solder on from the outside, which did the trick but looked bad.

So it seemed like a case of repeated over-pressure in the tank.  FIM caps range from 0 to 2.5 bar so clearly caps come with a wide range of spring pressures. An incorrect cap could clearly result in system over-pressure.  So no guarantees that's what happened to my tank, but I'm going to stick with 0.9 bar max from here and see if things hold together better.  Always something to find with these cars.  I have never heard of brass embrittling over time so hopefully that is not an issue.


Images (3)
  • IMG_0579: OEM FIM cap on top, repro on bottom
  • IMG_0580
  • IMG_0578
Last edited by nate
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I do not know the metric values as I have always used pound value caps.  To fascilitate the movment of coolant from the water pump to the radiator the lowest pressure possible is best. I use a 7 pound cap and have a heavy duty water pump.That raisess the boiling point by 14 degrees to 226.

People think that a high pressure, as used by NASCAR, 27 pounds I think, is better but that will cause internal resistance to the system.  The water pump pushes the coolant in a RWD car a very short distance compared to the Mangusta.


13 Pounds is about average for what cars used to have in the 70s. A very different system in the Mangusta.  Every pound of pressure raises the boiling point by 2 degrees. High pressure negates flow as it creates resistance, slowing the flow throughout the system

Much higher flow is available if you can use a lower pressure cap. A coolant recovery system will keep more coolant in the system, aid in cooling and also keep air out of the system that rots the hoses from the inside.

You could always show the car with the proper cap.  Remember that cars like the Mangusta were not "engineered" in the classic sense. They were a collection of available parts that had very little testing as combined.

Dick Ruzzin

Nate, must be the wavelength of our birthyear, I bought one on Ebay Italy a couple weeks ago...The engraved FIM Bologna may be real stuff, but search on a 246 at Mr. Fiat and one is new at $28...

I went for the 'all raised letters' that Denis shows (partly because the FIM Ghibli tank had the same look...the one at Maseratinet for the longest time). And yeah, like Denis, I have one (or 2 or 3 ) of the Lancia listed one....!

The cap with the MTA engraved is identical to one shown for a Maserati Biturbo. Pantera had raised letters but (as 70s ferraris) a different design (fim and Bologna at 12:00 and 6:00, not on the ears at 9:00 and 3:00)--Lee


Images (2)
  • ghibli tank NOS
  • fim tappo
Last edited by leea

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