[DeTomaso] Pressure cap question

David & Marilyn Bell davidabell at worldnet.att.net
Sun Aug 21 14:58:17 EDT 2011

I'm not familiar with the Cowboy from hell approach...

But on my car I removed the swirl tank and original overflow tanks
completely.  The outlet pipe from the block is connected directly to the
undercar pipe heading to the radiator using a short length of pipe with a 90
deg elbow on each end.  John Taphorn was able to source some aluminum
bottles with appropriate tap holes from Speedway (I think).  One of the twin
aluminum bottles serves as the reservoir tank w/pressure cap and is plumbed
into the suction side of the water pump.  The other bottle is the overflow
tank which is connected to the cap overflow on the reservoir tank (the
tubing runs from the reservoir tank neck to bottom of overflow bottle).  The
reservoir tank cap is 13 psi while the overflow tank cap has a zero-pressure

Most of these cooling mods were nicely documented in a very detailed article
by JT:

There are also a few pictures of my reservoir & overflow bottles here:

Dave Bell

-----Original Message-----
From: mike v [mailto:bluebugman2 at sbcglobal.net]
Sent: Sunday, August 21, 2011 11:14 AM
To: David & Marilyn Bell
Subject: Re: [DeTomaso] Pressure cap question

Hi Dave and yes I know about the American cap as I have installed a o-ring
to compensate the difference, I had everything dialed in last year but it
ran cold @ a high speed ( 140 ish) so I was told this ( installing  a33-180)
would solve my problems- well it never did just had overheating issue and I
forgot which thermo I used.

 So I think I have resolved the problem  using a Cleveland 180% stat,
drilled 2 holes in thermo, but now @ an idle I see coolant on the swirl tank
and of course the headers show signs of steam as it burns it away- I'm using
a #13 motocraft cap, I did go out & buy a #16 cap- so thinking it might be
bad or needs to go higher - to a #16 ?  what ya think ?

Dave you say that you eliminated the swirl tank and added a pressure/tank ,
would this be something like Cowboy from hell showed on the site or
something different ??

 I'm just getting tired of this unit overheating

thx Mike

----- Original Message -----
From: "David & Marilyn Bell" <davidabell at worldnet.att.net>
To: "mike v" <bluebugman2 at sbcglobal.net>; <detomaso at realbig.com>
Sent: Sunday, August 21, 2011 8:59 AM
Subject: RE: [DeTomaso] Pressure cap question

> First, if you still have a stock swirl tank, the original cap ring was not
> sized to mesh with stock American caps.  So American style replacement
> caps
> often do not seal properly.
> Second, the design of the Pantera cooling system is such that the swirl
> tank
> and pressure cap are on the high pressure side of the water pump (unlike
> most other vehicles).  So the spring cap has to deal with the normal
> pressure originating from the heat and fluid expansion of the coolant, but
> also practically all of the additional pressure generated by the water
> pump.
> At high rpm the combination of heat and water pump pressure can overcome
> the
> cap spring and coolant escapes.  The higher pressure radiator caps are one
> way to contain it, though I agree that very high pressures are hard on the
> cooling system in general.  Prior to reworking my Pantera cooling system
> and
> removing the swirl tank completely, I had to run a 22 psi cap to keep the
> coolant contained.  After swirl tank removal and addition of a separate
> reservoir/pressure tank, I run a regular old 13 psi cap and no coolant
> puking problems.
> Dave Bell
> -----Original Message-----
> From: detomaso-bounces at realbig.com
> [mailto:detomaso-bounces at realbig.com]On Behalf Of mike v
> Sent: Sunday, August 21, 2011 10:31 AM
> To: detomaso at realbig.com
> Subject: [DeTomaso] Pressure cap question
> Hi I was wondering what the pressure cap on the swirl tank should be as I
> have seen, read that is was between #13-16 caps but then I see on some of
> the Pantera site that sell parts and there saying #22 which is way too
> much
> in my opinion.
> I have a brand new motocraft cap that's #13 and when the motor gets warm
> it
> spurts out a small amount fluid, so either its bad or #13 isn't enough #
> for
> pressure
> thx in advance for advise
> Mike #7042
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