[Healeys] Radiator cap with expansion tank.

[Harold Manifold]

Hi Simon,

The radiator cap needs to be one designed for a closed coolant recovery
system. While it will look similar to a standard cap, it will have two
rubber gaskets—one at the top and one at the bottom of the radiator neck.
When the cooling system pressure exceeds the cap's rated pressure (7 psi),
coolant will flow through the overflow tube to the recovery tank. As the
coolant cools, it will then be drawn back into the radiator.

There are two general types of closed systems: an expansion tank and a
recovery tank. Expansion tanks are pressurized and are not the best option
for a Healey. For a recovery tank, the hose goes to the bottom of the tank,
and the tank itself operates at atmospheric pressure.

The recovery tank from a TR6 is a good fit for the 4-inch round hole in the
support that extends from the scuttle to the frame.

Harold

On Sat, Oct 11, 2025 at 11:05 AM sbyers--- via Healeys <
healeys at autox.team.net> wrote:

> Simon, I have an expansion tank in my BJ8 using the original metal tank
> from an MG Midget.  I also have the stock 7 psi cap on both the radiator
> and the overflow tank and a clear “overflow” hose on the radiator neck to
> the tank.  The tank captures any overflow from the radiator and I can see
> the system operate with the clear tubing.  When hot, the flow is out to
> the tank and back into the radiator as it cools.  Excess coolant in the
> overflow tank can flow out to the ground through the tank overflow
> connection.
>
>
>
> Steve Byers
>
> BJ8 Registry
>
> AHCA Delegate at Large
>
>
>
> *From:* Healeys <healeys-bounces at autox.team.net> *On Behalf Of *Simon
> Lachlan via Healeys
> *Sent:* Saturday, October 11, 2025 11:32 AM
> *To:* 'Healeys' <healeys at autox.team.net>
> *Subject:* [Healeys] Radiator cap with expansion tank.
>
>
>
> Forgive another stupid question but it’s sensible to be sure……….
>
> Am I right in assuming(!) that, if one fits an expansion tank, the
> standard cap is moved from the radiator to the expansion tank and is
> replaced by a blanking(?) cap ie one which has no spring, no means of
> relief etcetc? Seem logical to me but logic has let me down before.
>
> Simon
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