Thanks Graham and Jonmac - The after market tank I got has an overflow tube
that feeds down to the road. Before I got the right cap I would drive until
the engine was starting to overheat and then pull off to the side of the
road, open the hood, remove the cap (after it cooled down a bit) and then
pull up the overflow tube and blew on it until the radiator refilled. My
wife, and anyone else watching of course, thought that I was looney.
Bob
> Hi Bob
> The Rad cap is also described as a PVRV, or pressure vacuum release valve,
> you have the big rubber seal that makes to the bottom of the filler neck,
> this deals with the pressure relief and in the middle of this is the
vacuum
> release valve with a very soft spring on it, the pressure of the spring is
> just enough to make a seal, as the pressure rises it presses on this disc
> and pushes it closed. As the coolant expands it lifts the whole lot to
> escape. As the engine cools the pressure diminishes and then becomes a
> vacuum, this is sufficient to allow the air pressure acting on the coolant
> in the expansion bottle to push the coolant back up the hose and push open
> the vacuum release cap an return to the rad, any leak in the hose will
allow
> air to enter the system in preference to the water.
> All the Triumphs I have except the Dolomite (which uses the pressurised
> header tank principle) have this coolant recovery system, and it works!
> How to tell, make a mark on the expansion bottle after a refill and then
go
> for a drive, when you return with a nice hot engine, open the bonnet and
> switch off the engine, the coolant should be some level higher than the
> mark, watch as the engine cools and you will see the coolant start to be
> drawn back in. Chances are it will only draw back 75 to 90 percent of the
> amount that was expelled during warming, this is due to differences in
level
> and efficiency of the system.
>
> Hope this helps!
>
> Graham.
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