perhaps have the guy google 'coolant recovery pressure cap for
automotive cooling systems,

then maybe he'll believe coolant expands, such a cap accomodates
expansion by putting the 'extra' in overflow tank , then sucks it back
during cool-down.

cars have used this basic system in one form or another since the 70's ,
even a little earlier.

( rather oddly, my 1985 Mercedes car still uses the old fashioned system
..the air space at the top of the rad is the expasnion zone for
coolant..no overflow / recovery tank. )

re last comment below ..
all cars have some form of a pressure relief cap.
Haven't heard of a totally closed one yet,
though modern car cooling system pressures can be quite high.

here's a whole google search page the guy could read ...help him a lot I
imagine.

in one of those they mention 24psi for a more modern car.
Our vans run in the 13 or 14psi range max I believe.

I have not found the blue caps to be extra reliable. I always carry a
spare.
for example...
saw one Subaru engine conversion with a head gasket issue ..
after problems with the first cap and pressure tank,
they put on a new blue cap and pressure bottle.

pressure got so high...and the new blue cap did not release pressure,
that the pressure bottle puffed out like a football.
I still have it, it's only slightly warped where the level sensor screws
in ...
so new I hate to just throw it in landfill.

scott

On 04/26/2016 08:20 AM, Dan N wrote:
> Neil,
>
> he said that he gives room for the coolant to expand... I told him when the
> coolant expands the blue cap will open and the coolant goes to the
> expansion tank behind the license plate...
>
> he didn't buy it...
>
> I am sure he's thinking as modern car with the radiator and a filling tank
> with no pressure cap and no expansion tank..
>
> haha...
>
> :-)
>