You are not really looking for an absolute number anyway, just a
change from "normal".
The numbers you should expect to see are about 3 at idle, ramping up to about
17-18 at WOT.

tks, I did a little surfing elsewhere and I guess that the tell tale
is on the other side of some kind of pop it valve so if you wanted to
get closest to the water pump then it might be better on the side
where the spark plugs are. However, as you say all you want is to be
able to see an abnormal change (same with the temp gauge) to know that
something different has happened.

I'll play with it this weekend with a fuel pump gauge and then buy a
real water pump pressure gauge later.

tks for the comments.

don