I have never done it - never heard of it - of putting a pressure gauge on the tell tale hole.
In my mind, it seems like if you block the coolant water outlet, it may cause problems somewhere.
But that is just me. and, who knows what the acceptable pressure is anyway ??
I have never seen anything or any information that relates to the "coolant outflow pressure".
It only takes a few minutes to drop the foot and inspect the water pump and impeller.
Well worth the trouble to give you peace of mind that that part is in good shape.
An overheated motor is NOT something you want to deal with !!!!!
I think what EZ707 is saying is correct - when your motor is at idle, and there is only a trickle
of water coming out, it is "suspect" of a failing or failed impeller. Drop the foot, check it out.
And, to know the compression of each cylinder will also put your mind at rest.
Now, what I
CAN share with you is this ....... I rerouted my telltale water outlet from the
engine block up to the steering wheel so I could constantly monitor it.
(( if you have tiller steer, you could do the same so you can clearly see it while you are driving ))
This is my 1979 Johnson 25hp. As you can see, it is quite a bit more than a sprinkle on your fingers.
And, the motor is at the normal idle speed, in a bucket. Not ear muffs. So there is no external influence
of pressurized water from the garden hose.
