Are you sure? I checked the t stat with a small mirror. At the entrance of fresh water the t stat divides in 2 ways - 1) engine and 2) exhaust & upside the t stat. There is no possibility for cold water in the engine getting out to the exhaust. All fresh water have to go through the bypass to the exhaust - and its a small bypass....

For visualization in trouble shooting try 4 ea. Pieces of clear reinforced hose about 4" to 6" in length (from h/w store).
Put one side to t-stat lines and barb connect other end to factory hoses.
Now you can see how the water, is/is not, flowing.
"a moving picture is priceless"

I'm positive. Exactly as I described. I dissected one (cut apart) because I was having a water psi issue on the dyno with a motor I had set up full wet.

Sounds brash........do not doubt me on this one. LOL.

Sb,i know you are right, just giving op a way to see for themself how it works and see where water is/not flowing.
All of your expert advice is much apericiated by me and many others to be sure.
Thanks again.

I totally agree with the clear hose water hoses and this how we check a lot of cooling related problems - next is to buy different thin walled as well as thick wall clear hoses, The thin wall hoses placed in areas will expand showing possible too much water pressure if needing to check. and off course the thick wall clear hoses should be used on any part that has the suction side of cooling so hose does not collapse. Anyways just throwing it out there.

Could his thermostat/diverter spacer be in wrong?

Yes, especially if tstat is mounted under spacer instead of on top. That spacer provides warm and cold water direction. The t-stat provides hot water direction.

Also, the relatively small holes connecting the lower chamber to the top chamber (the exhaust water comes from the top chamber) are plugged (easy to happen because of size) this will cause water not to come out of exhaust until the t-stat opens.

So....chances are at this time, those smaller holes connecting lower chamber to upper, are plugged.

^^^^ Agree with this ^^^^ this exactly what I was talking about look for restrictions - T-stat and or the T- stat housing and or necks in post # 13.

YOU just explained it a whole lot better and in more details than I did

Okay, found pic of cold/hot water flow thru the Merc t-stat housing that I made years ago.

See post#9 here: http://forums.boatfreaks.org/showthr...t-stat+housing

I go on to describe it a little further.

I made a test drive yesterday. Now i read 17 PSI at 5000rpm and 0mls, 30PSI at 50mls and 35PSI at 70mls. No hose burst, but it´s a lot pressure. A friend has 22PSI at 65mls (WOT) with low water and the side pickup. I only have the lowwater pickup.