90 2stroke overheat. T-stat, water passage questions

[brian3006]

So just bought an early 90's 90hp 2-stroke. first trip out with it, overheats almost instatly when I brought it up to speed.. New water pump was installed and has a very strong pee stream. When the alrm went off the water coming out of the pee stream was pretty warm and the exhaust plate was hot. brought it back to dock and idles for a while just fine. motor was nice and cool. though maybe the t-stat just stuck but then opened. took it back for a second trip with sam results.
brought it home and took the t-stat housing off and removed the T-stat and pcv. a little bit of salt corosion but not too bad. cleaned it up and put it back without the T-stat. going to test it again tomm.

I obviously have some slight concern about salt/corrosion buildup in the water passages... when I had the T-stat cover off, I hooked up the water and started the motor. A good volume of water poured out of the holes.

Does this indocate anything regarding water flow around the cylinders or heads? How does the water flow through these engines? What excactly is the purpose of the PCV valve?

Thanks for any advice

[boscoe99]

The PCV (Pressure Control Valve) limits the amount of water pressure that the water pump can provide to the block. If and when the pressure gets too high the valve will open, bypassing water. Thus keeping the pressure from getting to high.

[TownsendsFJR1300]

IME, with salt clogged passages(head/cylinder, it'll overheat at higher RPM's (Not enough coolant flow thru the head) but at say half throttle, run fine.

Can you post about RPM it overheats? Also, is it consistent overheating at that RPM(roughly)?


The PCV releases excess water pressure. If stuck open, it can over heat(not keeping water up in the block).

.

[brian3006]

well unfortunately my tach is not operating correctly (old analog style) so RPM is a guess. Working on getting the multifunction gauges but $$$...... First time was at WOT though... Second time was pretty close to that as well. both times were pretty quick though.
I did test the old T-stat in boiling water. It did open but very slowly....

[99yam40]

to do it right you will need to remove head and exhaust covers and clean it all out.

or you can try circulating a mild acid or something called Rydlime marine descaler to see if that helps before having to pull bolts.

do a search on line to read up on it

hate to say it, but you should have test drove the motor before buying