1988 ,150 mercury runnung hot

[easygoing]

the temp, guage allway shows over heating ,alarm is sounding after about half hr of running seams to cool down at about 3500 rpms, been doing this for years ,have changed every thing, water is shooting out of piss hole

 

[easygoing]

may be a bent propeller blade

 

[racerone]

Blown / leaking head gaskets will cause overheat.

 

[easygoing]

have replaced head gaskets,guage,sending unit popit valve, engine seems to run ok, i disconneced the alarm was driving me crazy

 

[faztbullet]

Have you checked the t-stats?

 

[guyjg]

If one or more of the spark plugs look like they were steam cleaned it could be a cracked cylinder.

 

[Texasmark]

There should be a water hose running from the top center of the block over the rear and down below the block. At the bottom should be a cover with a couple of screws. Under the cover is the popoff valve that is in charge of cooling at higher rpms. It is larger than the stats and allows more cooling water to flow when open. Sounds to me like yours is not opening as required and/or is clogged. On the smaller engines it is supposed to open at around 2500 rpms.

HTH,
Mark