I have a 1988 150 merc. two stroke

[mmorgan]

over heating at full throttle. I have replaced impeller,t-stats x2,popit valve. can anyone help???

 

[racerone]

Blown head gaskets will cause overheat.-------Compression test may show that.

 

[guyjg]

If the impeller was not intact when you changed it then a chunk may be blocking water flow. Check the inlet screens for junk.

 

[faztbullet]

Is this the only speed it overheats? Is the alarm going off or some other way you determining it overheating? Was the old impellers intact? What did base and housing look like (warped,melted,discolored)?

 

[Docksidemarineservices]

Did you purchase an aftermarket water pump kit? Does the impeller have a bronze hub? If yes there is a good chance the hub is slipping inside the rubber. Merc parts only on this one.