engine overheating - need suggestions

[jdupree]

I have a 1988 Johnson 90hp.  I just bought my 170 about 1 month ago.  Have not put it in the water yet.  Motor runs great for about 5 minutes and then the heat alarm goes off and the motor appears to be hot.  The discharge stream is very good and the guy told me that he had replaced the water pump.  I just replaced both thermastats and that did not fix it.  Based on what I can tell the water is not making it to the cylinders to cool them.  The boat has a history of saltwater use.  My father in law told me to take off a metal plate and check the water passages in the cylinders.  He said that corrosion can build in these and block water flow.  Is this true

Anyway, the motor runs excellent and the compression is good so I feel like it could be something simple.  Hopefully there are some good mechanics in this forum.  Please let me know what you come up with.  Thanks alot.

[JimCt]

Pose your question to TMD.  He has gotten me out of trouble more than once.
http://www.themarinedoctor.com/cgi-bin/YaBB.pl

[jdupree]

Well, found out what the overheating was from.  The ring broke off the #1 piston and scared the cylinder wall :x Ofcourse now it is time for a complete re-build.  The guy that I bought this boat from also stuck me with a bad fuel tank which I am fixing to tackle today.  I guess in this day and age it is hard to trust anyone.  Anyway, should have a great 170 when I get done.  When I get the time I will post some pics of the 170.  The best thing that I can say is that atleast the boat was garage kept and it really shows.  The hull doesn't have a scratch on it and all of the original decals and striping look brand new

[John Jones]

It's a roll of the dice anymore.  Sorry to hear about the motor but at least you have a solid, good looking hull.  Good luck and keep us posted.

[JimCt]

Real surprised you didn't find low compression in that one cylinder.

[ddd222]

w/ a hull that clean if possible don't rebuild get new, will change your boating experience

[Mr. Osprey]

It could very well be the head gaskets and that metal plate.

I had a 13' Del Quay and it had a 35hp Johnson on it. When I was out using it, it overheated and I fried it. Took it home, popped the cover, and saw that I fried the impeller, gaskets, and cylinder walls. I took of the plate that covers the cylinder water paths and saw that they were corroded and was part of the problem.

Take off your cover, check the walls, your impeller, and yuor head gaskets to see if water is leaking anywhere. To be safe, go to a local motor shop and just get a new gasket. There relatively cheap and you might as well replace it while it's off.