71 70hp chrysler overheating

[EM1]

Have a 70hp chrysler that was garaged 8 years ago because of overheating even after being worked on twice.$$$ Pulled boat out. Starts good runs good. Seems to circulate water ok at idle. No water coming out at about half throttle and faster when moving on the water. Put motor in trash can full of water. Seems to circulate water ok even at full throttle. Thermostat is good. Believe the impeller was replaced last time worked on and looks good. Compression good 140. Head removed and water ports cleaned water pick up system is clear. Stops picking up water on the move at half throttle. Two mechanics stumped.$$ Me too. Any ideas? Thanks!

 

[Fouled Plug]

Re: 71 70hp chrysler overheating

Where is the cavitation plate in relation to the bottom of the boat hull? Possible the water pickup is not getting a good source of H2O on plane.

 

[The Marine Doctor]

Re: 71 70hp chrysler overheating

Has this engine been rebuilt at any time?<br /><br />If so..RTV silicone is to be used as a replacement for a base gasket. Its possible that the inlet for the water is plugged.<br /><br />TMD

 

[EM1]

Re: 71 70hp chrysler overheating

Thanks for the reply!<br /><br />The motor had been rebuilt and silicone used however the head was pulled and head gasket replaced there was silicone in the water ports but was cleaned with solvent by mechanic. There is one place on the lower left of the block that is hot while the rest is cool. Heat sensor is on the upper right. Maybe didn't get it all? <br /><br />As far as the cavitation plate.. Water level at a plain is just below the plate. It is just barely out of the water. The water inlet is three inches below the cavitation plate. Crossed my mind the boat could be creating to much air in the water before it gets to the inlet? Cavitation plate is broken off straight with front of lower U instead of comming around to a point. Problem? <br /><br />The boat is a 73 chrysler conqueror with a 20in transom. Motor is a two piece lower unit (long shaft) The cavitation plate is about an inch below bottom of boat. Motor has been on boat since 73 first trouble with cooling was in 88. Makes no sense? What do you think?

 

[Kendegreat]

Re: 71 70hp chrysler overheating

Somebody with more knowledge can probably explain this better. I was reading my Seloc manual because My 70 hp is overheating. There is something on the bottom left side of my motor that is suppose to act like a thermostat and it said it is suppose to open at higher speed.. If not it could cause it to overheat. I'll have to go find my manual to see what it is called. I'm at work.
Ken