omc 5.7 overheating

[downtime]

Have a 1989 omc cobra with 5.7, the engine runs a little hotter then normal. I was doing some maintance and while running the motor with the muffs on, the water started to pulsate in and out on the stern. It almost seemed that the system was blocked for a couple of seconds then opens up for a cuople of seconds,,water is still running through the system but this is not normal. The temp runs about 10 degrees hotter then normal. This pulsating is kinda wierd. Im not sure if it is the the impeller or a thermostate or?..Any advice would be appriciated..

 

[motox6]

Re: omc 5.7 overheating

sound like blockage, because that pulsating is probably cavitation (water not getting through the blockage. usually a bad impellor shows a constant gradual rise in temp until gone allthough you might have bits of the impellor clogging up your thermostat. Could pop that t-stat housing off and check for impellor pieces.

 

[crazy charlie]

Re: omc 5.7 overheating

The exhaust flappers will do that if they are sticking until a certain amount of pressure opens them.They are easy to check or replace.Charlie

 

[rybad]

Re: omc 5.7 overheating

If your boat is in the water, the easiest thing to check first is the thermostat. (Dont just check it.. replace it - they're cheap!)<br /><br />If that looks OK, then you may want to pull the boat out and check you pickup impeller (the pump is on the outdrive).<br /><br />The flappers are a little more difficult to check, you have to remove your exhause bellow coming off your exhause risers. The flappers will be just inside your "Y" pipe. If they need to be replaced, be sure to check the date of your engine, not the boat's year of manf. OMC changed the size of the flappers in 1989, and if you have a 1988 engine, they wont fit. (flappers are about $20 each)<br /><br />Good luck.