Overheating 7.4L Yamah I/O 1992 260 HRS

[tburrous]

New to Boating<br /><br />I try and run engine once a week for 10 minutes to charge the batteries and circulate the oil during the winter here in Washington. However, today after placing water muffs over the intakes on the out drive and starting the engine, no water was being expelled form the exhaust exchange at the bottom of transom. So of course the temperature rose over 180 degrees. So I have three questions. First, how is water being sucked from the intakes on the out drive through the exhaust system? Second, this engine is fresh water-cooled but requires heat exchange from water coming in the out drive, how does this work? Third, I don’t have the out drive all the way down, it’s about half way down when I run the boat out of the water, is this possibly the root of my problem? I’m thinking of taking the boat to the lake and running in the water to see if the problem persist. If it still overheats what should I check for? <br />

 

[Trent]

Re: Overheating 7.4L Yamah I/O 1992 260 HRS

TB... Iv never worked on a Yammie outdrive but Iv got a good friend that does all the time. He is a dealer and would be glad to help you out. If you cant find your problem e-mail me at Trentcr@hotmail.com and I will foward his e-mail address or phone number to you.

 

[its-a-sweater]

Re: Overheating 7.4L Yamah I/O 1992 260 HRS

TB,<br /><br />I assume when you say that your drive is fresh water cooled you mean it has a closed cooling system?<br /><br />If thats the case the water from the drive is circulated through a tank called a heat exchanger. Most of these heat exchangers are long cylinder looking things usually mounted on the top front of the engine.<br /><br />The things I would look for are. 1. Does the coolant in the closed cooling system look contaminated? 2. Is the thermostat opening properly just like a car.<br />3. Has something changed meaning is the temp. now higher.<br /><br />The system should be relatively simple. You have a raw water pick up pump that circulates water to the heat exchanger and an engine circ. pump that circulates coolant through the engine.<br /><br />Is the boat parked somewhere that critters can crawl up into the drive?