Engine overheating

[MacDaddy302]

Hi! I have a 93 OMC Cobra with a Ford 302. I just unwrapped my boat and started to de-winterized it. I reattached the outdrive and got it running. I noticed that no anti-freeze came out of the engine, even after it was warmed up. Then, after 5 minutes of high idle (2K?), i notice it is overheating. the gauge is rising to about 225, then dropping to 165. It keeps doing this, it will rise and fall every 30 seconds or so. Whats going on? This engine never got over 150 in the past. I was wondering if you guys could give me a direction to go in. I had a local shop winterize it for me in the fall (i usually do it myself but i had just started college.) I'd like to fix this myself (and know its done right) then to involve the shop.<br /><br />My first thought was the thermostat, but why would it open at 225 only to close at 165? Don't they usually just pop open?<br /><br />I also found that the impeller housing has a slow drip. Would this allow enough air in to mess with the temp that much?<br /><br />BTW, the overheating was happening in the driveway with the mouse ears/garden hose on the outdrive.

 

[MacDaddy302]

Re: Engine overheating

Forgot to add, I didn't find any external leaks, cracked hoses, or water in the oil.

 

[Alumarine]

Re: Engine overheating

I'm not a boat expert at all but having said that I'd check the thermostat.<br /><br />You suspend it in a pot of water and turn on the heat. Using a thermometer check out the opening and closing temps.<br /><br />good luck

 

[austin123]

Re: Engine overheating

Sounds like the thermostat to me.<br />Something else you could try, take out the stat completely then run the engine and check your engine temp does not go high. If it does you may have a blockage somewhere.

 

[Don S]

Re: Engine overheating

No more than the thermostat costs, just put a new one in and be done with the thermostat game. No since taking it out sealing it up with no stat to test it, then go get a stat and go through the process again.<br />If it's a raw water cooled engine and you run without a thermostat, the temp sender will see cold water, but the engine will actually have hot spots. Keep a stat in the engine at all times.

 

[Mahoney]

Re: Engine overheating

Impellor housing has a slow drip--<br />if this wasn't there last year I would open it up and check it. Could be that water was somehow trapped in there and cracked the housing.<br /><br />Thermostat is the easiest check, but I would be suspicious of drips anywhere that just appeared after a winter.<br /><br />225 degrees is suspiciously near a boiling point. maybe the temp sendor is sensing water temperature from water forced through the system from hose pressure(impellor leak indicating possible impellor malfunction) water reaches 225 degrees, boils off through cooling system and repeats.<br /><br />This is just a way out there scenario, but should your thermostat look ok, I would check that leaky impellor housing anyway.

 

[MacDaddy302]

Re: Engine overheating

Well, it turned out to be a really simple and stupid problem. The boat was far from the house so I had to use a few lengths of hose to reach it. Moved it closer and used less hose, no overheating now. I replaced the impeller and thermostat afterwards because it hadn't been done since i've owned the boat ( 3-4 years ). Thanks for the suggestions. Mac

 

[Wotknot]

Re: Engine overheating

Aha......another manifestation of the old law of supply and demand.

 

[vipzach]

Re: Engine overheating

Gotta love an easy happy ending!!!!