2009 Tohatsu 20hp - Oil Cap Melted

[Lark40]

I was running my boat through a bunch of hydrilla weeds at low speed, when I saw a lot of smoke coming out of the motor. The red warning light was also flashing. I shut the motor off and dunked the hot cover into the water to cool it. The yellow oil filler cap had melted and blown off and was rolling in the cowling.

Luckily, I still had a good oil level, and was able to stuff the still-pliable cap back into the block threads to get back to the dock.

Apparently the weeds blocked the water intake, and the motor overheated. Is it normal for the oil cap to melt?

I plan to replace the oil cap and the impeller. What else should I be looking for?

 

[pvanv]

Re: 2009 Tohatsu 20hp - Oil Cap Melted

That was a pretty severe overheat.

The motor got so hot that the oil got so thin (and the clearances got so large) that you were below safe oil pressure. Anything that is plastic or rubber that is attached directly to the block is suspect at this point, and probably should be replaced -- or at least inspected very closely.

That would include the breather nipple on the starboard side of the block, as well as the water hose on the port side, and possibly the dipstick. Heck, you may have cooked the base gasket of the oil filter for that matter. Possibly also some of the plastic throttle linkage bits. There's also a real possibility the the thermostat is warped, so it may not work correctly or reliably in the future. The crankshaft and cam seals probably had some of their useful lives taken away as well. Hopefully the driven gear for the cam timing hasn't gotten distorted. It goes without saying that an oil and filter change is called for.

Best thing to do is to have your dealer go over the entire motor with a fine-toothed comb. I have only seen one motor that had gotten that hot. The owner had "broken in" the motor on the bench before installing it on the boat. Because it's a 4-stroke, he knew he didn't need to add TCW-3 oil to the gas... but he forgot that he still needed cooling water. Ugh.

I was able to get him working again with only a new water pump and a few external parts that had melted. With some luck, you may come out of this OK as well.

 

[TOHATSU GURU]

Re: 2009 Tohatsu 20hp - Oil Cap Melted

I know of one case where an idiot in Texas was running his 3.5 engine in mud and melted the cap. He was an idiot for saying that he didn't run the engine in mud, when inspection reveled that the water pump was completely clogged shut with the stuff

 

[pvanv]

Re: 2009 Tohatsu 20hp - Oil Cap Melted

So, I explained to my customer that he didn't break it in... He broke it. He understood. Interestingly, these Tohatsu 4-strokes seem to survive a lot of this type of abuse, and often can be revived back to useful condition. Pretty tough little motors.