Engine Temperature and Starting

[va3cgt]

I have a 2014 Tohatsu 30 hp that would not start if the engine was too hot. Why is it too hot, I suspect the impeller may be missing a few blades so I've ordered a new one. What happened to me got to our fishing spot, shut the motor down, then went to start it about 10 minutes later. I would crank fine but would not fire. I popped off the hood and the engine felt pretty hot. So I paddled to the nearby marine and left the boat over night. I returned the next day and the motor fired up right away. Today, same thing. I used the motor out front of the cottage, then parked it. An hour later I went to leave and it wouldn't start again. It would just crank and not fire. I popped the hood off again and decided to splash water on the fuel pump area to cool it down. After 30 seconds, the motor fired right up. So to conclude this is obviously a temperature related issue of some sort. The ECU detects high heat and prevents the engine from starting to prevent damage. But WHY is it getting so hot to begin with? Thermostat? Impeller? Or some other problem?

 

[Sea Rider]

That's a 4 strokes model ? don't think (probably wrong) that on portable models there's a heat sensor built on powerhead to shut OB down. The only way for an OB to overheat badly is if lower leg at speed caught debris, plastic bag, banana peel, you name it, and weren't aware of this situation going on at lower tail which has damaged impeller vanes due to running dry at speed..

OB should heat enough as not to burn your hand when crankcase is touched. Check water pump..

Happy Boating

 

[pvanv]

Is the model MFS30B or C? Year is irrelevant. No, the ECU is not designed to keep the motor from running if overheated. What temperature does the motor get to? Never change just the impeller; always do the complete wp kit, about every 3rd year in cold clean fresh water, or as frequently as annually in silty salt water. Was the vapor separator drained for storage last off-season? You are clearly under warranty, so see your local dealer.

 

[va3cgt]

Ah...vapor separator! That thing was hot as hell when I touched it. I splashed water on it to cool it down and the motor started, no problem. I'm pretty sure I drained it for storage. Why is that vapor separator such a problem? it's a NSF30B. Nissan...Tohatsu, same thing.

 

[pvanv]

There is a low-pressure fuel system that feeds fuel to the separator, which has a float like a carburetor. Inside the separator is the high pressure fuel feed pump, which pressurizes the fuel rail. In addition, there is the low-pressure filter, the high pressure filter, and the fuel cooler, as well as the air vent box that is fitted to the separator. Any of these parts could have an issue that leads to a hot soak restart problem.

Since you are under warranty, I would suggest you have your dealer look at it.

 

[va3cgt]

Interesting. I was looking at a sectional view of the vapor separator. Hopefully the replacement doesn't have the same problem in the future. Is that a design flaw with that part?

 

[pvanv]

Until you diagnose the issue, don't start throwing guesses and parts at the problem. Have your dealer look it over under warranty. That's why you have a warranty. No, all injected motors have that type of separator, it's not a design flaw. The only overheat issue I have ever has with the NSF/MFS25/30B has been on a long shaft model, when the motor was allowed to freeze with water in the driveshaft housing, collapsing the water tube. That resulted in a severe overheat, requiring a lot of new gaskets, thermostat, water tube, etc.