Excessive exhaust Yamaha F300

[A-K]

Yesterday I did a offshore fishing trip. While drifting and fishing we noticed more than usual exhaust coming from my Yamaha F300.

The color was the same and no unusual smells or oders. Engine temp and oil pressure was normal. And the engine preformed as expected.

Just the amount of exhaust was probably double or even triple what it typically is. I’m closing in on 700 hours so I know my engine. And this was the most exhaust it’s ever produced.

Im curious if anyone has experienced or knows of a similar situation.

 

[Efx]

I would start with the basics, is it burning oil? Maybe a stuck thermostat and not warming up?

 

[A-K]

I would start with the basics, is it burning oil? Maybe a stuck thermostat and not warming up?

Not burning oil. I checked that. Could be a thermostat.

 

[tomc585]

Water vapor?

 

[A-K]

I only use E-Free gas.

 

[tomc585]

I meant saltwater cooling water.

 

[mrtodds]

If all that's mentioned is fine, could it be environmental? What I mean is seawater temperature, humidity, stalled winds? Temperature differential and stalled or calm wind can cause one to notice the exhaust more so than usual. It's producing exactly as much exhaust as it always has per revolution and nothing else is wrong, I'd say it was this.

 

[A-K]

If all that's mentioned is fine, could it be environmental? What I mean is seawater temperature, humidity, stalled winds? Temperature differential and stalled or calm wind can cause one to notice the exhaust more so than usual. It's producing exactly as much exhaust as it always has per revolution and nothing else is wrong, I'd say it was this.

While these are all good points.

I don’t think environmental has anything to really do with it. While the wind was dead calm that day, I have lots of time with this combo. Something was off for sure.

 

[A-K]

After discussing this situation with a Yamaha tech I’m going to change the impeller and spark plugs.

 

[Brent]

Something wrong with water pump?

 

[A-K]

Something wrong with water pump?

It’s making water but the mechanic thought it might not be pushing up all the way…but it’s due for one for one so why not.