F90 4 stroke - fuel dilution - is it normal?

[searanger]

I have a 2006 F90 on my boat. The boat is used mainly for fishing, and I ***** with the F90.

I run out to the fishing grounds and ***** for a few hours, before heading back in. It probably amounts to 6 hours of running a 7-1200 rpm for every one hour of cruising at 4200 rpm.

I have noticed that the oil level in my engine will increase very slowly, while the oil turns a bit reddish from the dye in the marine fuel.

Thermostat is brand new.

I had a mechanic tell me that it is quite common for this engine to "make oil" under those conditions.

Motor seems to run very well.

Can anyone here please weigh in on this?

[ausnoelm]

I don't think I would call it "normal" but it is "common" it is caused by a few things, the most common is the engine does not come up to full operating temperature, or is run at low RPM way to much, or the prop is too big and will not allow full RPM. Change the oil, and when you are running to and from your fishings spots, give the motor some throttle, it will not hurt it and in fact your motor will thank you by not "making oil" this is of course assuming the motor is OK mecahnicaly!

[searanger]

Thank you for weighing in on this issue!

It may be that I am not running long enough at higher rpm to evaporate the gasoline that makes its way in to the oil.

I think that the prop size is ok - it will do over 5000 rpm at wot, but I guess I am am a bit too scared of rpm's - the engine is mostly run at 41-4200 when cruising to fishing grounds, and I hardly ever exceed 4500.

[99yam40]

I would think it should be propped closer to 6000RPM at WOT, but check out this site to see what they show.
Performance Bulletin Home

[ausnoelm]

I guess your dealer has made sure you do not have a leaking fuel pump or something like that?

[searanger]

I guess I should look closer at how the boat is propped - I am pretty sure it will hardly reach 5500 rpm with the current 13x19 prop.

The mechanic did have a quick look at the fuel pump and did not see anything wrong with it.