Fuel in Oil

[Bus_Tours]

Good Morning all,

I have a Tohatsu 9.8 4-stroke on my boat. Tried to start it over the weekend, and for the first time, no go. Did the normal investigations and when i removed the oil dipstick I found fuel under pressure in the oil... It spurted out.

What should i replace to fix this? I've seen posts about the fuel pump, but does the fuel pump have access to put fuel into the oil system?

Not sure which version of this engine i have, no markings/serial on it, which is a bad thing. Have photo's of engine, if that would help.

Many thanks in advance,

James

[Ferryman]

I’m not familiar with that engine but that much fuel in the sump may be caused by a leaking fuel pump diaphragm. I’m sure you’ll get replies from people that actually know the answer!

[tinker]

For fuel to be in the oil it would have to get past the piston rings.

[beamishken]

Originally Posted by tinker

For fuel to be in the oil it would have to get past the piston rings.

Unlikely that much fuel gets past the rings on a good engine, far more likely to be fuel pump related

[A1an]

If I remember correctly the fuel pump on those engines is driven by the camshaft. Quite possibly a failed rear seal/diaphragm on the pump.

Easily checked by removing pump and blowing in the input and output spigots, if fuel/air comes out of the back of the pump it’s fubar.

[Fenlander]

A1an is correct if we're thinking of the engine with the fuel pump bolted to the rear of the engine block. Amazing to think it could have diverted enough fuel to fill and pressurise the crankcase.

[Bushrider]

Google for "outboard making oil"

[tinker]

Originally Posted by beamishken

Unlikely that much fuel gets past the rings on a good engine, far more likely to be fuel pump related

Failed seal on the pump and its driven from the block? i agree sounds more likely than the rings.

[neil.mccrirrick]

Oil spurting from the dip stick is normally a failed head gasket I’d be looking there tbh

[paintman]

Quick look at an ebay pic of the fuel pump on these suggests that the diaphragm is operated by a plunger operated from an eccentric cam in the engine.

If that is the case then I think the diaphragm has split & fuel is going into the engine as a result.

Seen this on old cars with the pump operated by a lever resting on an eccentric on the cam shaft. One Hillman Hunter had what was effectively black petrol in the sump! After draining & refilling with oil & a new fuel pump it ran perfectly with no long term issues.

Strip & check the pump before doing/worrying about anything else.

ETA Once you've solved the problem don't forget to drain & refill with fresh oil & replace any filter(s) there might be.

[neil.mccrirrick]

It’s the under pressure part that’s a concern. Leaky fuel pump diaphragm isn’t likely to create that much back pressure

[A1an]

Originally Posted by neil.mccrirrick

It’s the under pressure part that’s a concern. Leaky fuel pump diaphragm isn’t likely to create that much back pressure

Crankcase breather should deal with that. I’d be checking it’s not blocked or kinked.

[tinker]

Bus must have got lost, great support rib.net, boating..........we all love a problem or two.