Honda 20HP

Why does fuel get into the oil? Have drained oil completely and made sure I only put in 1 litre. After 2 days of fishing and trolling oil level is well over full. It seems to raise the level by at least 300 ml+++ Any suggestions?

Inspect fuel pump for leakage.---------Thermostat installed and working properly ?-------Does primer bulb go hard when you operate it ? Might be carburetor leakage too.---------Do you leave fuel line hooked up and tank vent closed when motor is not running ?

Thanks for reply. IN the process of checking fuel pump. Confused about thermostat. How can fuel get thru it? Yes, primer bulb goes hard. No, fuel tank is taken out when not running. We are in a remote area of Northern Territory Australia and are fishing most days. We usually troll for about 6-7 hours each day. Have completely drained oil and refilled to correct level, after day of trolling, come back, let motor cool down, check oil again, and level is about quarter of inch above correct level and if we go 2 days without draining oil, the level is half inch above line. First noticed problem when oil came back thru tappet cover breather and spilled out into intake manifold after 4 fishing trips. Never had problem before, and at camp there are alot of people with 20hp Hondas and no one has had this problem.

all comments most appreciated. All assistance helps. Cheers, Ross

The fuel does not get through the thermostat, but if the engine does not reach normal operating temp.
the fuel does not burn completely and the residue deposits in the crankcase.
check your thermostat, this is a likely cause.

Hi rossrick,

Yes, as dark_star says, a thermostat that is stuck open will cause the engine to run cold and, in turn, be very inefficient at burning the gasoline it is fed. The vapor then gets shoved passed the rings and into the crankcase, causing the engine to "make oil". The resultant mix in the crankcase will indeed have re-coalesced gasoline in it and will smell like gas too.

But, what you are describing sounds more like a leak. The thermostat scenario takes a while to develop while you are saying that it happens in a couple of days of trolling.

I would not be surprised if you find that your fuel pump is indeed leaking under the valve cover. Make sure you check it by first priming the bulb and watch for seepage. If you don't see anything amiss there, do this: Use a screwdriver or something similar to repeatedly depress the plunger and see if it leaks during operation.

Good luck and keep that oil changed until you figure it out.

Reply to all.
thanks for all your suggestions. As I am in a remote area have had to improvise and become a "bush mechanic". Checked the thermostat and it opened in hot water and closed as it should, so all okay there. Was able to "borrow" fuel pump from another 20HP and troll with it for 3 days, gradually improved on each trip. (Had changed oil beforehand of course). Put my own fuel pump back in my motor and after 2 days of trolling oil level seems to be at correct level. Can only presume that the bore was glazed or rings were "carboned-up". Each day entailed a trip of about 35 km to the river mouth before trolling for 5 or so hours, so can only presume these fast trips have somehow helped correct the problem. So, at the moment motor is running fine and oil level is normal, the fish (barramundi) are starting to bite, so life is as it should be. Thanks again for all your help and suggestions. Much appreciated. Cheers, Ross

Hi rossrick,
Thanks for the update. I agree that the hard run up to your fishing grounds may have been the fix. Pretty amazing that much fuel could "sneak" past the rings and cause the oil level to rise in so short a time. Keep monitoring the oil carefully and let us know of any changes. Enjoy your catch. I hear that Barramundi put up one helluva fight and taste great right off the "barby"!