tracing mystery fuel leak

I have a small fuel leak that I can't find on my port motor, a 240hp yanmar, 4LHA stp.

After we crossed from Tarpon Springs to Carrabelle a few weeks back, I found approx. 2 oz of fuel on the diaper under the motor. The run took about 10 hours at 2,800 to 3,000 rpm, which is a little better than 15 knots.

I've been trying to find the leak, so far I have run the boat at idle up to 1,800 rpm, and there is nothing. I'm afraid to run the engine any faster than that without a load.

the fuel was all on the inboard side of the motor, under the injection pump. No spray at any of the injectors, no leak anywhere that I could find. I let it idle for 20 minutes, nothing.

Thoughts?

Thanks as always,
Doug

I have used foot powder, the kind in an aerosol can, to trace leaks. Liquids leave tracks in it and it smells nice. Easy to clean up. And your engine won't get athlete's foot.

Dougcole said:

I have a small fuel leak that I can't find on my port motor, a 240hp yanmar, 4LHA stp.

After we crossed from Tarpon Springs to Carrabelle a few weeks back, I found approx. 2 oz of fuel on the diaper under the motor. The run took about 10 hours at 2,800 to 3,000 rpm, which is a little better than 15 knots.

I've been trying to find the leak, so far I have run the boat at idle up to 1,800 rpm, and there is nothing. I'm afraid to run the engine any faster than that without a load.

the fuel was all on the inboard side of the motor, under the injection pump. No spray at any of the injectors, no leak anywhere that I could find. I let it idle for 20 minutes, nothing.

Thoughts?

Thanks as always,
Doug

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I would look at the fuel injector pump. There is a habit of vibration working the banjo fitting loose. Mine was only seen when engine was running.

I've used the blue Scott paper towels for leak chasing. There is distinct colour change if something wet touches it which a white towel cannot do.

i ike the foot or talcum powder. I may try that next time to boot.

In FLA boat fuel is red died, off road (no road taxes) and white paper toweling works.

Most diesel fuel flouresces to some degree. Use one of those little UV LED flashlights in subdued lighting and you may be able to track down the leak.

If your fuel doesn't glow in the dark or if you want to check the whole system quickly, add a couple of ounces of tracer dye to your tanks, and a different color dye to the coolant system. It doesn't take much to pinpoint even the smallest leak.