Air Leak In Fuel Line ?

Ahoy All , for quite some time, I have had this problem.

My BCC came equiped with a Racor fuel filter, the older style with a plastic sight bowl .

After motoring continously for 24 hours or more, the fuel level in the sight bowl drops, and can eventually fuel starve the 3GM30F enough to make it quit running.

I suspect an air leak on the incoming fuel line, but haven’t been able to track that down and stop the leak.

Does anyone have a way to help me correct this problem ? Do I need to install an electric fuel pump ?

On another note , the Banjo fuel fittings connecting fuel lines to the fuel pump and then to the fuel filter, seem to always come loose and start leaking . I find that tightning them up every 5 hours is necessary when continuously running the engine , any ideas what to do to correct this problem ?

Maybe your two problems are related?

I dont suppose using locktite on the banjo bolt is a good idea is it - for fear of getting locktite into fuel system, but i defer to a more experienced mechanic on that one.

Have you checked out the fuel tank vent line? Maybe you’re developing a vacuum that the lift pump can’t overcome. How do you restore the flow to the filter/engine? How about cracking open the fill plug while running the engine and seeing if that fixes the problem?

Marty Chin has mentioned that the Yanmar 3GM30F is known for those leaks at the banjo fittings. I had the problem for many years. It helped to use annealled copper washers–get them red-hot and drop them in cold water. What has helped the most is using special Cu washers that have a very narrow ring of gasket-type material built in to them. This solution was suggested by the Yanmar dealer in NSW, Australia. The amount of loosening has decreased a lot (but not totally) since I started using the special washers.

Dan Shaula

Banjo fittings have two copper washers, one between the part & the banjo fitting and one on the outside of the fitting between the bolt and fitting. These serve as gaskets when the bolt is tighten. Tighten the bolt, hence compressing the washer, work-hardens the washer. Although most people use the washer several times. Each time the bolt is tightened, more work-hardening takes place.

Instead of buying new copper washers, anneal the washers as follows:

  1. wear eye protection,

  2. place the washer on a brick, stone or something similar,

  3. With the flame from a propane torch, trace the wash with the inner blue tipped flame in a circular motion,

  4. When you see, a bluish color “dancing” on the surface of the washere were the flame touches the copper, the washer is ready,

  5. With pliers, pick the washer up and drop it in cold water.

This process removes work-hardening and the wash can be reused.

Hope that helps,


Hi Ben, I too thought about using locktite, but haven’t tried that for the same reasons that you have.

Hi Dan , Gosh those copper washers with a gasket material inbeded in them, sound like a good choice, so just why couldn’t I make some thin NBR washers to use as replacements for the copper washers ?

You have another good point, no , I haven’t checked that flame resistive fine mesh little screen, in the fuel tank vent line, Ouch ! I will check that one out.

Hi Rod, T Y , for the copper annealing proceedure. Do you think that there is a limit as to how many times you could anneal those little washers ?


You wrote, “Hi Rod, T Y , for the copper annealing proceedure. Do you think that there is a limit as to how many times you could anneal those little washers ?”

The answer is “NO.” I never throw a copper engine washer away. I anneal them and reuse them. IDUNA’s Sabb engine is a single cylinder diesel. I annealed the head head casket (a big washer) and keep it as a spare.

This annealing process for copper washers is not my idea. It was handed down through the diesel age and passed to me to hand down.

On another note, I think about this forum and the recent fund raising drive. What we are discussing is exactly the reason we all need to support this forum. There is not a diesel engine parts supplier who will tell you about annealing copper washers.

Cheers and Fair Winds,


I always heard that they should be cherry red then into the water.


Indeed, a cherry red color but in daylight, one can not detect the color. The technique I outlined was given to me by an older mechanic who ran a small engine shop with his son. Besides the usual run of the mill jobs, their specialty was restoring/rebuilding old engines.