Yanmar 3JH3E fuel return

[MooGroc]

My 3JH3E is leaking a bit of fuel. I believe I've traced it back to the fuel return line that connects the fuel engine filter to the first of the 3 injectors. It looks easy to replace.

My questions are:

1. Can I replace it with generic fuel line hose or do I need a Yanmar replacement part?

2. Will I need to bleed the fuel system after replacing this fuel return line?

[Wotname]

1. Generic diesel rated fuel line is fine.
2. Not usually.

[transmitterdan]

Originally Posted by MooGroc

My 3JH3E is leaking a bit of fuel. I believe I've traced it back to the fuel return line that connects the fuel engine filter to the first of the 3 injectors. It looks easy to replace.



My questions are:



1. Can I replace it with generic fuel line hose or do I need a Yanmar replacement part?



2. Will I need to bleed the fuel system after replacing this fuel return line?

1) Maybe you should post a picture. I haven’t seen a fuel return line connected to a filter. If the existing part is a rubber hose then any diesel rated hose of the correct size will work. Get the correct type A hose that is USCG approved for engine spaces.

2) Yanmar 3JH engines are self bleeding. You will just have to crank it a bit more. Turn off the sea cock. Crank until it fires and immediately open sea cock. Requires two people. This is described in the user’s manual.

[model 10]

Are you talking about a steel line from the top of the injectors back the filter housing? It has almost no pressure so I suppose you could replace it with a hose. The ends are a problem, what are you going to use? I doubt it going to be 1/8"npt.

[Wotname]

^^ I have not worked on the 3JH but other Yanmars of similar size and vintage typically have steel return lines between the injectors (banjo bolts etc) and then use a flexible 5/16" fuel line from the last injector back to the return line discharge point which is sometimes an extra port on top of the engine mounted fuel filter.

The flexible fuel line is simply clamped onto hose barbs with simple hose clamps.

I never liked taking the return line back to the engine mounted filter, I always thought it was a potential air entry point in the fuel system so I ran it all the way back to the main fuel tank which was a lot of extra effort. I wonder at times if it was worth the effort or not and whether I was being unnecessarily over cautious.

[dfelsent]

Moonbeam’s return lines run to the tanks. A plus is that with valves set appropriately I can draw from one and return to the other. Built in transfer pump.

[model 10]

[QUOTE=Wotname;

I never liked taking the return line back to the engine mounted filter, I always thought it was a potential air entry point in the fuel system so I ran it all the way back to the main fuel tank which was a lot of extra effort. I wonder at times if it was worth the effort or not and whether I was being unnecessarily over cautious.[/QUOTE]

That is interesting. So on my Perkins, I could ditch the entire CAV filter assembly and run the injector return, right back to the tank return select valve? Guess I thought there was a reason for that line to return to the top of the filter housing?

[CassidyNZ]

My fuel also returns to the tank and I get to select which tank - I have two.

A question I’ve always pondered - given that the return fuel is warm, does the warming of the fuel in the tank have a tendency to make diesel bug a more likely prospect? I’ve only had the bug once in several years and like to think I took on dodgy fuel. But I sometimes wonder . . . .

[transmitterdan]

Originally Posted by CassidyNZ

My fuel also returns to the tank and I get to select which tank - I have two.

A question I’ve always pondered - given that the return fuel is warm, does the warming of the fuel in the tank have a tendency to make diesel bug a more likely prospect? I’ve only had the bug once in several years and like to think I took on dodgy fuel. But I sometimes wonder . . . .

Bugs need water to grow. Temperature doesn't much matter. Get water in fuel, get bugs.

[CassidyNZ]

Originally Posted by transmitterdan

Bugs need water to grow. Temperature doesn't much matter. Get water in fuel, get bugs.

Get warm fuel in aluminium tank in cool climate, get condensation.

Get condensation, get water in fuel.

Get water in fuel, get bugs.

My concern, exactly.

[transmitterdan]

Originally Posted by CassidyNZ

Get warm fuel in aluminium tank in cool climate, get condensation.



Get condensation, get water in fuel.



Get water in fuel, get bugs.



My concern, exactly.

Actually, get warm fuel in tank get less condensation I think. How many warm cups of coffee do you see with condensation? How many glasses of ice water have condensation?

[CassidyNZ]

Originally Posted by transmitterdan

Actually, get warm fuel in tank get less condensation I think. How many warm cups of coffee do you see with condensation? How many glasses of ice water have condensation?

No, I believe it’s the other way round. Warm air contacts cold surface and moisture in the warm air condenses. Go breath on a cold window, check the result then breath on a hot window and compare.

Even better, take the warm cup of coffee of which you speak and place on window sill. The iced water in a glass is doing exactly the same - condensing moisture from the warm air around it.

[transmitterdan]

Originally Posted by CassidyNZ

No, I believe it’s the other way round. Warm air contacts cold surface and moisture in the warm air condenses. Go breath on a cold window, check the result then breath on a hot window and compare.

Even better, take the warm cup of coffee of which you speak and place on window sill. The iced water in a glass is doing exactly the same - condensing moisture from the warm air around it.

Whatever...

[MooGroc]

So I removed the hose and inspected it. It didn't look like it was cracked or leaking so I put it back. Before replacing it, I measured the nipple onto which it fits. It was 4.5mm so I'll try to pick up some fuel line to have in case I later realize it really does need to be replaced.

I tightened the clamp on the line bringing fuel from the tank then ran the engine. The engine started without needing to be manually primed. After a few minutes
a drop of fuel showed up under the filter again. The filter was about due so I replaced it and pumped the little priming lever with the priming bolt cracked. It started and ran.

So far no leak. Maybe it was the filter. On too tight rather than too loose I suspect. I'll need to motor for a few hours to really know if the problem is resolved.

BTW, I'm constantly impressed by how much this 3 cylinder engine vibrates. The mounts look OK but they are 10 years old.

Thanks for the advise.

[Compass790]

Originally Posted by Ecos

That is interesting. So on my Perkins, I could ditch the entire CAV filter assembly and run the injector return, right back to the tank return select valve? Guess I thought there was a reason for that line to return to the top of the filter housing?

Yes you can run return line back to tank. Earlier model Yanmar ys8 series had the return line going to the filter but latest model had it going back to tank.
I,m curious, why do you want to get rid of your Cav filter assembly?