[sailak]

I have a Yanmar 4JH2E. Curious if anyone knows how much fuel is returned to the tank? (And if anyone answers "all of the excess" I'll hunt you down and wind your furler backwards! )

The reason I'm asking is my boat has two tanks. I run mostly off the bow tank, fuel is returned to the keel tank. Just wondering if I need to be concerned about overflowing the keel tank with the return fuel.

Thanks

 

[albrazzi]

I would not return to a different Tank, it will overflow. The true rate of return has too many factors, line and pump size engine differences etc. it could be as much 95% or lower who knows. If you trust your Gage you can find out (sort of) but its tricky. A couple of three way valves can designate flow to and from individual Tanks.
I do fuel systems and Emergency Generators and its a big NO NO to mix Tanks. Plus the two tank tops may not be the same elevation and though unlikely you can get a negative siphon effect and overflow that way too.
BUT it sounds like you are doing it now, I don't know what the safety is but it would be good to know. Most systems return enough fuel to keep the fuel clean and "polished" with all that motion at sea. Yours may be designed with a much slower rate of return.

 

[sailak]

After thinking about it a bit more there is a return to each tank.

Thanks

 

[sailak]

I got a good demonstration of how much fuel is returned yesterday. We had just motored around a sheltered cove and I had just hoisted the main when the wife reported diesel in the cockpit! A steady stream of fuel was running from the keel tank vent located in the starboard storage bin in the cockpit. ( why oh why would anyone think that is a good location for the vent). I was at first a bit baffled as to what was happening but realized I must have mis- selected the fuel valve on the return line. Shut down the motor ( quick impromptu opportunity to practice heaving to) and the fuel quit flowing. A check of the valves confirmed I was feeding from bow and returning to keel tank.

I am going to explore relocating the vent, truly the only thing I've found on my Crealock that I'm displeased with.

 

[MedSailor]

Having a vent the spills into the bilge is preferable to one that spills overboard if the USCG is watching.

BTW, my Ford Lehman returns fuel back into it's own circuit by way of a "T" fitting. I don't know if that's a modification you can do to other engines, but it's a feature I love. No return lines going back to the tanks and no mistakes selecting tanks. You might want to see if you can arrange this setup.

MedSailor

 

[chuck53]

Remember, the more fuel that is returned to the tank, the better polishing you are getting.

 

[TQA]

In line 'jerk' pumps and standard injectors return very small quantities. Think along the lines of a cup an hour.

Rotary pumps and pressure time systems like the Cummins will return significant amounts. I have never measured it but I would think in terms of buckets an hour.

Never played with the common rail systems, they were just coming in when I was getting out of the spanner monkey business.

 

[dragon lady]

For any given engine several factors determine returned fuel volume, engine speed, load, piping details and lift pump condition to name some.

If you really care to know what yours is it can usually be checked....get everything ready.... disconnect return line at a suitable point, start engine and flow fuel into a clean 5 gallon bucket, filling a clean "calibrated" container, say 1 quart size, and emptying it into bucket as you go. measure time taken to get a quart, you can work the rest out from there.

In my engines (Cummins 6B) it is close to a gallon a minute +/-

Returning to a T in the fuel suction line is generally not a good idea, main purpose of the fuel return is cooling...hot fuel leads generally to injection pump failure.

The returned fuel has passed through all your fuel filters, putting it back to the tank also helps clean up the tank contents.

You should always return to the tank you are drawing from, exception can be made if you are using the system to transfer fuel under close observation, or if there is tank levelling through some piping arrangement...but generally keeping tanks separate is a better option.

 

[aloof]

Returning to the tank also flushes out air. The T fitting sounds like a bad idea. But maybe there is some other way for the air to escape....

My Beta 38 returns a gallon per hour...maybe more.

 

[capt jgwinks]

My old Albin AD2 had the return line connected to the secondary filter, and I'm pretty sure that was the factory setup as it was shown in the manual. Boat had two tanks and a selector valve on the feed, it worked very well that way. You would think it would be harder to bleed the engine with that setup, an air bubble could recirculate through the system multiple times, but I never had a problem with that.
That engine returned very little fuel though, like a few drops per hour.

 

[capecodda]

I had a setup like this on my previous boat with 100 hp Westerbeke (or westerbreak as we affectionately called it). The manifold allowed for the user to separately select input and return tanks. Never messed this up, but always spent a couple of extra minutes after manipulating the valves checking I hadn't returned to the non-supply tank. Someplace on this site someone posted a manifold switch that had the right human factors to prevent this error (one lever, selecting both return and supply). Nice idea.

Never figured out how much was going back.