Return Fuel Tip

[swampu]

I know this is very generic but remember to always check your return fuel line for clogs when diagnosing engine problems. I know its not a trawler but my john deere fork lift was not running correctly. After a lot of head scratching (I didn't get any fuel from the return) The return from the injector pump was clogged full of crap and it would make the engine stall like it was running out of fuel. Just remember to check your return line when figuring out whats wrong. Have a good day.
Paul

 

[Bay Pelican]

Thanks, might never have thought of that.

Marty

 

[hmason]

Perhaps I don't understand the process. I thought that fuel passes thru the primary filter, then the secondary filter, then thru the injector pump before it enters the return line. How does the return line fill with crap?

 

[swampu]

That is what I thought. On this particular jd the fuel goes from the primary filter and the injector pump has a overflow type release ontop of the housing that t's into the return line. My onan and detroit have a stand alone injector pump and the return come from the injectors. That is why I posted. I've never seen this set up but with the knowledge I've learned on this forum I was stuck on the return fuel. It worked out.

 

[Bay Pelican]

Return line issue. For some reason unknown to me, the supply line on my 135 hp Lehman is 3/8" whereas the return is 1/4". Given the mention of a return line plugging up I would now prefer 3/8" in both directions.

Marty

 

[psneeld]

From previous posts..Lehman's return very little fuel...I ran mine for 5 minutes and only got a drop out the return fuel line.

My Westerbeke only dribbles a tad more...based on this and many posts, I eliminated return lines to my new fuel tanks..I just plumed a new return manifold and the returns just return to the end of my main fuel manifold.

But good catch Swampu!

 

[Capt Kangeroo]

"I eliminated return lines to my new fuel tanks..I just plumed a new return manifold and the returns just return to the end of my main fuel manifold"

Being largely "diesel illiterate", on the face of it this seems like a great idea and would eliminate a lot of extra piping. I can't help but wonder however why they are not all plumbed back to the inlet side of the manifold versus the tanks. Is there a trade off or downside?

 

[swampu]

There are guys on this board that will hopefully chime in but I think the reason for the return to the tank is to dump the heat, return fuel is hot. If you kept the fuel in a continuous loop I would imagine the temp of the fuel would continue to rise. In my specific case what I read is the Roosa Master (type of injector pump) uses the ball valve to release pressure, dirt and water into the return line. The design of the pump places all the gov., shut down sol. and every other part inside the pump housing. I had so much gunk in there that I piped a small filter inline were the ball valve was so I could flush out the funk.

 

[psneeld]

One poster who said his boat was plumbed that way asked Bob Smith at American Diesel or was present at one of his lectures and said the return is so minor not to worry. They worked on a Lehman in the parking lot and no return line was ever connected to anything...just a few drips during the demo.

Not many diesels can do this...

That's why I TESTED both my Lehmaan and Genset before committing to the manifold design.

And yes it can be done...but the diesels with big returns return a lot of heat so it's either the tank or a fuel cooler...in those cases I think people elect the tank for simplicity....even many day tanks are too small to deal with the heat
.
additional.....just saw swampu's post and yes heat is often the issue.

 

[psneeld]

I figured that at only a pint an hour return for both main and genset...by the time it get's through 2 brass manifolds and both primary and secondary filters and I don't plan on running in the tropics in the summertime and I only run a single in a spacious engine room (low heat load) and the run from the filters to the fuel pumps....

I think I'm safe because of my type engines....

I'll bet it gets hotter in my Genset sound enclosure warming things up than the .75 gallons of warm fuel return adds....

 

[BobH]

I emailed Bob Smith about this issue a while back and he recommended at least 3/8" for the return. My 225s have three returns and he said that the one from the head returns very little and could be ignored when installing the Floscan system.

I'll get some numbers next time I'm on the boat but one quick test I ran after installing the Floscan showed 20gph at 1500 RPM forward and almost the same amount returning.

Bob

 

[neworleansrich]

My fuel manifolds let me choose which tank to return fuel to. Once while running a Westerbeke generator I inadvertently had the fuel return completely shut off. It ran, but I was wondering why it was smoking in a rather odd way. I don't know how much different engines returns, but it seems to be significant.

I also have always heard the returning fuel helps cool the fuel pump. Whether this is true or not, it seems the returning fuel lines are quite warm when I am running.

 

[psneeld]

I emailed Bob Smith about this issue a while back and he recommended at least 3/8" for the return. My 225s have three returns and he said that the one from the head returns very little and could be ignored when installing the Floscan system.

I'll get some numbers next time I'm on the boat but one quick test I ran after installing the Floscan showed 20gph at 1500 RPM forward and almost the same amount returning.

Bob

You are saying that 20gph is returning?

Even more amazing is you are using 20gph at 1500.....even if that way for both engines...

Maybe the 3/8 is recommended for the 225's but for a 120 it would be kinda silly based on the internal return that is 1/4 and maybe less with the fittings....

 

[psneeld]

My fuel manifolds let me choose which tank to return fuel to. Once while running a Westerbeke generator I inadvertently had the fuel return completely shut off. It ran, but I was wondering why it was smoking in a rather odd way. I don't know how much different engines returns, but it seems to be significant.

I also have always heard the returning fuel helps cool the fuel pump. Whether this is true or not, it seems the returning fuel lines are quite warm when I am running.

Well on my older Westerbeke 8kw...I had the return line go into a mason jar and after several minutes of barely a dribble..I concluded that out of the 0.9 gallons per hour it consumes max.....it could only be returning a quart or so per hour...even if wrong...at 0.75 gallons per hour which is what I figure a 75% load on the genset it might burn plus the return from the Lehman so call it a gallon per hour....that's 20 ounces every ten minutes...so that's a mix of return and cool new fuel...the new coming through 3/8 lines, return coming through 1/4 lines...that over 2 to 1 cool fuel versus hot fuel...so I really only need to drop the temp of about 7 oz worth of hot fuel before it mixes though a large surface area piping and filter system...

Nope..I don't think in my case heat is gonna be an issue compared to all the other issure like piping running right along side of and into the engine itself before the injectors....

I DON'T recommend my piping for all boats or makes of engines/gensets.... unless you are confident in the return fuel numbers and temps...pipe conventionally.

If I find I have an issue with my design...I will be glad to post it..not afraid to admit an error if one is made.

 

[Capt Kangeroo]

In my case, the fuel is returned through heat exchangers / coolers to the tanks so theoretically if heat is the main issue perhaps this mod could also work in my case. The reason I ask is I have a ridiculously complicated fuel system with six tanks (total 1000 gal) and lines running virtually everywhere. I would like to rip out the two 100 gal keel day tanks for additional battery space and simplify the entire fuel system while I'm at it. Not sure what the ramifications of loosing one ton of fuel midships in the keel will have on stability but that's a whole other issue I need to get my head around. The additional batteries should somewhat offset the weight loss.