Fuel flow questions

[Ray Rhode]

As part of my continuing program of looking for trouble I have noticed that there is no fuel flowing through the return line to the tank. There is not even a drop of fuel flowing after 3-5 minutes of full throttle operation or at idle.

Everything I have read says that the engine pumps more fuel than it can burn and that the excess fuel is continuously returning to the tank. I checked the return line fitting on the tank and the return line and there are no restrictions. Has anyone checked this on their boat? Any suggestions? The engine is the Universal.M-25.

One other item I found (I just can’t leave bad enough alone). The Universal secondary filter (PN 298854) is a 10 micron filter. I had always assumed that it was a 2 micron filter since that is what I have always read the secondary should be. So unless you have a primary filter with a 2 micron element you don’t have the protection you might have thought you had. Does anyone know if Universal only specifies a 10 micron filter?

Ray Rhode
S/V Journey
E35-III, #189

 

[Loren Beach]

Our '88 M25XP has always used the stock Unversal spin-on filter on the engine bracket, and that is downstream from the Racor. Assumption is that the Universal filter (whatever size particle is being strained) has very little work to do...


As to the flow rate through the return line, I confess that I have never tried to verify the operation of the return line when under way. What with the noise of the running engine, there would be no way to hear it splash into the tank like we do when running the electric pump to purge the fuel system after replacing a filter.
I guess that the only sure way to know would be to take the return hose off the fitting at the top of the tank and see what comes out...


How did you determine that no fuel was returning?

Starting at the supply end, have your checked the supply line from the tank to the Racor to see if it is fully open and not constricted? Perhaps, unbeknowst to anyone, the engine is barely betting enough fuel to even run...
We replaced that original copper line after finding that it was nearly plugged up, like a constricted artery.

Also see reply #10 in this thread:
http://www.ericsonyachts.org/infoexchange/showthread.php?t=3585&referrerid=28

Loren

 

[Ray Rhode]

Loren,

I had just changed the fuel filters and was curious about the return flow. I was able to see inside the tank thorough the tank cleanout. It is located next to the return fitting and I could see inside and put my hand under the fitting.

Over the last couple of years I have replaced all of the fuel lines, filter assemblies, etc. The engine starts without any problems and reaches full RPM under load so I don’t think fuel starvation is a problem, but a weak fuel pump is the only thing I could think of (or would rather not think of). There is also the possibility that the Universal does not need a 2 micron filter and that is too much restriction for adequate fuel flow but I doubt it.

Ray

 

[Ray Rhode]

An update.

I checked a friends Universal M-18 yesterday and he has no return flow either. Perhaps Universal does return fuel, but then why a return line? Posted this at Torrensen and have not had any response.

Ray

 

[mherrcat]

I just replaced the fuel return line on my M18 last weekend. There was fuel in the line when I disconnected it...

 

[Loren Beach]

Return Line info

It looks like we do not have to be concerned.
I sent this thread over to my profesional diesel mechanic buddy for comment.
The gist of his reply:

"Consider no fuel flow through return a good thing unless you have a CAV Lucas type fuel primary system where there is a by pass valve system in the secondary fuel filter housing,the return line on many fuel systems is a vent line only that allows any leakage that may occur from wear to the pistons in the injection pump and the plungers in the injectors, these two areas are metal to metal seal and seepage can occur as wear takes place , the old-- old-- diesel engines in land applications use to vent the return to atmosphere and it was common to see fuel dribbling to the ground from worn systems.
Some day when we have time to discuss I will share with you details of fuel systems and why they have to be vented on the non pressure sides of the high pressure mechanisms."

And there you have it -- some more diesel trivia that I never even suspected!
:nerd:

Cheers,
Loren

 

[Ray Rhode]

Thanks Loren. I have not been able to chase down the local diesel guy and have had no responses from Torresen. Looks like I'll have to look somewhere else for trouble.

Ray