What % of diesel returns to the tank?

[Beneteau381]

Old thread but I have no fuel return to tank.

The return line goes into the top of the last filter on the engine. Engine never misses a beat and when I have had to bleed the engine post filter change, it bleeds air very fast with minimum cranking. This system was an upgrade when all the fuel lines from the tank were replaced and new filter unit installed. The fitter decommissioned the old fuel return lines to the tank. Upgrade was 12 years ago.

I know some people do this but the return helps to cool the injectors, doing this ensures warm fuel is recycled through the filter and head instead of going back to the tank to dissipate heat

 

[Bilgediver]

I know some people do this but the return helps to cool the injectors, doing this ensures warm fuel is recycled through the filter and head instead of going back to the tank to dissipate heat

This circulation on the older systems is almost nil as it is only the spill leakage from the lapped needle to body clearances that is lost. and its main purpose is lubrication of the injector needles. On many older small Volvo marine diesels it was common practice to feed this spillage back into the fuel system somewhere between the the filter and injector pump. One downside was that if there was an air leak at a filter housing then this air might also recirculate. The is also spill leakage from the fuel pump plungers and this on many engines finishes up in the sump, the amount depending on age and internal wear of the pumps.

 

[AntarcticPilot]

This circulation on the older systems is almost nil as it is only the spill leakage from the lapped needle to body clearances that is lost. and its main purpose is lubrication of the injector needles. On many older small Volvo marine diesels it was common practice to feed this spillage back into the fuel system somewhere between the the filter and injector pump. One downside was that if there was an air leak at a filter housing then this air might also recirculate. The is also spill leakage from the fuel pump plungers and this on many engines finishes up in the sump, the amount depending on age and internal wear of the pumps.

Depends on what you regard as "older"! My VP2003 (1989 vintage) returns far more fuel to the tank than is burnt, and after long running, the tank becomes noticeably warmer.

 

[Beneteau381]

This circulation on the older systems is almost nil as it is only the spill leakage from the lapped needle to body clearances that is lost. and its main purpose is lubrication of the injector needles. On many older small Volvo marine diesels it was common practice to feed this spillage back into the fuel system somewhere between the the filter and injector pump. One downside was that if there was an air leak at a filter housing then this air might also recirculate. The is also spill leakage from the fuel pump plungers and this on many engines finishes up in the sump, the amount depending on age and internal wear of the pumps.

The is also spill leakage from the fuel pump plungers and this on many engines finishes up in the sump, the amount depending on age and internal wear of the pumps.
Really? never heard or seen that one in all my 60 years of fixing diesel donks

 

[Bilgediver]

The is also spill leakage from the fuel pump plungers and this on many engines finishes up in the sump, the amount depending on age and internal wear of the pumps.
Really? never heard or seen that one in all my 60 years of fixing diesel donks

This is the case with most smaller Volvo, Yanmar and even Beta thought the Beta have possibly not reached the age where is is a problem. This is one reason for the recommended annual change of sump oil. There is a minute leakage of diesel from each pump plunger which increases as the years go by it is a similar leakage to that in the nozzles which is fed back to the fuel tank or recirculated.

It is not a problem so long as the correct oil change schedules are maintained. However in extreme cases has caused engine runaway. I have seen this on one occasion however the engine was stopped before damage was done.

It is possible to detect the smell of diesel on the sump dip stick of engines where the leakage is excessive .

 

[vyv_cox]

The is also spill leakage from the fuel pump plungers and this on many engines finishes up in the sump, the amount depending on age and internal wear of the pumps.
Really? never heard or seen that one in all my 60 years of fixing diesel donks

The only return on my Yanmar 3GM30F is from the injectors. I measured it a few years ago, a very small figure, 1 or 2 ml per minute at cruising revs. I have never smelt diesel in my sump oil.

 

[Beneteau381]

The only return on my Yanmar 3GM30F is from the injectors. I measured it a few years ago, a very small figure, 1 or 2 ml per minute at cruising revs. I have never smelt diesel in my sump oil.

I can hear the return dribbling in to my tank, so quite a bit, the one I was replying to, diesel from the pump plungers in the sump? nah.
Stu