Irrational fear of losing fuel pressure

indigoE

New member
2003 passenger van, 160,000 miles

A while back, we had our fuel filter replaced by a local (independent) garage which works on mostly Mercedes. Drove from the East coast to New Mexico, no problems. The "water in fuel filter" light came on, and (as I have done many times) loosened the knurled knob at the base of the filter holder. What I did not know is that the filter had been improperly placed in its collar-bracket so that the knob could not re-seat securely, so when we drove it, fuel pressure was lost.

Loosened the bracket, rotated the filter, tightened the knob, and (having read that the mechanical fuel pump can re-prime the fuel line, if cranked for several minutes) cranked the engine for a long time, but I could see that air in the plastic line did not budge. Had to have it towed to a garage, where they re-primed it in no time. Unfortunately, I was in the office when they did this, so missed their technique).

So after that long-winded saga, I ask: What are the necessary steps to re-prime (with the mechanical fuel pump)?? Is there any equipment which would facilitate the process?
 

lindenengineering

Well-known member
Normally speaking simply filling the fuel filter with fuel should do trick!--BUT--
If the system is empty or there are huge voids present then pressurizing the tank and feeding system with shop air will do the trick.

We have a tool that supplies low shop air pressure via a big rubber cone adapter to the fuel filler neck.
This not only aids filling the low pressure pump but assists in getting fuel to the HP pump where you can then get some high pressure fuel flow going.

We also use the tool and methodology to check previous DIY filter repair/replacement and customer's who supply their own filter for us to fit.
Hope that helps.
Dennis
Mechanic
 

hkpierce

'02 140 Hi BlueBlk Pass
If you don't have a shop handy with a cone and low pressure air to back feed through the tank's fill tube, you can also get a long way there by using a length fuel hose and feed diesel into the tank side of the filter and opening the bleed screw on the top of the filter. If necessary, back feed the fuel line from the tank also.

But I would guess that you have other problems. My guess is that you still have air coming into the filter from somewhere as a result of either damage to the water relief value by the mechanic when he removed the old filter from the cage-type bracket and not knowing of the presence of the valve; AND/or a new air leak from the water sensor, fuel lines AND/or return valve as the result of your efforts.

By the way - I have NEVER found water in my filters and now simply disconnect the sensor due to many false signals - others on this forum strongly disagree. :2cents:
 

indigoE

New member
Have noticed several Sprinter owners report that the "water in filter" warning is often (or always) false. One post mentioned a European fuel filter which does not have a water sensor and no drain valve... which eliminates one possible air leak. How important is the drain valve?
 
Last edited:

krisinak

New member
this thread got me thinking. how much water is a water dispersing fuel additive capable of "soaking up"? maybe in terms of ML/L. i use optilube and never have seen my water-in-fuel annunciation.
 

autostaretx

Erratic Member
this thread got me thinking. how much water is a water dispersing fuel additive capable of "soaking up"? maybe in terms of ML/L. i use optilube and never have seen my water-in-fuel annunciation.
The usual quoted capacity is "equal amount of water"

So if you pour in a pint of the drying fluid, it can handle up to a pint of water.

I suspect they are primarily acetone (a common laboratory drying agent), and one-to-one is the usual expectation there, too.

Typical examples:
http://www.acehardware.com/product/index.jsp?productId=1452148&KPID=1253834
and
https://www.franklinoutdoors.com/ProductDetails.asp?ProductCode=79-MDR559
(one of which even gives the capacity)

--dick
 

SneakyAnarchistVanCamper

Reading till my eyesbleed
this thread got me thinking. how much water is a water dispersing fuel additive capable of "soaking up"? maybe in terms of ML/L. i use optilube and never have seen my water-in-fuel annunciation.
I was taught in fuels class to NEVER use water dispersing fuel additives. Water is the #1 cause of seized injectors, dissolved in additives or not. Ultra small clearances between the needle and its bore must have fuel to lubricate it; water displaces this film, leading to metal to metal contact.

The proper method is to drain/siphon the tank out.



If you want to solve this fear, which I think is well founded, you could install an inline pump to push from the tank instead of suck, and replace the filter with an aftermarket part that doesn't have the supposedly failure prone wif drain. Might want an aftermarket de-waterer/sedimenter too, I wouldn't feel good running without one. Or you could just replace the filter assembly with brand new parts and be very gentle with it and only drain it if the light is on.

https://sprinter-source.com/forum/showthread.php?t=53045
 
Last edited:

indigoE

New member
i have been searching the forum for the definitive procedure for purging air from 2002-2003 fuel lines (after changing the fuel filter, or due to surprise air leaks). Adding an in-line electric pump seems a bit extreme, if it's safe to assume that MB engineered the OM 612 properly....

1. Seems that filling the fuel filter is always recommended (requires having a kit, ready in the van for roadside situations: bottle with fuel line, diesel fuel, replacement o-ring...)

2. One post mentioned opening the water drain prior to cranking the engine to allow air to escape. I did not do this... could explain why I was not able to purge air from the lines.
 

misterbond10

New member
you should never ever crank the motor for several minutes. thats not good for the engine and most certainly the starter. Pretty much any vehicle says to never crank the starter for more than a minute without letting it cool down afterward for 30 minutes or so

turning the ignition to the ON position will pump fuel for a few seconds without turning the starter
 

indigoE

New member
turning the ignition to the ON position will pump fuel for a few seconds without turning the starter[/QUOTE]

Unfortunately, the 2002-2003 Sprinters are unique in that they have mechanical fuel pumps, so prolonged cranking is unavoidable. No question that purging air from the lines more challenging on those Sprinters. I have been looking through older posts to establish what steps are recommended to minimize cranking (and my personal experience showed that extended cranking does not necessarily purge air from the lines). I made note of the posts above which suggested 1.an after-market electric pump, or 2. pressurizing the fuel tank (could this be done on the roadside with a modified filler cap fitted with a Schrader valve?).
 
Last edited:
I've had good success siphoning the fuel supply line with a 3/8 clear plastic hose. When fuel starts to show, quickly attach to filter. You carry can this hose with you at all times in case of breakdown.
 

Aqua Puttana

Poly - Thread Finder
I've had good success siphoning the fuel supply line with a 3/8 clear plastic hose. When fuel starts to show, quickly attach to filter. You carry can this hose with you at all times in case of breakdown.
Will a marine/boat primer bulb connected to the OM612 WIF drain tube work to prime the system without disassembly?

One example.

FuelBulb.jpg

https://www.amazon.com/Assembly-Out...coding=UTF8&psc=1&refRID=2SECPTA47A5D0JKQQ0CB

Also available for 5/16" and 3/8" hose size.

vic
 
Last edited:

Top Bottom