Bleeding the fuel system-I dont believe it!

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ffiill

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I finally got around to reinstalling my fuel pipework from my twin tanks either side of the engine.
Everything was piped up and taps turned on and everything seemed leak free.
I unscrewed the bleed screw on top of the CAV filter-nothing!
This was how it was when after cleaning the CAV filter a year ago I found diesel bug which I assumed was blocking the piping.
I checked the bottom of tank exit fuel lines by loosening a union-fuel.
I then realise that the 10 gallons I had put in(two 40 gallon tanks)was not enough to fill the tanks to the level of the top of the CAV filter!
The system is tank to CAV filter to lift pump to onboard engine filter to injector pump.
Having just added an emergency 2 gallon tank which sits above one of the tanks I can fill the filter from above with enough fuel to allow me to operate the manual primer on the pump.
Without this I guess I could have messed about priming the filter through the bleed screw hole! and then used the lift pump primer.
All Mercedes recommended for the fuel system for the OM636 was a simple gauze inline pump between the lift pump and tank with the heavy duty cleanable engine filter doing the fine filtering.
 
Dinghy pumps are marvellous things for slightly and temporarily pressurising tanks. For example, if my tanks are getting low, I can transfer all my fuel from one tank to the other with the dinghy pump. It only needs a bit of rag to temporarily plug the approriate air vent. I'm sure you could do similar to prime your filter.
 
ffiill said:
All Mercedes recommended for the fuel system for the OM636 was a simple gauze inline pump between the lift pump and tank with the heavy duty cleanable engine filter doing the fine filtering.
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Probably because the lift pump is not a finely machined high pressure precision variable volume pump, the injector pump on the other hand.....
If it can fit though a gauze, it wont damage the lift pump.
 
How practicable would it be to move the lift pump so it's below the fuel tanks and before the primary filter? That way, it's self priming as long as there's fuel in the tanks and a tiny leak at the filter will put a bit of fuel in the bilge, rather than drawing air into the system, stopping the engine just when you'd really prefer it kept going.
 
When I change my filters I suck the diesel through with a pela extraction pump to the engine filter, a few pumps and the system is full with no air bubbles.
I have a self sealing blead nipple on my engine filters in place of the original bleed screws, it was made for easy brake bleeding and they come in different threads, makes it an absolute doddle.
 
PaulR said:
about to do this one ours - have you put the bulb primer pump before or after the glass bowl filter unit?
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My one is between the 2 filters because the hose was longer there & there was room to fit it. The first filter did not fill on its own without some form of priming. With the bulb, both fill easily.
I would add that my first filter is mounted on studs with butterfy nuts so it can be removed easily. When it needs changing, I disconnect the fuel line from the tank, Release the filter & the hose between the 2 filters is long enough for me to swing the filter over a bucket to drain it & change the element.
This is far easier than trying to do it in a restricted position & trying to catch fuel in a bottle which is difficult. It also makes it easier to get the sealing rings seated properly first time.
So when you fit the bulb primer, consider putting a longer piece of hose in to allow you to do that if it helps
 
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The lift pump on my MD22 can take a long time to pump the fuel to the filter , last time I kept the stop out and turned the engine a few times then finished with the lift pump , I expected by doing this I would had to bleed each injectors but it worked with touching the injectors .
It may had just been luck but I plain to do the same next time .
 
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