I have a quick question. I recently retired an '84 300D that had the screw-type primer on the lift pump. The '82 240D that I replaced it with has the straight primer pump.

I really liked the screw-type style, which seemed to act also as a bleeder. It seems that this other style pushes air back to the fuel tank to bleed. Is this true?

NO, its not true

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Yes it is true. The air goes to the canister filter at the three-point connection, to the cigar hose and returns to the tank.

Don't belive it? Change your fuel filter without filling it with anything. Tighten it, then hit the primer 30 times. No cracking of anything required. Where did the air go? No big mystery.

It might be more obvious if you could see through your clear fuel lines and watch the bubbles.

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1982 300CD Petrol/Black Leather

If I did that, my car wouldn't start.


Still - both new/old pumps work the same....and a leaky old-style pumps means it needs to be replaced, not that it's bleeding air as designed

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1981 240d - 135k - Arlene

Huh, I had always thought it was the air escaping the system that could be herd, learn something everyday

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Changing speeds a bit...

I know with some pumps, you must have enough head for them to work properly (or properly, you shouldn't be trying to raise the fluid higher than the pump's capacity). So...

If there was a column of air between the fuel tank and the engine (i.e. when you change fuel lines), would the amount of fuel in the tank make it impossible to purge the air?

I have this friend (totally hypothetical, of course) who has about 1/4 tank of diesel, has gone through the charge of two batteries and about 1000 primer strokes, and still has a car in his driveway that doesn't start. Do I... I mean.. does this guy need to get more fuel in his tank or is it likely something else?

hypothetical speaking, of course.....when my friend ran into this problem.....he cracked his injector lines and cranked patiently (waiting b/w cranks) but loooong cranks. My friends car started soon after this

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1981 240d - 135k - Arlene

Likely something else. The engine should be running in that amount of time even if you started with a completely dry injection system and only fuel in the tank.

Any insights on how it does work? I always assumed that the screw-type released the air at the handle (based on the fact that it begins to spill diesel once the air has passed).

I am confused by where the air goes with this type primer. When I pump it I see air bubbling at the engine side of my in-line fuel filter. I'm trying to get the air out of the system or find the leak that is keeping my car from running.

[QUOTE=vjw;1827290] (based on the fact that it begins to spill diesel once the air has passed).

The problem with the older style is they do spill fuel (leak) when they need replacing, they shouldn't do that.

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

When you pump your primer pump the air exits a small hole on the primary (big) fuel filter housing, not sure where, doesn't matter, but you will hear a difference in the sound when your pumping. You can still get the old "screw down" type but I would stick with the new "black handle" one, more better

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

THanks Stevo

The black one is considered an upgrade to the older screw down type.

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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There is only going to be a "hole" in the filter housing if you make one by loosening a hose or fitting. The return line hollow bolt works well. The sound that you hear is most likely the relief valve on the injection pump. It just relieves excess pressure by diverting fuel (or air) into the return line.

As counterintuitive as it may seem, the large filter is the secondary filter. The inline filter upstream from the fuel pump is the primary.

I did that earlier today. Don't tell me our cars are different?

Here's a question for you: Have you tried it?