I've got an 80-HP marine diesel engine (in a sailboat, naturally).

I've got a the Parker/Racor 75500MAX dual fuel filter system with an attached vacuum gauge to monitor resistance.

For the first few hours of operation (less than 2 hours) everything looked good: pressure was right around -3" Hg, as expected for a fuel system with 1/4" line coming from the tanks.

Sometime after this 2-hour period, the pressure started creeping up and eventually reached astronomical (-20" Hg) levels. The engine, starved for fuel started to falter.

I switched to the second filter on this system and the pressure was still astronomical. There was a slight drop, but not a drop down to -3".

My primary filters were essentially new. The bowl in the bottom was clean.

I replaced my secondary filters, bled and primed, and when the engine started up, the pressure leaped up to -10" Hg and floated up from there until the engine died again.

How can both filters show astronomical pressures like that?

Does this mean my fuel tanks are so filled with crud that little or no fuel is flowing?

Or could it be that my fuel tank vents have clogged? (Maybe a wasp's nest in a vent?)

Or is there some other explanation?

How would I diagnose this?

  • If you don't get any good responses here, have you tried the sailing anarchy gear forum?
    – Brook
    Apr 28, 2011 at 18:41

3 Answers 3


It was crud in the fuel pickup tube.

First, I switched a jerry can into the fuel line and the engine (after priming) ran perfectly.

Then, I used a priming bulb to force air back into the tank. It took several vigorous squeezes to blow the crud back into the tank from the pickup tube (and possibly the tank selector valves and the other lines.)


I have had the same problem with my boat (sail of course). Bought a fuel transfer fump and water separator/filter for the SUCTION side and recycled fuel from the inspection port to the filler, I couldn't believe the crap that filled the bowl of the filter. Took three filter changes but it is finally clear. Had to clean lines as well and now use fuel doctor additive. So far so good.


Had the same problem, engine stopping. Did all the things mentioned above. Still not solved. ended up removing fuel line, layin straight on jetty and poking thin stiff wire through. Pushed out 3 inch long compacted alge that looked like a worm. All runs well now and have installed a "do it yourself" fuel polisher.

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