Fuel Filter Fandango

Gulf Comanche · Aug 3, 2013

Hello all:
The last time I ran the boat the vacuum gauge read about 9"Hg, so today I changed all three, including the PIA Lucas CAV filter on the engine, big time mess. I bled all the air from the system and cranked her up, no problem. Vacuum reading 5.5"Hg. Then I went riding for 3 hours, back at the slip the vacuum read 10"Hg. I have one of those bulb set ups so I pumped some fuel in and the gauge goes to about 2". Crank the engine, back up to 10". Shut it down and headed for home.

Now, the CAV filter is 3 pieces: the mount on the engine, the filter, and the base, all have gaskets. When I took it apart there was a very small o-ring laying in the bottom of the base, the new filter did not come w/ one of those in the gasket package. So I figured the only place that something that small would fit was the cap screw that runs from the filter mount, through the filter, and threads into a stud on the filter base, it seemed logical.

Maybe the vacuum gauge is faulty? The tiny o-ring messed things up? I'm stumped, but the engine ran fine the whole trip, didn't miss a beat, so maybe 10"Hg is the new normal. The engine is a Perkins 4-236.

Any ideas?
Thanks
Mike

meridian · Aug 3, 2013

replace the CAV base with a spin-on adapter. That will take one part out of the
equation permanently

Gulf Comanche · Aug 3, 2013

Would love to get rid of that thing, where can I find one? Is it an easy swap out?

Forkliftt · Aug 4, 2013

Gulf Comanche said:
Hello all:
The last time I ran the boat the vacuum gauge read about 9"Hg, so today I changed all three, including the PIA Lucas CAV filter on the engine, big time mess. I bled all the air from the system and cranked her up, no problem. Vacuum reading 5.5"Hg. Then I went riding for 3 hours, back at the slip the vacuum read 10"Hg. I have one of those bulb set ups so I pumped some fuel in and the gauge goes to about 2". Crank the engine, back up to 10". Shut it down and headed for home.

Now, the CAV filter is 3 pieces: the mount on the engine, the filter, and the base, all have gaskets. When I took it apart there was a very small o-ring laying in the bottom of the base, the new filter did not come w/ one of those in the gasket package. So I figured the only place that something that small would fit was the cap screw that runs from the filter mount, through the filter, and threads into a stud on the filter base, it seemed logical.

Maybe the vacuum gauge is faulty? The tiny o-ring messed things up? I'm stumped, but the engine ran fine the whole trip, didn't miss a beat, so maybe 10"Hg is the new normal. The engine is a Perkins 4-236.

Any ideas?
Thanks
Mike

Hey Mike,
I have replaced a lot of these CAV filters and you are correct, the small oring slips onto the 1/4" bolt and fits beneath the flat washer and head of the bolt. There is a larger oring as well. It fits in a groove at the bottom of the top housing. I may be wrong, but to my thinking :nonono:

a vacuum gauge should "feel" from your Racor, and back to the tank. Trash in the valve might be the cause??

C lectric · Aug 4, 2013

For the spin on adapter try this:
Diesel CAV Filterhead Fuel Filter Adapter courtesy Marin some while back as he used them.

Your engine may simply be somewhat more tolerant of a relatively high vacuum level.
It's still not good though as the fuel pump must work harder to deliver fuel.
You could be on the verge of a starvation shutdown or power loss.

Things to check:
-tank vent clear. Sometime the hose can be pinched shut or blocked by bugs. Can be checked by opening the fuel deck fill cap when the high vacuum shows. If the vac. disappears and/or there is a hiss then the vent is blocked.
-fuel pick up tube clear. Some have a screen put over the end in the tank and the screen can become plugged. Remove the screen.
-fuel lines. can become blocked from trash sucked into them and jammed or delamination of the inner wall can cause a blockage.
-fuel filters. Some types if misassembled can cause trouble. Racors, some of them, have a check ball that can stick.

Sometimes use of a jug of clean fuel can help trouble shoot where a blockage occurs. Do not bypass the last filter though or you chance injection system damage as there could still be damaging dirt in the jug.

Gulf Comanche · Aug 4, 2013

Steve: the tiny o-ring was laying in the bottom part of the assembly like it had come loose from the capscrew threads during disassembly. I put it back on the threads and fit the filter on the engine, so the tiny ring is on the inside of the filter. The capscrew itself is hard to remove because the banjo fitting is directly above it, but there is no fuel leakage and never has been.

C lectric: thanks for ideas, will look at all of them shortly.

RT Firefly · Aug 4, 2013

Greetings,
Along similar lines...When I change the elements on the Racors, thereby removing the gauges (sit in place of the T-handles), the gauges do NOT return to "0", EITHER one! I strongly suspect they are done for. Could they simply be gummed up? They are oil filled. Opinions?
Thanks.

Gulf Comanche · Aug 4, 2013

RTF: I thought of that too, mine doesn't zero either, maybe try a new gauge?

BobH · Aug 4, 2013

On most vacuum gauges there is usually a small vent of some type to allow them to breathe ambient air. The ones I bought from McMaster have a vent that can be opened and closed. When closed the gauge will not return to zero. The gauge has to be able to breathe ambient air pressure.

Bob

Gulf Comanche · Aug 4, 2013

The gauge is the cheapest and easiest way to start figuring out the problem, a new oil filled gauge at Graingers is $22. Will make sure it has an air vent as Bob says. If that doesn't work, on to something else.

RT Firefly · Aug 4, 2013

Greetings,
Took off gauge. Lifted rubber cap on top of housing. Needle went to ZERO!!! Thanks guys.

rochepoint · Aug 4, 2013

RT Firefly said:
Greetings,
Took off gauge. Lifted rubber cap on top of housing. Needle went to ZERO!!! Thanks guys.

A quote from the Racor manual for older gauges with a small black rubber plug on top:

"Liquid filled (glycerin) gauges are recommended for high--vibration and pulsation applications (not engine mounted).
Note: Internal pressure changes may result in external fluid leakage or failure of the pointer to return to zero with the engine
off. Clean any fluid, if evident. Some models may be bled of excess internal pressure (and re--zeroed) by removing the
top rubber plug momentarily. Make sure the plug is reinstalled properly--do not push the plug into the gauge housing."

Astral Blue · Aug 4, 2013

While replacing the vacuum gauge is probably the cheapest way to eliminate the thought that the gauge might be faulty, I am inclined to think that there may be other causes to consider.

How long did it take for the reading to jump to 10?
Could you have a fuel contamination issue?
Is your sending unit inline? If so, change the location of the sending unit to somewhere between the supply line and the filters. See what reading you will get.
Temporarily lace a clear vinyl hose between the vacuum sending unit and the injector pump fuel intake port. Run your engine and observe the clear section of the hose. Look closely for air bubbles.

Vacuum gauges (even the cheap ones) have a very low incidence of failure. They are a different monster from say voltage and temperature gauges -- far more tempermental and prone to misreadings due to less than ideal conditions, but not likely to fail unless exposed to adverse conditions (like any instrument).

Gulf Comanche · Aug 14, 2013

OK, I bought a new gauge at Grainger's and installed it last weekend. Ran the boat for a couple hours, 3.5"Hg was highest reading. As for the old gauge, not sure if it was the problem or not; pulled the little rubber plug out of the top and it went to zero. This gauge was always a bit hard to read because it had both pressure and vacuum readings on the dial. It was also 4 years old, probably not broken but the new one has vacuum readings only and is much easier to read. So, problem appears solved for now, we'll see for sure after a couple more runs.
Thanks to you all for the help. Steve (Forkliftt), thanks for the phone call.
Mike

Fuel Filter Fandango

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meridian

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C lectric

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