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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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  #1  
Old 11-26-2010
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Clogged Primary fuel filter.

My number 1 primary filter clogged the other day. I removed it and expected to see some hideous growth or something on the filter. Was surprised that it didn't look too bad (see picture). It looks worse (darker) in the picture than it actually does. My questions are: How bad does the filter look to someone who knows what they are doing? Is that algae or just dirt in the filter? I've also included a picture of the filter bowl (which I haven't drained yet, it's tough to get to). I think (hope)the darkness below the filter is simply a lack of camera flash reflection. Filter bowl #2 which is functioning fine looks about the same.

I put in a 6 gal. tank to avoid fuel problems. On the other hand, my maintenance log says the filters have been in there two years! I honestly thought it's been about 6 months! Thats probably when I checked them). Looks like I've been a bad boat owner. Glad I have a bank of filters!

Symptoms (in case anyone is interested): The motor (Yanmar 2GM20) was purring along at 3000 RPM, then I heard the RPM's dip very quickly. The motor resumed normal operation, and I pretended I didn't hear what I heard. About 1/2 hour later, the RPM's dropped radically to a very erratic 900, and the motor acted like I had air in the lines (which I have experienced). Switched to #2 primary filter and off we went. I now realize it sounded like air in the line because the motor was starving for fuel, just like when air is in the line! (duh! )
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Clogged Primary fuel filter.-014.jpg   Clogged Primary fuel filter.-1-filter.jpg  

Last edited by L124C; 11-27-2010 at 12:03 AM.
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Old 11-27-2010
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The pic of the pleated filter suggests that this filter had a LARGE 'block' of air as indicated by the lighter color on the upward portion of the pleats. This 'air block' (if it actually happened) radically decreases the 'effective surface area' of the filter and causes 'higher velocity' through the filter which in turn consumes a LOT of energy due to the now higher 'differential pressure' through the filter and in turn cause the filter to 'choke', etc.

Simple speak- looks like an 'air lock' on the upstream side of the filter. Therefore check all the fittings, gaskets, etc. immediately 'upstream' of this filter. This filter should sent to a filter lab and determine the residual flow capacity vs. differential pressure and then if blocked then analyse for the 'nature of the contaminent'. Since this is a 'primary' filter it 'should' be approx. 30µM ... which usually have a LOT of 'flow capacity' and low differential pressure, etc. Lab testing is quite expensive.

It would be best if you could describe (sketch if you can) the ENTIRE fuel delivery system, including the 'visual' condition of the filter immediately 'downstream' of this one. List ALL the µM rating in sequence from the tank to the engine 'guard' filter, etc.

That 'black crap' in the sump of the filter bowl is probably a fungus (resin forming fungus) as its exceedingly rare that is such an 'algae'. That the 'crap' is stratified in the bottom of the bowl and there is no 'black slime' on the filter, I would suggest that 'fouling' is NOT the 'problem'.

;-)

Last edited by RichH; 11-27-2010 at 12:05 AM.
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Old 11-27-2010
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L124C, the filter is dirty and ready for replacement but it doesn't look clogged. I'm with Rich in thinking you probably have air in the line.

That definitely looks like sludge in the bottom of the separator though. If it is sludge the tank should be cleaned.
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Old 11-27-2010
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Thanks for the replies! So, if I understand correctly, the "clean" section of the filter may indicate where an air pocket was in the separator. And this pocket existed while the motor operated for an extended period?
A 6 gal tank and a hose with a barb fitting are all that is upstream from the filter. I learned the hard way how full I had to keep the tank when I first installed it, while motor sailing at 11PM! I always thought the tank connections provided by Vetus were sub standard. However, I was under the impression that if you had any air in the line, the motor wouldn't function much longer, much less a "pocket" of air (with the exception of at least one model of Yanmar motor I know of) . Apparently that is not correct?
It will be interesting to see if that actually is sludge. I put the small tank in to keep the fuel fresh. I buy fuel from truck stops, thinking they have a lot more diesel turn over than a regular gas station. And, I've been using "Startron" for 6 years because the PO's did. It always sounded like snake oil to me, but I thought "well if it worked for them" (with a 20 gal) tank)..... According to Startron, the enzymes magically digest almost anything. Anyway, am I understanding the situation with the air pocket correctly?

Last edited by L124C; 11-27-2010 at 11:44 AM.
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Old 11-27-2010
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The engine won't run if the air makes it to the injection pump but it could manifest as you described if one of the filters is air locked and only allowing limited fuel flow. It is a reach but possible. In any event I don't think the primary filter is plugged. How did the secondary filter look? Secondary filters are much finer and will clog more easily.
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Old 11-27-2010
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A (rare) 'air block' will/may cause extremely high 'differential pressure' across a filter and if the differential pressure exceeds the flow rate capability (per filter surface area in contact with the 'upstream' oil) the actual flow getting through the filter may be 'less' than required by the engine. Such a situation would allow the engine to be run at 'low' rpm but not high rpm.

How many filters in the 'filter train'? What are their µM 'rating', what does the surface of the filters downstream of this one look like?
If you have gages on these filters what are the values at 'cruising rpm', etc.?

Last edited by RichH; 11-27-2010 at 12:58 PM.
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Old 11-28-2010
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Fuels clean!

Drained the separator bowls. Fuel is crystal clear in both. Good news, I would have been really disappointed if it wasn't (sorry Startron!). Next stop....Secondary filter.
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Old 11-28-2010
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With crystal clear fuel in both sumps, Its highly doubtful that debris clogging is the cause of your problem. I'd suggest looking for obstruction and/or an 'air leak' in the lines all the way from the 'engine side' of the primary filter all the way to the end of the dip tube in the tank.

Id investigate for 'crud' blocking the 'entrance' to the dip tube - and if there is a 'mesh'/screen in the inlet to the dip tube, I'd totally remove it. Id also carefully assay all the (probable) compression fittings for cracks, pipe dope or 'tape' applied to these fittings in this tubing zone. Compression fittings are notorious 'leakers' in vacuum service ... and should be assembled 'dry', not with 'dope' nor 'tape'. I'd also examine how 'tight' the brass ferrule portion of the compression fitting fits on the copper tube, if loose you will have to 'trim back' the copper to where the copper isnt 'compressed' - if the geometry of the tubing run allows it.
Lastly, Id replace the sealing gaskets on the Racor housings as they are 'flat gasket' configuration and are prone to air leakage when under high vacuum if the sealing surfaces are not 'perfectly flat' or if there is and 'crud'/dirt on the sealing surfaces. These gasket MUST be clean and must be wetted/wiped with fuel oil each and every time the housing is opened - to help affect a seal.

Also, I suggest you get some gages installed on these filters .... so you can monitor WHEN to change, and if and where there is an obstruction or air leak, etc.

;-)
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Old 11-28-2010
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RichH,

Would you please say more about installing gauges on filters.
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Old 11-29-2010
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L124C

Is your tank vented?
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