1991 P42 Fuel Filters

[Terry Cox]

Our 1991 P42 that we purchased in 2002 came equipped with a Yanmar 4JH2-TE tractor diesel and an Onan Cummins (Kubota three cylinder tractor diesel) 8KW Genset. Both have been very good performers over the years. Each engine has its own fuel filter; a spin on canister on the Yanmar and a cartridge filter on the Onan.

The PO had installed an after market unfamiliar brand fuel filter on the Yanmar and the Onan OEM was a two micron cartridge original equipment. Rather than purchase OEM spares I opted for NAPA brand spin on canisters as an alternative. Hunter installed Racor ten micron cartridge filters for both engines between the fuel tank and engine filter.

Professional transportation diesel mechanics advised me that six micron fuel filters would be more than adequate contamination protection for any diesel engine. NAPA brand fuel filter part numbers of both engines follows:

Yanmar: NAPA 3395 six micron canister filter.
Onan: NAPA 3426 six micron canister filter.
Racor: OEM 110 ten micron cartridge filter.

The Yanmar currently has 1,700 hours and Onan 450 hours.

 

[RichH]

Your professional transportation mechanic is greatly mistaken.

The universal standard by SAE for diesel equipment is a 20µM limit for particles in fuel and most manufacturers of this equipment specify a NOMINAL (arbitrary) µM rating between 15-18µM as the final filter in any filter series.

Filtration takes 'work' (consumption of energy) to accomplish. The difference of 20 vs. 6 µM when comparing the amount of 'work' required is that now the fuel lift pump will be working 3X harder as when at 20µM as a 6µM filter has ~3X the flow resistance (differential pressure drop) and 1/3 the 'flow capacity' and approx. 6X times less 'in service life' (before plugging) across that 6µM filter. That result can easily promote premature diaphragm failure of the lift pump and premature plugging of the fuel filter.
Using a smaller than specified µM can also promote the 'extrusion' of retained soft and deformable particle though such 'undersized µM' filters. Such extruded particles do not 'burn' well in the combustion chambers and will then settle out on the walls of the hot exhaust system as deposits of 'coke' - think of the primary cause of fouled and blocked water injection elbows.

Its even worse when substituting a 2µM for a 20µM --- for 10 times the increased pressure drop, 10X less 'flow capacity' and approx. 30 times less 'in service life'.
The only typical engine manufacturers that SPECIFY smaller µM retention (than the 20µM nominal limit) fuel filters is FORD, Mazda and some Volvo Engines, as those engines have 'stronger' lift pumps to be able to handle that increased load (work) due to the filtration. Yanmar engines are @ ≤20µM

In order to balance the 'work' requirements of pumps and filters when deviating from 'spec' due to the 'flow resistance' in filters (GPM/∆P) ..... for 20µM --> 6µM system, you really should now be increasing the effective surface area of those filters by 3X (filters should be 3 TIMES 'larger'). For a 2µM for 20µM substitution, that effective filtration surface area should be increased by a factor of at least 10 times. If you ignore this intrinsic requirement, consider to buy and store a CASE of filters onboard as youre going to need them due the vastly increased need for constant 'changeout' due to enhanced 'plugging' and fuel shutdown.


FWIW - that Racor 10µM is a nominal rating and therefore it will occasionally release a very small statistical probability of particles at approx. 30, 40, 50, or even 60µM. and such is well understood and accepted by the engine manufacturers. All this is based on 'statistics'.

;-)

 

[Terry Cox]

Fuel Filter

Hi RichH, perhaps, but I figure the head diesel mechanic, who has been responsible for managing a fleet of 100 pusher rigs for the past few years, knows from experience what he is talking about.

With all due respect, your reply made no sense to me, a humble sailor. Perhaps it would help if you were to simply state that a six micron fuel filter is either good or bad and whether NAPA brand is a trusted maker of these filters or not.

 

[ice breaker]

Napa is fine, and makes different micron rated filters that fit the racors. I have used them with the stock racors that Hunter provided.

Too make my life easier:

I installed a Racor 500 rated at 60 gals an hour. It is the primary for my 56hp Yanmar and a Fisher Panda 6000. I will never put more than 4gph through this filter, so the discussion about lift pressures is irrelevant. The 500 came with a 2 micron filter that I used all season, and found no issues at all with. I had a back up 30micron filter that I was ready to swap into it should there be any issues, but there were none. I plan to continue using the 2 micron. I put about 100 hr on both the panda and the yanmar this season.

Good luck.