Debunking myths... Fuel filters, do you really need to change them?

[DogWatch]

Not just boats here, but has a fuel filter that is not clogged with fuel bug ever fixed an engine that is dead to the world.

I have always serviced my own cars, boat engines etc. and I rarely change fuel filters on spec. Nor in my experience ever had a fault caused by a fuel filter. Now don't get me wrong, if I lived in a desert with sand storms and the like I would change them religiously, but here in the UK our fuel tends to be clean and if you look after the tank, well..

People often come on here with stuff like my eber wont start and within 2 posts they will be told to change the fuel filter. These people never seem to come back and tell us yes that fixed it thanks, it is often more serious.

When I have changed fuel filters the old one always looks brand new coming out. What is the point!?

Also please do not confuse this with draining the water trap, I am referring specifically to the filter element.

 

[tdw]

Not just boats here, but has a fuel filter that is not clogged with fuel bug ever fixed an engine that is dead to the world.

I have always serviced my own cars, boat engines etc. and I rarely change fuel filters on spec. Nor in my experience ever had a fault caused by a fuel filter. Now don't get me wrong, if I lived in a desert with sand storms and the like I would change them religiously, but here in the UK our fuel tends to be clean and if you look after the tank, well..

People often come on here with stuff like my eber wont start and within 2 posts they will be told to change the fuel filter. These people never seem to come back and tell us yes that fixed it thanks, it is often more serious.

When I have changed fuel filters the old one always looks brand new coming out. What is the point!?

Also please do not confuse this with draining the water trap, I am referring specifically to the filter element.

The way I figure it , the filter element is an inexpensive thing so why not change it every service, which is our case is once a year.

 

[RobHom]

Not to be argumentative, but here in Florida...I drive a 2004 Diesel pickup truck and I have to change the fuel filter on schedule or prior to the 16,000 mile limit as it will be very dirty and begin constricting the flow of fuel.

Where boats are concerned here in FL...the changing of fuel filters is generally done as required...though I tend to stretch it out. We have far more trouble with condensation in the tanks if they are not full...and thus we can have more problems with bugs and growth in the fuel itself....

And yes... I am referring to the "fuel filter"..... On gasoline engines and vehicles, I had to change the fuel filters far less frequently.

 

[Bilgediver]

Not just boats here, but has a fuel filter that is not clogged with fuel bug ever fixed an engine that is dead to the world.

I have always serviced my own cars, boat engines etc. and I rarely change fuel filters on spec. Nor in my experience ever had a fault caused by a fuel filter. Now don't get me wrong, if I lived in a desert with sand storms and the like I would change them religiously, but here in the UK our fuel tends to be clean and if you look after the tank, well..

People often come on here with stuff like my eber wont start and within 2 posts they will be told to change the fuel filter. These people never seem to come back and tell us yes that fixed it thanks, it is often more serious.

When I have changed fuel filters the old one always looks brand new coming out. What is the point!?

Also please do not confuse this with draining the water trap, I am referring specifically to the filter element.

I think it is worth changing filters regularly if only to see wha the filter is catching and give warning when the bug has arrived on board

 

[prv]

I don't think I have a bug infestation (brand new tank) but there was lots of gunge in the filter last time I changed it. Depends where you buy your fuel, I guess.

Pete

 

[duncanmack]

Oddly enough, this subject came up earlier in conversation, and I had to look up fuel spec to answer a question.

EN590 for diesel fuels ( the most recent standard I could lay my hands on)
Water content 200 mg/kg. Sulphur content 50mg/kg (ULSD). Other contaminants 24mg/kg. FAME (Bio) content up to 5% of which the water content can be up to 500mg/kg. Sulphur content 10mg/kg, Other contaminants
10 mg/kg. Glycerin up to 0.25% by weight.

So, say you use 100 kg of good clean diesel - 117 litres say - you might expect your filters to trap about 1 gramme of various contaminants, 12.5 grammes of glycerin and about half the water present in the fuel (the other half should precipitate out and be caught in the water traps in the system) - about 18 grammes from the diesel plus about 5 grammes from the Bio, totalling 23. Grand total of "****" is therefore 36.5grammes. Not a lot really, BUT this is the stuff fresh out of the refinery.

Marina diesel is almost certainly much dirtier than this - for a start it's red, it's kept in a very damp, humid tank and the turnover of the fuel is not nearly as rapid as in a filling-station forecourt. So you would expect something worse than this - especially as the stuff is kept in less than ideal conditions on the boat.

All very well.

I can, however, from my experience in the garage, say that I've cut open fuel filters which have done 10000 miles and they've been filthy, and other which have done 3 times that and they've not been too bad.

Not so many years ago the vehicle manufacturers recommended that after 100k miles the fuel tank was removed and "purged". I did this on my first diesel car and got about 1 litre of absolute **** out of it after the dregs were allowed to settle. I was horrified, but it actually equated with the spec for the fuel at the time. The VMs don't recommend this any more BTW.

We frequently come across vehicles which have filters that are seriously limiting the amount of fuel being delivered to the pump. Some have had the filters changed religiously others not.

Conclusion? Yer pays yer money......

 

[William_H]

Fuel filters

I would suggest that the whole question is a variable quantity. The need to change a filter after a specific time can vary possibly by a 100 fold amount. It all depends on your tank condition and that of your suppliers.
Perhaps the best bet is to have switchable alternative filters or a handy replacement filter and run the filter until either it is clearly clogged or you lose your nerve and replace it anyway.
If this were an aircraft part or indeed part of any fleet you would start using a conservative replacement period then on the basis of filters removed and inspected you would vary the period up or down. Continually adjusting the period on the basis of removed filter condition.
But even this approach depends on continuity of fuel supplier conditions and tank conditions.
So in the end for a single operator it is not surprising that people replace at a very conservative period arguing that cost is small compared to the inconvenience of engine failure. So no answer at all really, olewill

 

[charles_reed]

I've 2 filters and a settling chamber in my system - the 1st, coarse, filter will take x7 the actual fuel throughput so I just watch it (and haven't needed to change it in 4 years) - the fine filter on the engine (much smaller than the coarse) I change annually and twice it has had visible contaminants.
80% of my fuel (in Europe no red diesel for yachties) comes from roadside filling stations and goes in through a filter-funnel.

 

[omega2]

We change ours when the engine stops, and then only the prefilter, caused by idleness in not draining the bowl. All old fashioned CAV units.

 

[PetiteFleur]

I have religiously changed both the primary & engine yearly and each year I've split open each filter to see wether contaminated or not - but 3 years ago I didn't for various reasons and the engine was fine all season BUT when changed at layup the primary filter(CAV 296) had visible gunge on the top of the filter but clean internally. Since then I've changed yearly.
I also keep spare filters on board if I need them during the season.

 

[Twister_Ken]

We change ours when the engine stops, and then only the prefilter, caused by idleness in not draining the bowl. All old fashioned CAV units.

Sounds a bit labour intensive. My engine stops every time the sails go up.

Or if you mean every time your engine ceases to run when you want it to, how quickly can you change the filter when being wooshed through, let's say, Poole entrance channel.

 

[rickym]

Used not to bother and just empty the bowl, change filter every 2-3 years no excuse as it was really easy to get to, then... sailing in a serious gale shook up all the crud in the tank and blocked the fuel line and filter, had to claw off a lee shore and sail to our destination, late arrival and anchored outside. no real drama, however SWMBO was not impressed! Never confessed to the 'no change' regime just said it was one of those things, all part of sailing! Took her 2 days to recover to move off again.

I now change it religiously every year even write the date of the change on the filter, will probably never have a problem again but for peace of mind and a happy SWMBO.....

 

[Modulation]

I tend to agree with you based on my own experiences. I change the fuel filter to my Yanmar 2g every 2 - 3 years - its always as clean as a whistle, What I HAVE found though is that the air filters breakdown much more quickly. What tends to happes is that the foam spongy stuff goes hard and constricts the airflow causing the engine to lose revs. This happened first a few years back gouing up the Thames to St Kaths - not a place to be without power. Tooks us a while to diagnose the cause as the air filter looked completely ok. Since then it'd new airfilters every year.

 

[Spyro]

I think we are a bit over cautious about changing filters on our boats. I clock up around 20,000 miles a year on my diesel van I reckon on an average 30mph so looking at 600-700 hours a year. Nothing like what most of us do in our boats. I know the arguments about dirtier fuel and worse conditions but every time I've changed my secondry filter which sometimes has done 3 seasons it looks like new. I still do the primary every year but I'm sure there's no need.

 

[Pye_End]

People often come on here with stuff like my eber wont start and within 2 posts they will be told to change the fuel filter. These people never seem to come back and tell us yes that fixed it thanks, it is often more serious.

My eber stopped, and it turned out to be a partly blocked filter. Took a sample from the bottom of the tank and indeed it was a rather cruddy, and the stuff in the separator wasn't great either.

Engine filter thus also on this winter's list.

 

[Latestarter1]

Not just boats here, but has a fuel filter that is not clogged with fuel bug ever fixed an engine that is dead to the world.

I have always serviced my own cars, boat engines etc. and I rarely change fuel filters on spec. Nor in my experience ever had a fault caused by a fuel filter. Now don't get me wrong, if I lived in a desert with sand storms and the like I would change them religiously, but here in the UK our fuel tends to be clean and if you look after the tank, well..

People often come on here with stuff like my eber wont start and within 2 posts they will be told to change the fuel filter. These people never seem to come back and tell us yes that fixed it thanks, it is often more serious.

When I have changed fuel filters the old one always looks brand new coming out. What is the point!?

Also please do not confuse this with draining the water trap, I am referring specifically to the filter element.

Not sure if this post is tongue in cheek………….

I have been involved with a lot of older boats that have gone from "slow to fast" when repowered; I've learned that lots of **** can get dislodged from the fuel tank bottoms and walls requiring filtration in "steps." In other words, filtering from, let's say, a nominal 30-50 microns (a very fine strainer) to a nominal 10 microns, to the nominal 2-5 micron typical on engine "last chance" filter. In a new boat with clean tanks most anything will get you by until a fuel provider pumps some unwanted **** or into your tank. By the way I refuse to include 50 year old CAV fuel filters in any discussion, time passed them by long ago and they are as much use as a rubber eye. None of this is to do with the fuel bug, just protecting end ensuring fuel pump and injector durability.

As an option to your fuel system, a fuel vacuum gauge will pay for itself quickly when understood by the boat operator. Fuel pressure drop across a filter is a function of fuel flow vs. restriction, and a well designed fuel filter system, which includes all the types of fittings and "stuff" incorporated into the finished system, should start out CLEAN less than 3" of Hg restriction. My work over the past 40+ years has shown that "most" diesels with properly operating lift pumps and fuel systems can tolerate about 10" of mercury (Hg) restriction before starving for fuel. Always put your vacuum gauge after your "off engine" fuel filters, but before any pumps.

The "micron rating" of fuel filters is a very simple way of allowing someone to select one of the requirements for filtration. From general experience with fuel systems involving the common engines discussed in these forums, I've learned that a nominal micron rating is not necessarily the best way of choosing correct filtration. Micron rating should only be used to categorise the media since the ratings were developed based on single-pass efficiency tests using uniform spherical particles as a system contaminant. In real life, diesel fuel contains contaminants of various sizes ranging from sub-micron to 100's of microns in size.. For a perspective on the size of a micron, 25 microns = .001" or 50 microns is about the diameter of a human hair.. Tobacco smoke particles run from about .01 to 1 micron in size. Visual inspection of a used filter does not take you very far when dealing with stuff this size!

Many filter, engine, and hydraulic equipment companies do not recognise micron ratings as significant and specifically recommend the use of "Beta ratio" in selecting a filter to meet system requirements. Beta ratio (multi-pass test method) ANSI/B93.31-1973, ISO 4572-1981; this is the only test accepted by ANSI, ISO and NFPA. It is the industry standard for measurement of efficiency.

The Beta ratio is determined by counting the number of particles over a given size upstream of the filter and dividing that number by the number of particles over the given size downstream of the filter. Simply put, a nominal 2 micron filter may only capture 94% of 2 micron particles, 98% of particles 10 microns, and close to 100% of particles above 10 microns.
Caterpillar specification filter (one of their most modern "last chance" filters on a very expensive engine (about £80,000.) - CAT P/N 1R-0749) have these ratings: 100 GPH maximum flow, with Beta ratings as follows: 2 microns at 96.5%, 3 microns at 97.8% and 10 microns at 99%. I honestly believe that a company like Caterpillar would only use the best filtration technology available to protect their engines, and I would like to see Racor subscribe to a much more widely accepted filtration rating for their filters and not just use name recognition for their marketing hype. I'm not a big Racor fan.

What I do have in the bank is hard evidence that boaters with a good filter set up and maintenance regime NEVER squawk about pump or injector problems.

 

[NUTMEG]

Quote: By the way I refuse to include 50 year old CAV fuel filters in any discussion, time passed them by long ago and they are as much use as a rubber eye.

Sorry but can you explain this please ,'thanks

 

[TrueBlue]

As with all things, it pays to keep an eye on what's happening and adjust one's regime accordingly (a bit pompous)

I've had three occurrences of a blocked primary fuel filter - all happened at inconvenient times - when motoring along; engine splutters and stops suddenly.
I've also had to recondition my injector set twice.

So now I change the primary filter twice a year "regardless" and dose my fuel with "Magico snake oil bug eradicator" at every fill.

They may not actually do anything, but I think they do and haven't had a blockage or free water since.

Doesn't cost a lot AND it buys me peace of mind.

BTW - my Eber (well, Mikuni) filter was the original and "well black", so after 10 years I changed it. Amazing , now it doesn't hunt.

So there, you can't convince the doubters, but I hope I can sway the undecided. Filters are inexpensive, there's a bloke in the outer reaches of Scotland who stocks CAV and line filters at excellent prices - and much more besides.

 

[pvb]

After an unpleasant experience with fuel bug some years ago, I cleaned my tank and have dosed with Startron every time I fill up. I also have twin primary filters, individually switchable, and I've fitted a vacuum gauge. Rather than religiously changing filters every XX hours, I now just switch to a clean filter whenever the vacuum gauge indicates that the filter in use is started to get clogged, and change the dirty filter as soon as I can.

 

[dt4134]

I've had a problem with a fuel filter. Engine would stop or 'blip' then get going again. It would run OK in tick-over. Thought it might be an air leak at first, but then changed the primary filter which didn't solve the problem.

Changed the secondary filter which did solve it. The filter wasn't full of gunk; the fuel in it was just a bit murkier than clean fuel, so interesting to see LateStarter's explanation for that.

The filter had last been changed about three years earlier.