Fuel Filters on Diesel Engines

[wolfe10]

Fuel Filters

Though this was written specifically for Caterpillar engines, 90 percent of this applies to any DP's fuel system.

The typical "proper" fuel system layout: Fuel tank, primary fuel filter/water separator (course filter element-- 10 or 30 micron), lift pump, secondary fuel filter (2 micron filter element) WITH Caterpillar manual primer pump built into top of filter housing, engine.

With the above system, you buy either a 10 or 30 micron primary filter element and the Caterpillar 2 micron secondary filter element. Install both DRY (per Caterpillar, not just my opinion). Use the manual primer pump to prime. To use

the manual pump, no tools are needed. Unscrew the knurl nut (counter-clockwise). Pump in/out until the resistance goes from easy to firm (this will happen within a few strokes when all the air is purged from the system). IMPORTANT: Re-tighten knurl nut. You are ready to start the engine and drive off.

Now, for chassis where chassis maker took some "money saving" shortcuts:

If no manual primer pump: A Caterpillar manual primer pump can easily be fit if you have a Caterpillar secondary filter housing. It will have a block-off plate attached with two bolts that can be removed and a pump bolted right up. See "Files" section of the Cat RV Club Technical Website for parts list. http://autos.groups.yahoo.com/group/CATRVCLUB/files/.

BUT, until you do that, you MUST pre-fill the filters with clean diesel before installing. Be sure, particularly on the secondary fuel filter to fill ONLY the small outer holes (inlets), NOT the large center hole (outlet). Anything that goes into the center hole will go directly to the injectors with no filtration! Ya, it takes a lot longer to fill this way, but it is safer than "hoping" that you have no contaminants in the fuel (and you can not see a 5 micron particle with the naked eye).

If only a single fuel filter (chassis maker deleted secondary filter to save money), the filter element MUST BE 2 MICRON. Here is the rub. Go into a Freightliner dealer and ask the parts guy for a fuel filter element for a Freightliner motorhome chassis. If the last 4 filter elements that parts guy sold were for the two filter system, IT IS QUITE LIKELY THAT HE WILL JUST HAND YOU A 10 OR 30 MICRON ELEMENT-- it will fit. YOU WILL BE SPENDING BIG BUCKS TO GET THE "ROCKS" OUT OF THE INJECTORS-- ACTUALLY YOU WILL BE REPLACING THEM. By the same token, if you have the two filter system and the last 4 filter elements he sold were for the single filter system, it is quite likely that he will just hand you a 2 micron element. Almost as bad. You now have a two micron element followed by another 2 micron element. The first will clog up quickly and the second will get a "free ride".

Moral: Specify what micron rating filter element you need for YOUR application. BETTER, know the part number for the correct element and ask for that part number.

Unlike most maintenance items, there is NO AVERAGE LIFE for a fuel filter. If all it sees is clean fuel, it could go for years. One tank of contaminated fuel could clog several sets of filters. ALWAYS CARRY AT LEAST ONE EXTRA SET OF FUEL FILTERS. You can find someone to install them virtually anywhere in the world, but may not be able to get the proper filter elements in the boonies. Mark the date on the filters when you buy them so you use "oldest first" and buy a new replacement that goes into your parts bin on the coach.

Our engine’s fuel systems are "HIGH BYPASS". That means that for every gallon of diesel pumped through the engine, only a few ounces are burned. The rest is used to cool and lubricate the head and then returns to the fuel tank. What this means in practical terms is that the next time you stop after refueling you should visually check the primarily filter (those with a clear bowl filter), as dirt and water will show up very quickly if present.

Brett Wolfe

[moyb6dy]

Brett, just reading your article on diesel fuel filters. I always take my motorhome to a freightliner truck repair shop. If they change the filters, wouldn't they install the right filters? Thanks af

[wolfe10]

Brett, just reading your article on diesel fuel filters. I always take my motorhome to a Freightliner truck repair shop. If they change the filters, wouldn't they install the right filters? thanks af

Short answer is "They MAY".

Correct answer is that you VERIFY the correct filters by part numbers. I would call Freightliner (Gaffney) and get the part numbers for your correct PRIMARY and SECONDARY or ONLY filter (single filter systems), request those when you go in for service and verify them before leaving.

As I said above, here is the concern: Go into a Freightliner dealer and ask the parts guy for a fuel filter element for a Freightliner motorhome chassis. If the last 4 filter elements that parts guy sold were for the two filter system, IT IS QUITE LIKELY THAT HE WILL JUST HAND YOU A 10 OR 30 MICRON ELEMENT-- it will fit. YOU WILL BE SPENDING BIG BUCKS TO GET THE "ROCKS" OUT OF THE INJECTORS-- ACTUALLY YOU WILL BE REPLACING THEM. By the same token, if you have the two filter system and the last 4 filter elements he sold were for the single filter system, it is quite likely that he will just hand you a 2 micron element. Almost as bad. You now have a two micron element followed by another 2 micron element. The first will clog up quickly and the second will get a "free ride".

The less ASSUMING and more VERIFYING you do, the better your likelihood of doing the proper maintenance. You will find it easiest to compile a list of fuel filter part numbers, oil filter part numbers, belt numbers all on one quick reference page and use that when you go in for parts. Check with Freightliner, they have have just such a list for your chassis.

Brett Wolfe

[Jackhal49]

I have a Winnebago 05 Journey with a 350 Cat C7 engine. Does this engine have one or two fuel filters??

[wolfe10]

I have a Winnebago 05 Journey with a 350 Cat C7 engine. Does this engine have one or two fuel filters??

Two ways to find out:

Call your chassis maker (Freightliner, I suspect).

Start at the filter you see in the very back of the coach. One line will come from the fuel tank (disappear into the frame rail forward). Trace the other line. It may go directly to lift pump/engine or through lift pump and then to SECONDARY FILTER. You can also raise the bed and look on the passenger's side of the engine for a secondary fuel filter. If you find it, see if there is a manual primer pump at the top of the secondary filter housing (knurl nut 1-2" in diameter).

It is CRITICAL that you find out, as the filter you see will be VERY different if one vs two filter system.

With one filter system, that filter you see HAS to be 2 micron.

With a two filter system, the Primary filter (the one you see in the back) will be either 10 or 30 micron and the Secondary filter closer to the engine will be 2 micron.

[johnnyd]

From the dates on your thread it looks like I'm late to dinner...

I have been looking for info on a problem regarding new fuel filters/engine only runs 3-4 min. after remote mechanic fills both filters with fuel and pumps primer. He repeats the process. Fuel tank is about 3/4+ full. Rear of motor home is elevated with leveling jacks. this engine ran and started perfectly prior to this filter change. Mechanic has 18yrs experience with a local shop,,,, mainly marine engines, but then motorhomes.

He is now pointing to the fuel pump and something that is incorporated with the fuel pump that has some thing to do with creating pressure for the injectors or valves. not sure exactly what he was referring to. I plan to talk to the guys at Freightliner to get their opinion and ideas.

I have a 01 National Tradewinds LTC 39' with a 3126b Cat engine. sn# 8yl 80428. I have a Freightliner chassis and have two fuel filters and a manual primer pump.

My problems is: this mh was running very well, until the filter change... we tried to start the engine as soon as he had changed filters and primed, as pointed out above......

After reading several threads on different sites I'm leaning toward an air lock between the primary filter and the fuel tank...... help....

John Wells

[wolfe10]

John,

Welcome to the FMCA Forum.

Particularly if you jacked up the back of the coach, it would be easy to picture fuel draining all the way back from the fuel filter to the tank, leaving that 20' or so of fuel line with air in it.

But, the manual primer pump should be able to pull fuel through. Certainly, raising the FRONT of the coach rather than the rear would make fuel flow easier.

Unscrew the manual primer pump plunger. Pump it. If easy to pump, there is air in the system. If REALLY hard to pump, it is fuel and you have eliminated this issue. Be sure to screw the primer pump plunger back in when you are finished!

While it could be something unrelated, it would be very unusual for the engine to run perfectly before the filter change and not run well after the filter change and yet be caused by something unrelated.

If the primer pump will not keep the system primed (it will run for a little while and quit and then when you pump the primer pump it starts out easy) there may be a poor seal at one of the filters, perhaps one of the old as well as new gasket was left on, etc.

Brett

[johnnyd]

John,

Welcome to the FMCA Forum.

Particularly if you jacked up the back of the coach, it would be easy to picture fuel draining all the way back from the fuel filter to the tank, leaving that 20' or so of fuel line with air in it.

But, the manual primer pump should be able to pull fuel through. Certainly, raising the FRONT of the coach rather than the rear would make fuel flow easier.

Unscrew the manual primer pump plunger. Pump it. If easy to pump, there is air in the system. If REALLY hard to pump, it is fuel and you have eliminated this issue. Be sure to screw the primer pump plunger back in when you are finished!

While it could be something unrelated, it would be very unusual for the engine to run perfectly before the filter change and not run well after the filter change and yet be caused by something unrelated.

If the primer pump will not keep the system primed (it will run for a little while and quit and then when you pump the primer pump it starts out easy) there may be a poor seal at one of the filters, perhaps one of the old as well as new gasket was left on, etc.

Brett

Thanks Brett.

The seals have been checked and rechecked. Fuel is not getting to the filters. After the engine stops I check both filters, and both are down by half. Its 5:12pm and I'm through for the weekend, unless of course I get a new idea to try. I don't expect to hear from my mechanic till about Tuesday. Will follow up then. However, I will be checking your thread for any new ideas......

Thanks ,,,, John

[johnnyd]

Brett,

To make sure I understand your instructions let me tell you what I am getting out of this.....

If there is an air lock from the tank to the primary filter or in the line from the primary to the secondary filter I should be able to clear this problem with the pump. Is that correct?

Could you possibly have this airlock and not be able to clear with the pump?

I have been filling the filters (as did my mechanic and the Freighliner mechanics do the same thing, then pumping 4-5 times, each stoke becoming harder and harder to complete. When I start the engine it runs very smoothly for about 4 min. then you can hear the engine labor, RPM'S reduce and just before the engine stops I get white exhaust.

If there is an air leak, then it would not clear, but when I pump the aux pump it is very difficult to complete the last 1-2 strokes, which tells me I'm pumping fuel.

Ii think I should just wait till my mechanic gets back to me and see what he has been able to determine from the Freightliner shop.......

If you can shed any more light on this subject, please do so.....

Thanks

John Wells

[wolfe10]

John,

Yes, you should be able to clear any air in the system with the manual primer pump (assuming the system doesn't have a leak). But, the fact that you find the filters half full of air and the manual primer pump easy to operate suggests that air is getting into the system somewhere. And, since even the primary fuel filter is getting air in it, it doesn't sound like an engine issue, since that is "upstream" of the engine or even the fuel lift pump. Wonder if the tech used a pair of vice grips or something like that to shut off the line coming into the primary filter and ended up putting minute breaks in the hose wall. Remember, since this is on the suction side of the system, you may not have any visible leak, as the leak is air INTO the fuel line.

Brett

[johnnyd]

Didn't see him with any pliers, but still possible.

Is there any way for ME to check and detect leaks?

Would the Freightliner shop be able to isolate a leak, or do they just start changing lines, etc.?

[johnnyd]

My mechanic got back with me. His contact at the FL shop says they would try to pump fuel from a separate container, bypassing the lines,filters and, if that works then start trying to fine air leak in the lines,filters etc. My mech. says I have a high pressure fuel/oil pump combo, and if it is the pump, they are very expensive. Being only a shade tree mech, it seems to me that if the high pressure fuel/oil pump was bad, half of the fuel would not be used up and the engine wouldn't run for 3-4 minutes, after refilling. the filters of course. he will have a new short line made up and try to get back over early next week. What do you think about involving the pump-- think there could be a problem there?

Thanks again for your time Wolfe...

John

[wolfe10]

John,

Diagnosing an engine problem over the internet is not realistic.

But, I will say, I DON'T like coincidences-- and the likelihood that a HEUI pump or fuel pump would go out at exactly the same time as the fuel filter change is VERY remote.

My strong suggestion is to take it to a Caterpillar shop, not general mechanic. All they deal with for a living is vehicles with engines just like yours. You don't want to pay for a parts changer to guess at the cause at your expense.

Brett

[johnnyd]

Brett,

I noticed another posting by you under (engine) concerning a filter problem by Jim.....

you noted that cat part number 198-6378 was the correct filter for a single filter system.

I have a two filter system and have been using the same part # filter as by water sep/filter.

after noticing your post, I called my local Cat parts dept and the guy says he doesn't have a separate filter # for a dual filter system.... I know this probably isn't why I am having my problem, but should not Cat have a different filter for my set-up?

[wolfe10]

The chassis maker, not engine maker chooses and installs the primary fuel filter/water separator. Could a Caterpillar or Cummins dealer have the correct one? Sure, but he would have no way to accurately look it up and stocking the correct one for all the different chassis makers (truck as well as RV would require quite a stock).

Check with your chassis maker for the correct primary fuel filter/water separator element. And fitting a 2 micron primary followed by a 2 micron secondary is NOT the way to go. A 10 or 30 micron primary along with the 2 micron secondary properly spreads the filtration duty.

Brett

[johnnyd]

Brett:

Ok, this morning my mechanic showed up with intentions of measuring for a small fuel line to feed the engine with a bucket, to try to locate an air leak. I suggested he try (your instructions in the "engine" section) to pressurize the tank, since this seemed to be the fastest test. He cranked up his compressor and removed the secondary filter. When the tank pressurized and fuel was pumped to the primary filter, it began leaking from the top of the clear plastic bowl. We inspected for cracks, found none, replaced the gasket and … "shazam," no more problem. We reloaded the filters and started the engine, which ran for about 15 minutes, and then it stopped and restarted several more times …. Thank you for your help. I plan to Join FMCA today.

John Wells