Prefill Fuel Filters???

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Prefill Fuel Filters???

August 20, 2019, 05:37:47 pm

I'm pretty sure that my 1993 Cummins 5.9 has a mechanical fuel pump and pre-filling the fuel filters (thru the small holes) when changing is the correct way to do it. I have a mechanic who wants to put them in dry and use an electrical pump near the engine which I believe only exists on later year 5.9 Cummins engines. Am I correct? Any thoughts are welcome.

Re: Prefill Fuel Filters???

Reply #1 – August 20, 2019, 05:47:01 pm

I always pre fill my fuel filter, never had a problem the Detroit always starts.

Re: Prefill Fuel Filters???

Reply #2 – August 20, 2019, 06:07:53 pm

Quote from: Dakota Slim – August 20, 2019, 05:37:47 pm

Am I correct?

Yes.

Re: Prefill Fuel Filters???

Reply #3 – August 20, 2019, 06:11:55 pm

Andy and I have a hand priming pump on our U300 so I always leave the secondary filter about a turn loose and then use the hand primer to pump diesel through the primary filter, the lift pump and then fill the secondary until diesel comes out and there are no more bubbles. The engine starts right up after that.

So, unless you have an electric or hand pump, manually filling them will work but you run the risk of not getting all the air out of the lines and also the possibility of introducing some contamination into the injection pump since you are not filling with filtered diesel (yes, the diesel out of the tank should be filtered but the container you are using may have small amounts of contamination). If I didn't have a hand pump, I would install an electric pump like Tom Hall did in this link: Tom Hall

This will work in any diesel that has a return line to the fuel tank. Some CATs don't .

Pierce

Re: Prefill Fuel Filters???

Reply #4 – August 20, 2019, 06:32:29 pm

Because of the many differences in fuel injection systems, there is NO "here is how they all work". So, whether there is better to install dry or pre-fill through the small outer holes (the inlets) totally depends on your model.

Some have a manual primer pump (like the engines with Caterpillar engines).
Some have electric priming (like 0ur 2003 Cummins ISL had).
Some have a manual tab on their mechanical pump.
ETC.

Re: Prefill Fuel Filters???

Reply #5 – August 20, 2019, 07:05:58 pm

If you submerge it in a can of diesel right side up, it will autofill. Just wipe off and install. Your call. Wear gloves.

Re: Prefill Fuel Filters???

Reply #6 – August 20, 2019, 07:12:07 pm

Quote from: Twig – August 20, 2019, 07:05:58 pm

If you submerge it in a can of diesel right side up, it will autofill. Just wipe off and install. Your call. Wear gloves.

BUT, most will go in the OUTLET (large center hole).

Far better to pour in small outer holes so you KNOW it has gone through the filter media.

Re: Prefill Fuel Filters???

Reply #7 – August 20, 2019, 07:54:33 pm

Quote from: wolfe10 – August 20, 2019, 07:12:07 pm

BUT, most will go in the OUTLET (large center hole).

Far better to pour in small outer holes so you KNOW it has gone through the filter media.

Welllllll now ya got me scratching my head. It's already filtered diesel when you add it. All of the diesel ends up at the same place. That's how I've done it for years. *shrug*.

Re: Prefill Fuel Filters???

Reply #8 – August 20, 2019, 08:49:21 pm

Quote from: Dakota Slim – August 20, 2019, 05:37:47 pm

I'm pretty sure that my 1993 Cummins 5.9 has a mechanical fuel pump and pre-filling the fuel filters (thru the small holes) when changing is the correct way to do it. I have a mechanic who wants to put them in dry and use an electrical pump near the engine which I believe only exists on later year 5.9 Cummins engines. Am I correct? Any thoughts are welcome.

Cummins tells us to pre-fill the fuel filters with diesel from a clean container. But. For the common rail, electric injector engines the fuel filters are installed dry as another layer of protection against contamination with "stuff." It has to do with the design of the injectors themselves. Not only is the internal design different but the valve cyles several times per firing cycle.

Re: Prefill Fuel Filters???

Reply #9 – August 21, 2019, 12:27:35 am

We had a petroleum refinery engineer attending one of the Diesel RV Club Technical (an FMCA Chapter) sessions.

When someone mentioned filling with "CLEAN DIESEL", he just laughed. He agreed, it was "mostly clean", but advised against assuming there were no 5+ micron particles in "clean diesel".

Filling the filter inlets is safest. The other may well be categorized as "not best practices, but what you can get away with most of the time".

Re: Prefill Fuel Filters???

Reply #10 – August 21, 2019, 10:19:47 am

If it doesn't have an electric pump he will regret putting the filter on dry.. If it does have a pump it sure can't hurt to pre fill the filters.. I've owned and serviced Cummins , Detroit and a few Cats and would never put a dry filter on one..Sometimes have issues anyway but seldom. If it makes anybody feel better then clean the fuel can and keep fresh fuel in it.. I'm older but still open to new ideas of a better way but it will require some convincing proof.

Re: Prefill Fuel Filters???

Reply #11 – August 21, 2019, 10:22:36 am

Common rail injectors will spray somewhere around 2000 times each second including specially timed pulses occurring six times within a tiny fraction of each second on each compression stroke on a 4 cycle. This is why the fuel has to be super clean and such care has to be made on filter changes. Older Bosch P pump engines are more tolerant of the fuel but still a good idea to have a manual or electric priming pump. Much less mess also, especially if it has to be done by the side of the road.

Pierce

Re: Prefill Fuel Filters???

Reply #12 – August 21, 2019, 10:42:36 am

Our 8.3 is the same engine as Slim's - just bigger holes. I warm our engine up to operating temp before changing filters. Pre-fill both filters (through the small holes) and screw them on. BOOST switch on for max starting amps. Engine has always cranked right up, idles rough for a few seconds, then smooths out. Our mechanical lift pump has a (for all practical purposes) inaccessible manual primer device, but I have never used it when changing filters.

Others may have different results.

Re: Prefill Fuel Filters???

Reply #13 – August 21, 2019, 10:43:32 am

For fuel filter replacement in a U225 or U240, the Foretravel manual (Rev 10-91, Section 3) says to pre-fill the filters.
*If you run out of fuel, the system needs to be primed and bled through a 8mm hex bleed screw above the secondary fuel filter -- after pre-filling the fuel filters -- and operate the lift pump plunger until the fuel is free of air AND THEN loosen all 6 injector lines and crank the engine for 30 seconds. If it "clacks" or runs rough, each injector nut must be loosened one at a time with with the engine running, until air is expelled.
It goes on to say "NEVER OPERATE THE STARTER FOR LONGER THAN 30 SECONDS" and allow 2-5 minutes between starter activations.
I have heard that removing a fuel filter and not replacing it with a pre-filled filter immediately can cause air to get in the lines and could require priming and bleeding. I sure hope that isn't the case in my current situation.

Re: Prefill Fuel Filters???

Reply #14 – August 21, 2019, 10:49:16 am

Does it not want to start or these concerns of a future filter change?

Re: Prefill Fuel Filters???

Reply #15 – August 21, 2019, 10:53:04 am

Quote from: Dub – August 21, 2019, 10:49:16 am

Does it not want to start or these concerns of a future filter change?

The mechanic started yesterday and removed the fuel filters. He had no diesel to pre-fill. He is coming back today to finish the job. I went and got some diesel.

Re: Prefill Fuel Filters???

Reply #16 – August 21, 2019, 10:59:22 am

Quote from: Dakota Slim – August 21, 2019, 10:53:04 am

He had no diesel to pre-fill. He is coming back today to finish the job. I went and got some diesel.

I just steal some out of the big coach fuel tank. That way I know it is relatively "fresh". I always have a couple "jiggler pumps" in my garage.

Very handy for many (mostly legal) purposes.

https://www.harborfreight.com/self-priming-copper-jiggler-pump-47334.html

Re: Prefill Fuel Filters???

Reply #17 – August 21, 2019, 11:01:11 am

Even though we have a hand primer pump, I still loosen the secondary pump until all the bubbles are gone when pumping. This way, pumping is easy and while it does take quite a few strokes, it's no big deal. After I tighten the secondary filter, I go back and use the hand pump again to push all the air back to the tank. But the second time is harder as I have to overcome the spring loaded check valve to get the air back to the tank. An electric pump is perfect as it does all the work so you just have to switch it on and wait a minute or two.

Yes, as Dakota says, if you run out of fuel, it's going to be a lot harder to loosen all the fittings at the injectors. And NEVER use ether on a warm engine.

Pierce

Re: Prefill Fuel Filters???

Reply #18 – August 21, 2019, 08:53:41 pm

Quote from: Dakota Slim – August 21, 2019, 10:43:32 am

For fuel filter replacement in a U225 or U240, the Foretravel manual (Rev 10-91, Section 3) says to pre-fill the filters.

This is not "best practices" for the U240. It's Caterpillar secondary fuel filter housing has a manual hand pump for priming. Caterpillar strongly recommends installing (at least the secondary filter) dry and using the manual pump to prime. Nothing (no bleed screw) to open-- air is pushed out return line to tank. Pump will go from very easy (air) to very hard (fuel is non-compressible and pushing against check valve that retains fuel pressure for starting).

This is both Caterpillar recommendation, and I have done this many many times on our 1993 U240/Caterpillar 3116 engine.

I have done this installing both filters dry, but have no issue with installing the primary fuel filter filled, as any small contaminants will be captured in the Caterpillar 2 micron secondary filter element.

As with many things we are into discussing "best practices" vs "what I can get away with 90% of the time, though it may take a few more minutes".

And, with the 2003 Cummins ISL in our last coach, install dry and turn the key to first notch a couple if times to which activates the electric pump to prime. Never a problem.

Re: Prefill Fuel Filters???

Reply #19 – August 22, 2019, 05:50:14 am

In our C8.3 mechanical ..... I prefill the primary Racor FH1000 as it holds about 2 quarts and install the secondary spin on filter dry. Using the hand pump to fill the secondary it doesn't take long to fill and when the pump gets harder to push because the fuel has reached the check valve / pressure regulator I give it about a dozen more pumps to ensure all air is out. The cummins always cranks easily and no worries of contaminates getting to the injector pump.
Just my opinion, only worth what you paid for it.

Re: Prefill Fuel Filters???

Reply #20 – August 23, 2019, 11:30:36 am

Maybe a Cummins expert will comment, I have heard that in order to purge air from the 8.3 with hand pump it is necessary to have key in "on" position so fuel solenoid will be activated? Anyone know if this is true?

Re: Prefill Fuel Filters???

Reply #21 – August 23, 2019, 12:36:21 pm

I don't know the answe to that question Chuck.. Having my manual 8.3 for 1 year I serviced the engine when I brought it home.. Prefilled the filters and it took an hour to get it started.. Since then I found a better way to get to the pump primer ,under the bed vs under the coach..Take a hammer handle and you can easily reach the plunger. I'm about to service it again and it won't hurt to try it with the key on.. There is a easier way to do this than my first go at it..If my primary shows fairly clean I will skip the secondary filter this service. If there is trash or water will change both..Drained a small amount of trash with routine peacock drain but zero water.. Maybe will have an answer to you question in coming days.. I will continue to prefill filters until I learn better

Re: Prefill Fuel Filters???

Reply #22 – August 23, 2019, 01:16:58 pm

Quote from: Chuck Pearson – August 23, 2019, 11:30:36 am

Maybe a Cummins expert will comment, I have heard that in order to purge air from the 8.3 with hand pump it is necessary to have key in "on" position so fuel solenoid will be activated? Anyone know if this is true?

My answer pertains to the mechanical C8.3 with mechanical pushrod operated lift pump bolted to the side of the block.

On my engine, you do not need the key on to purge air with the hand pump. WHY? Because there is nothing electrical involved in this operation. Fuel pressure at the injection pump inlet is controlled by the overflow valve. This valve is screwed into the side of the injection pump. A fuel line coming out of this valve returns excess fuel to the fuel tank.

The overflow valve is a simple spring-loaded relief valve. When you operate the hand pump, you are pressurizing the fuel in the lines between the lift pump and the injection pump. At "some" pressure (?), the overflow valve opens, and allows fuel (and any air in the lines) to return to the tank.

You will hear the overflow valve make a "squeaking" noise when it opens. When it starts to squeak, you know all the air is out of the lines, and you are good to attempt your engine start.

For more detailed info, see my post (Reply #7) about the overflow valve in my "Fuel System Science Project" thread:

Fuel System Science Project

Re: Prefill Fuel Filters???

Reply #23 – August 23, 2019, 01:24:02 pm

Quote

I just steal some out of the big coach fuel tank.

That's what I do. I just fill the filter up through the big hole, install it, push the primer button until it won't push anymore and start it up. Never had a problem.
jor

Re: Prefill Fuel Filters???

Reply #24 – August 23, 2019, 03:26:04 pm

Chuck,

Outstanding explanation!

Pierce

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