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Old 11-04-2015, 08:03 AM   #1
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Why NOT to pre-fill fuel filter?

Just got done with changing filters again (algae ), and I question why we're not supposed to prefill them first?

Seems to me that it would much less work for the pumps/engine to get the fuel up there quicker. And each time, I hold my breath til it finally catches after the turn-wait-turn-wait key-cycles while the lift-pump does its thing, and then the engine flips and flops like it's going to jump off the mounts til it gets a good shot of fuel and smooths out.

The local diesel-guy said he always prefills as it's less stress on the now-unlubricated engine parts, according to him. Talked to Cummins and they just said to follow what's in the book (don't prefill).

I want to do what the mfgr says is right, but would like to understand why. (Dumping air vs opening slides first is another mystery to me, but that discussion will wait til another time ).
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Old 11-04-2015, 08:15 AM   #2
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I always prefill. Easy to do. I use Fleetguard filters and they come with a plug for center hole for pre filling. My ISL never stumbles after changing filters.
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Old 11-04-2015, 08:23 AM   #3
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Because mechanics have dirty hands. The filters are designed to capture pretty small particles to not damage or clog the pump and injectors. Pre-filling the filter could introduce contaminates into very expensive components.
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Old 11-04-2015, 09:04 AM   #4
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As Bob just stated the filter is stopping things you can not see with your eye, pre fill
is a bad idea.
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Old 11-04-2015, 09:09 AM   #5
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Why would you need to? It's not an oil filter. The engine just won't start as fast as a full filter. And yes, the open part of the filter is the gas area that goes to the engine.
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Old 11-04-2015, 09:37 AM   #6
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Quote:
Originally Posted by RWeigant View Post
Why would you need to? It's not an oil filter. The engine just won't start as fast as a full filter. And yes, the open part of the filter is the gas area that goes to the engine.
Of course it does...how else could you attach it to the engine?

It's my understanding that the holes around the outside edge of the filter is where the fuel goes "into" the filter from the fuel tank, and the hole in the center is where the fuel goes "out" of the filter to the engine.

Since I always do my own oil/fuel/air filter changing, I have always put fuel/oil into the new filters prior to installing them. I'm very careful to insure that no contaminates are introduced into the filter while doing this. As mentioned, the Fleetguard filters come with a plug for the center hole to insure the new fuel/oil does not bypass the filter elements. Once the filter is full, I remove the plug and very carefully install the filter.

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Old 11-04-2015, 09:38 AM   #7
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Quote:
Originally Posted by BFlinn181 View Post
Because mechanics have dirty hands. The filters are designed to capture pretty small particles to not damage or clog the pump and injectors. Pre-filling the filter could introduce contaminates into very expensive components.
1st time I have ever heard or thought of this, makes perfect sense.
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Old 11-04-2015, 10:07 AM   #8
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I prefill the primary filter run engine, shut engine down and then change secondary filter. I do not prefill the secondary I use prime pump on engine to fill secondary.


If you do this any contaminants introduced in the primary filter will be caught by the secondary filter and discarded before you install the new secondary filter.
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Old 11-04-2015, 01:16 PM   #9
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I have spent 40 years in the HD truck and diesel business. It's common practice to prefill fuel filters. you will do more damage to the starting system cranking it than you will getting dirt in the filter. Wipe your hands first
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Old 11-04-2015, 03:40 PM   #10
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I'm a retired HD mechanic and I always prefill filters unless they have a priming pump.
Some diesel engines if you don't prefill them you won't get them going. Prefilling any
filters make sure not to get any contaminates in them
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Old 11-04-2015, 03:55 PM   #11
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I have a miserable time restarting my 400 ISL if I don't prefill. It can really hammer the batteries and starter. I don't care how many times I cycle my key on and off. It is a miserable start if I don't prefill.

Prefilling is easy and yes, clean your hands and wear rubber gloves. It is very easy to plug the center hole. I pre fill both of my filters.
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Old 11-04-2015, 03:55 PM   #12
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I agree, you can pre-fill a filter as long as you are very careful not to allow any dirt into the filter, using clean diesel fuel to do it. The conditions in many garages don't lend themselves to not introducing junk into the filter, I think that's why it's not recommended by the engine maker.
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Old 11-04-2015, 04:09 PM   #13
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Quote:
Originally Posted by oldguy70 View Post
I'm a retired HD mechanic and I always prefill filters unless they have a priming pump.
Some diesel engines if you don't prefill them you won't get them going. Prefilling any
filters make sure not to get any contaminates in them
Did you wash your hands first? Mechanics have dirty hands you know.
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Old 11-04-2015, 04:19 PM   #14
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Originally Posted by kketterling View Post
I prefill the primary filter run engine, shut engine down and then change secondary filter. I do not prefill the secondary I use prime pump on engine to fill secondary.


If you do this any contaminants introduced in the primary filter will be caught by the secondary filter and discarded before you install the new secondary filter.
X2, just read an article in fmca about changing fuel filters and they recommend doing it just as you have stated.
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