Changing Fuel Filter

[MIDNIGHT RIDER]

as it's not like an oil filter where you are feeding the output into the engine over and over.

Just my .02 worth.

You are sort of correct and sort of not.


The engine only burns maybe 5% at most of the quantity of fuel being delivered to the injector-pump.

That other 95% cycles through the fuel-lines and all filters, over and over, getting filtered at least twenty times before actually getting into the cylinders.

 

[OLDBULL8]

You are sort of correct and sort of not.


The engine only burns maybe 5% at most of the quantity of fuel being delivered to the injector-pump.

That other 95% cycles through the fuel-lines and all filters, over and over, getting filtered at least twenty times before actually getting into the cylinders.

The fuel from the lift pump thru the system is partially returned to the tank thru an orfice at #8 cyl., the return line to the filter at #1 cyl. is mainly to bleed any air to the filter so it can be bled off thru the schrader valve on the filter.
To bleed the air, the schrader valve can be opened a small amount, then with a clear hose going into a can so you can see the bubbles (air), turn the engine over until fuel runs clear, remove the hose, tighten the schrader valve and your good to go.

 

[lotzagoodstuff]

You are sort of correct and sort of not.


The engine only burns maybe 5% at most of the quantity of fuel being delivered to the injector-pump.

That other 95% cycles through the fuel-lines and all filters, over and over, getting filtered at least twenty times before actually getting into the cylinders.

You are correct, and I really like and appreciate your polite response. Too many bad responses and unreasonable hostility on OB lately, but your response is both polite and technically sound.

I guess my real point is that changing a fuel filter when the light isn't on is a waste of money. Although excess fuel does recirculate, there is no bypass on the filter, so if the lights not on, the fuel getting to the IP is "clean".

Does that make sense or am I not understanding the fuel system completely ?

 

[gatorman21218]

What light are you referring to?

 

[lotzagoodstuff]

The "fuel filter" light, which means the pressure drop accross the filter is indicating that the filter is plugging. There's a light for "water in fuel" too, at least on an OBS, I don't know the other models well enough to say for sure.

 

[MIDNIGHT RIDER]

You are correct, and I really like and appreciate your polite response. Too many bad responses and unreasonable hostility on OB lately, but your response is both polite and technically sound.

I guess my real point is that changing a fuel filter when the light isn't on is a waste of money. Although excess fuel does recirculate, there is no bypass on the filter, so if the lights not on, the fuel getting to the IP is "clean".

Does that make sense or am I not understanding the fuel system completely ?

I believe you are in complete understandment.

What light are you referring to?

The earlier trucks had no light; only a water-in-fuel light.


Later trucks must have some sort of filter monitor light.



The best filter monitoring device is a mechanical pressure gauge on the outlet side of the filter; when the "normal" pressure drops a few PSIs, it is probably time for a filter.

Even better is two gauges, one each side; thus, one knows at a glance if a fuel issue is the filter or something else.

 

[gatorman21218]

I have two fuel gauges! I must need to bleed them though b/c my inlet always reads lower than the outlet

 

[MIDNIGHT RIDER]

You are correct, and I really like and appreciate your polite response. Too many bad responses and unreasonable hostility on OB lately, but your response is both polite and technically sound.

I try to always be polite and courteous; however, often meanings can be mistaken when one has no eye contact with the "speaker".


Me not being very eloquent, sometimes what I type is not exactly what I mean.

 

[MIDNIGHT RIDER]

I have two fuel gauges! I must need to bleed them though b/c my inlet always reads lower than the outlet

That is most likely just variance between the two individual gauges; no two are exactly alike.

It should really be the other way around; inlet pressure just a little higher than outlet.


Were I you, I would just establish what readings are "normal" with a clean new filter; maybe even write them down somewhere in the truck.

 

[87crewdually]

Were I you, I would just establish what readings are "normal" with a clean new filter; maybe even write them down somewhere in the truck.

On all my gauges I mark the face with a paint marker to show a reference mark of "normal operation". That way it's just a glance instead of concentration trying to read gauges.

 

[MIDNIGHT RIDER]

On all my gauges I mark the face with a paint marker to show a reference mark of "normal operation". That way it's just a glance instead of concentration trying to read gauges.

On such gauges that actually have a "normal" reading, I orient the gauge in it's housing such that the needle points straight up to "normal".

It is not the most aesthetically pleasing to look at, but a lot quicker to read in the dark.

 

[Worstenemy453]

To be honest, even if i had a fuel filter light, i wouldnt trust it. The sensor might be 24 years old or whatever.

 

[rjjp]

According to alldata (yes alldata has been wrong many times before, so take this with a grain of salt) the light was supposed to come on when the outlet pressure gets down to 2 psi, which to those who understand the DB2 is low. Our injection pumps use fuel pressure to regulate the timing therefor the difference in fuel pressure to the pump would effect our timing and cause a performance and economy loss... I'm only speaking in theory here I've never waited for my light to come on to change the filter, usually when it begins to start hard I pull into the barn and change it.

 

[A_G]

im changing mine also tomorrow but didnt want to make a new thread.

Im going with a one piece filter for the simple fact that i think the two piece is a pain in the ass and mine leaks anyways, in fact i see alot of them that leak. so im going to spend the extra dough and save myself the trouble

But i did notice after a search thats theres one with a sensor and one without the sensor hole. I have a 91, i took a quick look before i headed off to the store i have no hole in my stock filter so no filter with hole in it, unless there some kind of relocation?

Im changing mine for the simple fact is, its leaking, two i dont when the last time its been done, 3 im doing oil to (somebody wrote 12qts of 30wt on the fan shroud) so with seing that im changing filters tmrw oil it needs to be done.

 

[Worstenemy453]

im changing mine also tomorrow but didnt want to make a new thread.

Im going with a one piece filter for the simple fact that i think the two piece is a pain in the ass and mine leaks anyways, in fact i see alot of them that leak. so im going to spend the extra dough and save myself the trouble

But i did notice after a search thats theres one with a sensor and one without the sensor hole. I have a 91, i took a quick look before i headed off to the store i have no hole in my stock filter so no filter with hole in it, unless there some kind of relocation?

Im changing mine for the simple fact is, its leaking, two i dont when the last time its been done, 3 im doing oil to (somebody wrote 12qts of 30wt on the fan shroud) so with seing that im changing filters tmrw oil it needs to be done.

I dont know when the last time mine was changed either, since i bought this truck with only 94K miles on it i am going to keep a complete maitnence log so if i ever do sell it, i have documented repairs and upkeep from 94K. A little piece of mind.