Draining Fuel Filter - M923a2

[RustyM923]

The top filter (spin on) drains fine, however the larger (lower, black) one only makes a gurgling sound when I try to drain it.

There is a schrader valve on the top...should this be pressed (to allow air in) or pressurized (to force fuel out the bottom) to allow the filter to drain? (didn't see any reference to this in any of the TM's)

Putting (letting) air in the fuel filter canister seems like a bad idea... :/

 

[MarcM35A2]

Yes, it is a bad idea. Air in the diesel lines is always bad. On my truck I only drain the spin on filter. I think the big lower filter is a relict from the 809 Series trucks. They don´t have a spin on filter. So they need the valve on the top to release the air after changing the filter. On my M923A2 I only drain the spin on filter. Open the lower valve and press the little pump on the side of the engine a few times. Close the valve again and that´s it! Worked fine for me!

 

[Floridianson]

Water can cause more trouble than air if it hits the injector tips. I like the old canister as it can and will catch the water and yes you have to let air in the top for the water to come out the bottom.

 

[BKubu]

The older M809 series filter was considered an upgrade if you can believe it! These trucks originally came with just the spin on filter. Most were then upgraded to include a small in-line filter. I have not found any documentation for this, but I believe they found that the little in-line filter and the fairly small spin-on filter were not enough. This has been confirmed anecdotally by guys in the National Guard in two different states. They felt that the in-line and spin-on filters clogged too easily. They retrofitted the M809 series filters onto the M939A2 trucks. In fact, there was a kit available to do just that (John Winslow had a bunch a few years back, but I never bought one...I wish I had). Many of the M939A2 trucks were upgraded with the larger M809 series fuel filter. I have found that some of the rebuilt trucks have this, but not all. I have a rebuilt M923A2 that came out of Red River without the M809 series filter.

 

[RustyM923]

Water can cause more trouble than air if it hits the injector tips. I like the old canister as it can and will catch the water and yes you have to let air in the top for the water to come out the bottom.

That makes sense. However, what do you do to get the air out of the filter? I'm imagining that ending up in the pump eventually and stallling the engine (or do I worry too much?)

Thanks for any insight. It's all helpful to me!

 

[RustyM923]

I just realized from reading the TM that the CTA8.3 is assumed to only have ONE filter/separator (the upper spin on one). That's why it doesn't mention opening the air release, as it does on the M939 and M939A1 specs. It seems to be true that they added this giant filter at some point.

I've recently replaced the larger (drop in) and smaller (upper/spin-on) filters. It was a real chore to get her fired back up. Pumping only did so much. There was foam in the pump and I had to crack the inlet banjo fitting to let all that out while cranking.

 

[BKubu]

I just realized from reading the TM that the CTA8.3 is assumed to only have ONE filter/separator (the upper spin on one). That's why it doesn't mention opening the air release, as it does on the M939 and M939A1 specs. It seems to be true that they added this giant filter at some point.

I've recently replaced the larger (drop in) and smaller (upper/spin-on) filters. It was a real chore to get her fired back up. Pumping only did so much. There was foam in the pump and I had to crack the inlet banjo fitting to let all that out while cranking.

You probably did this, but, if not, I suggest filling the filter with fuel before you put it on.

 

[RustyM923]

You probably did this, but, if not, I suggest filling the filter with fuel before you put it on.

I did fill the small one to the brim with filtered fuel and the larger one most of the way up (within an inch...it will spill too easily, IMHO).

I still had to pump forever to get a prime!

Does anyone know what line to pull to pressurize (2psi?) the tank to force the fuel where it needs to go? This would be very helpful for next time.

 

[wreckerman893]

Many of the M939A2 trucks were upgraded with the larger M809 series fuel filter. I have found that some of the rebuilt trucks have this, but not all. I have a rebuilt M923A2 that came out of Red River without the M809 series filter.

There seems to be no rhyme or reason as to which trucks got the big filter. I have three M900 A3 series trucks in the yard and only one of them has the big filter. They may have been installed on trucks that were more likely to be used in dusty environments. DAMIFINO.

 

[73m819]

The big filter was used on the 939 at first, a carry over from the 809s, these trucks had the same engine as the 809s, then the little filter, then the spin on, some 939s have all three, others have just two of the three, others have only one, it seems that the newer the truck, the less filters, just the little one and the spin on, almost like the spin on was a after thought.

 

[CPDOG]

hi

I have that same set up on my m923a2. but the valve has had its valve stem removed and capped (fuel free flows thru valve body from the tank). the filter still functions as advertised.
does anyone happen to have the correct filter part # for it? wix, fram etc.

thank you all for the assistance

 

[74M35A2]

I have an M925A2 (Cummins 8.3L), with both small and large filters. My large filer does the same gurgling if opened, and as others have said, yes, when you push the Schrader valve at the top, the canister drains quickly. This small amount of air in both filters seems to have no effect if your hand priming pump works. Drain into a clear bottle to see if there is water.

 

[5tonman1971]

hi

does anyone happen to have the correct filter part # for it? wix, fram etc.

thank you all for the assistance

There is a sticky post at the top of the forum board that has a the filter numbers.

 

[LiqTenEXp]

if you are looking for the big filter make sure to look up WIX PN 33401 not 44301 if you plan on using that part, there is a typo in the spreadsheet.

 

[PureMayhem]

I just changed my large filter on my M923A2. I opened up the drain valve on the bottom to drain it and nothing happened. I didn’t have a schrader valve on the top but there was a T in the line on the outlet side with a pipe thread plug used as the air inlet so I loosened that and still nothing. I removed the plug completely and still nothing. I took a rubber mallet and banged on the filter cover and slowly diesel started dripping out. When I had drained about half of the diesel I unscrewed the retainer bolt but couldn’t get the cover off. I screwed the bolt back in about ¾ of the way and then had to bang on it with a rubber mallet to get the filter cover to drop down. When I got the cover off and drained the remainder of the diesel there was a lot of crud, rust and dirt that was down in the bottom and had blocked off the drain valve. There wasn’t any water though. I also replaced the fuel line between the large filter and the primer pump as it was cracked and kinked. Based on what was in the large filter I am glad that there are two filters in line. When priming I loosened the banjo bolt and would get squirts of air foam mixed with streams of diesel and that seemed to speed up the process. You do, as I have read in other threads hear a squishing sound in the injector pump when the diesel reaches it.

 

[MO MV man]

I just replaced my fuel filters last week.
WIX 33401 for the big filter. It included the correct large canister gasket AND the o-ring for the screw.
WIX 33472 for the engine-mounted small one.

 

[LiqTenEXp]

The small one is located where on your M931A2?

 

[RustyM923]

The small one is located where on your M931A2?

Left side of the engine. Upper rear side.