The Great Oil Filter Question

Owners of WDX-WM300 Power Wagons have run into problems when they wanted to replace their oil filter elements.  This has resulted in many discussions on our available Forums.  Sometimes, the thread was fairly short and gave an answer that worked for some.  Then, there would be another thread that gave an answer that did not work for the first group, but worked for others.

The latest Forum discussion is more lengthy than any of the earlier ones and has provided sufficient detail to allow a complete look at this situation.  It is clear there were two different oil filters used on the WDX - WM300 Power Wagons.  The military WC's also are involved.

Starting with the earliest vehicles, SNL G-657 shows that some 1941 and 1942 1/2 ton and all 3/4 & 1 1/2 ton trucks used a "military junior" filter assembly, Part # 920258, with cartridge Part # 921178.  The remaining 1941 and 1942 1/2 tons used filter assembly Part # 677536, with cartridge Part # 677218.  The T118 1 1/2 ton WF-31 used a sealed type filter. 

The following trucks in the Kempner Power Wagon Museum were examined and all had the "military junior" filter assembly, Part # 920258 with cartridge Part # 921178.  WC21 delivered April 1942; WC52 delivered September 1942 (early series);  1947 WDX; 1958 W300M, and M37 delivered January 1953.

Here is the early series WC52.

Some of the filters had the manufacturers' names on them.  The one above was FRAM and the W300M was Purolator.

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The confusion begins with the WDX.  According to the April 30, 1956 edition, the WDX had either a sealed can type filter, Part # 861028; or a replaceable element type filter Part # 1503494. 

The replaceable element pictured on Plate 10-6 in the Parts List is the sock type Part #676575 and the cover is the "T" handle type.  Here's a Clint Dixon photo of that.

Here's the sock type filter with the top removed.

Because I am not familiar with the sock type filter, I'm passing on Clint Dixon's description of its function.

"The sock type seals all around the perimeter. Oil enters from the bottom of the canister and has to flow upward through the sock filter or bypass straight up the center tube when the filter becomes clogged. It was my understanding that the cartridge type flows in the opposite direction. Oil enters the canister on the side near the top and flows downward around and through the filter and out the bottom of the canister. The cartridge can not seal to the sides of the canister, as it can not fit tight like the sock type.

One of the last couple sock filters I bought was one of the newer larger ones. They WILL fit the canister. It just takes a lot more work to stuff it in there. The old correct sized one was pretty much single hand effort. The even older ones from 10-15 years ago had an attached steel bushing with rubber grommet that sealed them near the top of the center tube. The ones since then have changed to a style without a bushing and grommet. They seal with a sock surface to the tube, just like the outer parameter seals with the sock surface to the inside of the canister. The hole in the center of the filter widens at the bottom to let contaminants fall to the bottom of the canister."

Thanks to Clint for his calm analysis and clear descriptions.

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Here's what I know about the "military junior" type filter.  Clint is correct about the oil entering the filter housing at the top instead of the bottom.  Here's the M37 with the top removed.  Oil enters the housing at the fitting on the side and is filtered as it passes from the outside of the filter to the center of the filter.  There, it is collected by perforations in the center pipe.  Filtered oil flows down the center pipe and exits at the bottom of the filter housing.  There are seals at the top and bottom of the filter to hold the filtered oil inside the center of the filter.  The threaded section seen at the top of the center pipe takes the bolt that clamps the cover against the gasket.  

Here's a picture of the top showing the spring that holds the bottom seal of filter element against the bottom of the center pipe.

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APPLES or ORANGES

Here are two different filter systems which each require that the proper filter element is used.  If you have a "sock" type filter housing, USE A SOCK TYPE FILTER.  The NAPA 1011 (or equivalent) appears to be correct.

If you have a "military junior" type filter housing, the NAPA 1100 (or equivalent) appears to be correct.

ANOTHER DODGE MYSTERY:  It is amazing that trucks which represent the entire time span of my collection - early 1942 through 1958 - all were equipped with the same specification oil filters - manufactured by both FRAM and PUROLATOR, and using the NAPA 1100 "Military Junior" filter element.  If Dodge used this set up in 1942 and listed it is the Military Parts List, and continued on through at least 1958, why did they not include it in the WDX Parts List.  And why did they use the "colander and ball of twine" set up while also using the "military junior" set up.