Military Vehicles – October 2019

MilitaryVehiclesMagazine • OCTOBER 2019 25

causetoomuchoilpressurecandamagefrontandrearcrank-

shaftseals,lettingoilleakontotheclutch,andleaveyourengine

lowonoiloutontheroad.

Occasionally,thisvalvemaybecomejammed,especiallyon

vehicles thathaven’treceived propermaintenance andregular

oilchanges.I onceboughtanM37thatalwayspinnedits 60 psi

oilpressuregauge,evenat idle.I thoughtthiswasa typicalmal-

functionofM-seriesgaugesandcheckedit witha mechanical

gauge.It pinnedat 120!Thisexplainedthetruck’sinsatiableoil

consumption—andallofthepuddlesit leftwhenparked.

It’snota goodideatotrytoincreaseyourvehicle’soilpres-

surebystretchingthespringinthisvalveorbyaddingwashers

toit.(This,is a commontrickusedbysomemorally-bankrupt

vehiclesellerstoboostoilpressureina wornoutengine.

SERVICINGA BY-PASS OILFILTER

Whenshould your oilfilter be serviced? Every time you

changeyouroil—hopefully,that’sbeforeit beginstolooklike

tar!Keepinmindthatmotoroilcanlookcleanbutstillbeworn

out.Thisis whyyoushouldestablisha regularchangingsched-

ule.

ForHMVsthataredrivenregularly,3,000milesisa good

intervaltochangetheoilandservicethefilter.Forvehiclesonly

usedforshorttripsandthatnevergetfullywarmedup,moisture

willcontaminatetheoil.Thiswillformacidsthateatawayat

bearingsandcylinderwalls.Forvehiclesusedforshorttrips,you

shouldchangetheoilmoreoften.

Anoldshade-treepracticewastoservicetheoilfilteronly

everyothertimetheoilwaschanged.Thisisnota goodidea.If

youdon’tservicethefilterwheneveryouchangetheoil,you’re

usuallyleavingat leasta quartofdirtyoldoilintheengine.

IfyouhavejustacquiredanHMVwitha bypassoilfilter

and/or have had no previous experience with this type, here is

the service procedure:

*You’ll fi nd that servicing is rather messy compared to the

spin-on full-fl ow fi lter on your civilian car or truck. Have plenty

of clean rags or paper towels on hand.

*As when changing the oil on any vehicle, the engine should

be well warmed-up. Drive it a few miles so all the gunk and

goo is suspended in the oil and not left in the bottom of the pan.

Never drain your oil cold.

*After the warm-up (the oil pan should be hot to touch) re-

move the oil pan plug and drain the oil into a suitable container.

*While the pan is draining, open the fi lter case by unscrew-

ing the large bolt on top. On some fi lters this bolt is removable

from the cover, but on others it isn’t, so don’t try to pull it out if

it doesn’t want to come out.

*Remove the cover. Oil shouldn’t pour out when you do this,

but it’s wise to be prepared. If the cover is stuck, tap it gently

upward with a wrench or small hammer.

*For a minimum of mess, don’t remove the fi lter element yet.

Instead, get a coffee can or other container — one that’s obvi-

ously large enough to hold all the oil in the fi lter.

*Remove the drain plug from the bottom of the fi lter case and

let the oil drain into the can. Wait for most of the oil to drain out

of the element. Five minutes is usually suffi cient.

*Ontheotherhand,if youwantlotsofmess,yanktheele-

mentoutrightnow.Somefiltersdon’thavedrainplugs,soyou’ll

havea messanyway...butat leastit willbea smallermess.

*Didyouconsiderwhereyouwheregoingto putthedripping

Oil fi lter screen on a GMC 270 engine.

Most bypass oil fi lters, such as this Military Standard Junior used on

many common HMVs, function at all pressures whenever the engine

is running. In other words, they are an alternate route for a portion

of the oil to take as it circulates through the engine. Oil is pumped

into them — usually from an oil gallery in the engine block — and

then is dumped back into the pan or timing cover after being fi ltered.

So, even if your WC is only running 5 psi of oil pressure, at least its

bypass fi lter is fi ltering... assuming it has the right element and isn’t

clogged with crud.