Military Vehicles Magazine • OCTOBER 2019 27
shape. Otherwise you’ll have to make a new one, or visit an auto
parts store to fi nd an oil pan drain plug washer the right size. A
nylon washer will also work, but don’t use a rubber washer un-
less you’re sure it’s compatible with engine oil. Coat the washer
with new engine oil before installing it.
*Install the new cover gasket. Don’t use gasket sealer.
Coat both sides with new engine oil. And never use silicone!
One might be amazed by all the damage I’ve seen silicone gas-
ket sealer do to engines and machinery when it goes where it
shouldn’t be.
Sometimes you can reuse the old cover gasket and keep the
new one for a spare. Preserve it with WD-40 in a baggie.
If you fi nd you have to make this gasket, use heavy gasket
paper. Most common rubber — such as a piece of old inner-tube
— will soon swell up, get fl abby, and leak.
*Tighten the center bolt fi rmly, but don’t over-tighten or you
might distort the fi lter cover. If in doubt as to how tight is tight,
it’s better to leave it a little looser than you might think it should
be. If the gasket leaks under pressure once you start the engine,
tighten it more.
*Now replace the engine’s oil pan plug and fi ll the pan with
new oil to the correct dipstick level.
*Start the engine. Do not rev it up! Wait for oil pressure to
show on the gauge. As soon as it does, leave the engine idling
and check for leaks at the fi lter. Tighten the cover bolt, if neces-
sary. Also check for other leaks, such as around the oil pan drain
plug.
*After the engine has idled a few minutes, shut it off. Wait a
few more minutes, then check the oil level on the dipstick. You
may need to add a bit more oil.
That’s all there is to servicing most HMV bypass type oil
fi lters.
SERVICING SPIN-ON OIL FILTERS
While many people have serviced this type on their civilian
cars and trucks, others have always had their oil changed at a
garage or quick-lube joint. Changing the oil and replacing the
fi lter on their M715, M151, M880, or HMMWV may be a new
experience for these people.
*First, you need a good-quality oil fi l-
ter wrench. There are several types, but a
steel band model usually works better than
a nylon strap type or those that look like
big sockets. Don’t buy a cheap wrench. It
will bend or break under stress.
*Follow the same warm-up procedure
as described for bypass type fi lters, and
remove the engine oil pan drain plug.
*Many people, including a few oth-
erwise competent mechanics, install spin-on fi lters too tightly,
making them lots of fun to remove — which will generally bend
or break cheap oil fi lter wrenches! If your fi lter is on too tightly,
you’ll often fi nd that socket type wrenches will slip because the
fi lter case is only thin metal. Sometimes even good-quality band
or strap type wrenches will crush the fi lter’s case.
Remember, the fi lter unscrews counter-clockwise like a bolt
or nut. A last (and messy) resort is to take something like a long
sturdy Phillips-head screwdriver, pound it through both sides of
the fi lter case — like a joke arrow through somebody’s head —
and twist the fi lter off using the screwdriver for leverage. If the
fi lter is mounted to an aluminum housing, use common sense so
you don’t break the mount.
*After the fi lter is off, wipe the mount with a clean rag, being
careful not to push dirt inside.
*As with bypass fi lter elements, prime your new spin-on so
you’ll have engine oil pressure as soon as possible after start up.
Also as with bypass fi lters, priming a spin-on takes time because
the new oil has to soak into the media. Keep adding oil until the
level remains constant.
*After the fi lter has been primed, smear some new engine oil
on its gasket and screw the fi lter onto the mount. For spin-ons
that mount vertically (open end up), this is a clean job. With
fi lters that mount at an angle or horizontally, there will be some
mess when you screw them on. More so if it mounts upside-
down. Just move fast!
Just about every spin-on fi lter has the words, “HAND
TIGHTEN ONLY,” on it somewhere. Usually, this is accom-
panied by, “1/2 turn after the fi lter contacts the mounting base.”
Most of us can’t resist adding another half turn with a wrench.
This practice is usually harmless — only making it fun to re-
move the fi lter next time. Excessive over-tightening can strip the
fi lter threads or even damage the mount, however. The fi lter’s
gasket is designed to swell up a little, and the fi lter will always
be tighter when you go to remove it again, so that extra half turn
we tend to give it really isn’t necessary.
A better method is to tighten the fi lter by hand only. Then
check for leaks or drips after engine startup. Assuming you
primed the fi lter, those drips may only be excess oil and not leaks.
Excess oil will stop dripping after awhile. A leak will continue.
*After the you’ve installed the fi lter, replace the engine’s oil
pan plug and fi ll the pan with new oil to the correct dipstick
level. Start the engine (do not rev it) and wait for pressure to
show on the gauge.
*Leave the engine idling while you check for leaks.
*Finally, shut off the engine, wait a few minutes, then check
the oil level again.
Hopefully, this covers just about everything you might have
wanted to know about oil fi lter service on your HMV. ✪