By Pass Oil filtration

[NAM VET]

I was just reading the Oct issue of Military Vehicles, which has a long article on older vehicle engine oil filtration. Several times, the author mentions that our M37 by-pass system is always filtering oil, even at low oil pressures. I thought that our system only by-pass filtered with the pressure at a bit over 40 psi or so, regulated by the spring/plunger in the block. When my engine eventually gets good and hot, which can be over 90 degrees here in SC, (it will take at least 30 or more minutes for to warm up every thing and give a stable oil pressure) my hot pressure at my 40 mph cruise is about 36 PSI or so (RedLine 10-40) and has not changed in the thousand miles or so since the rebuild. My cold pressure is about 58 psi, presumably from the plunger or some other controlling feature. As my pressure slowly falls from a cold start to a stable cruise psi, being less than 42 psi, I fret about the lack of filtering of my oil. By the way, I have an Autometer pressure gage plumbed into the stock gage site. My gage is on my steering column, for easy and accurate reading.

The other day, noted my Autometer gage had a little needle flutter right about 40 psi, which then returned to a stable needle once the pressure dipped into the high 30's. I think this was because the spring/plunger was transitioning from one flow to another.

By the way, with installation of a matching temp sender and new gage, my engine runs 180 to 190 (ambient temps 90+) now with the 180 thermostat. Reassuring to me.

A simple question then, does our by-pass always filter or only at above 40 psi?

Thanks as always, NAM VET aka Hal Copple, UpState SC

[Odie Greenwagon]

Hal
I read your note, with interest. I have had a similar question. You described filtering as it is worded in my manual. My summary, oil-flow thru filter (only) occurs with oil temp above approx 135oF and the relief valve open, it opens at approx 46 psi. I think that is summarized correctly. I do not have nice accurate gauges plumbed up, I have the standard issue SWs. Improved add-on gauges are in my long to-do list. I will keep my standard gauges.

My truck is a new acquisition for me, an old '53 in generally very good running condition. I am not clocking much road miles at the moment, so I am running engine regularly, and changing the oil by calendar.

At the moment, I have no idea how much circulation is taking place thru the filter. During the next weekly warm up, I will make it a point to check the temps in the oil lines to/from the cannister, to get a general idea of oil flow thru the cannister. That is my first step.

Any comments or suggestions you have are appreciated.

Regards.
B

[NAM VET]

going back and re-reading information here about the by-pass filtration on our M37;s, it appears that the writer of the article in the magazine is just wrong about the system always filtering oil. So I am going to change my oil frequently, with a bit over a thousand on this fill. But most of that is hot cruise, so mostly not filtered time.

Still brutally hot here in SC. NV

[TAK824]

This question has been around various forums for quite a while. In general, what has been summarized is on average around 10 percent of your oil is filtered through the bypass filter at any given time. Back in the "day" of bypass systems (anyone remember the Franz toilet paper system?), it was common procedure to change your oil every 3 to 6 months, or every 1,000 to 3,000 miles, 3 thousand being for a daily driver. So filtering was not that big of an issue. Then came the "new generation" of engines, with their "full flow" filtering systems. Now ALL the oil is filtered all the time. And, the oil changes went up to 7 to 10,000 miles or once a year, with better oil today of course. Interestingly enough, I'm restoring a 1962 American Motors "Mighty Mite" jeep, and it has a full flow filter on the engine. Of course, the engine is aluminum and air cooled, so they wanted to protect it well.

[just me]

Just keep in mind that some OEMs didn't bother with filters at all.. The 55 Chevy V8 had no filter at all.
I keep a 1,000 mile oil change interval. My engine is 35 years old and over 60,000 miles. It is starting to get a little tired.

[Cal_Gary]

That would have been the 265 C.I.... predecessor of the 283....
Gary

[NAM VET]

Was recently back in a small town in NE, and went with my brother in law to a pre-sale show of vintage cars. About a half dozen late 40's to mid 50's Chrysler sedans. I closely examined the oiling systems of the flat head motors. All but one had something vaguely similar to our M37 systems, but one engine did not have an oil filter.

I was thinking that an easy way to filter our trucks' oil, is to when the sump pan is off, weld in two AN bungs, then run the in and out AN lines to a remote filter, pushed by a gear oil pump, they are available in 12 and 24V systems. One could add an oil cooler if thought necessary. Then wire the pump to a dash switch, via the truck's battery or batteries. No need to be concerned about what pressure the oil is filtered by the bypass system. If my pan ever comes off again, (being leak free since done by Charles T), I will do such a switchable pump system. Sounds easy to me.

Although I have found nothing is really simple or easy with these old trucks.

All good here in UpStatre SC. Truck running fine and with the new batteries, as always fires right up.

Have a great Thanksgiving with your loved ones,

NAM VET