M170/M38A1 Oil filter Lines

rdsar2k · Post by **rdsar2k** » Wed Sep 30, 2009 9:22 am

Is there a flow restrictor in the oil in line to the filter?

The reason I ask is that there is one on my oil line that I took off the engine when I started my overhaul. It is inserted in the fitting reducing the size down to about 1/16" or less.
I need to preface this with what I found on this M170 during dissassembly. The oil had coagulated in the bottom of the pan to a consistancy of thick mud; It would not pour or flow and covered the oil intake filter. Someone (I would guess) had tried to start it and noted the low to no oil pressure and made attempts to correct the issue by changing the oil pump out with an aftermarket pump made by Mellings. Also, the oil filter lines are not original and it could be a bubba mod to have put a restrictor in the line to try and raise pressure. There is nothing unusual about my engine so standard parts apply. If there is suppose to be a restrictor I'll probably reuse the hoses. I've already inspected the pump based on info and gaskets recieved from Mellings Pumps and it is like new so I will be reusing it.

So, does your oil line have a restrictor in it?

Thanks

rdsar2k · Post by **rdsar2k** » Thu Oct 01, 2009 7:47 am

After reviewing information and opinions wherever I could find in web searches, I've decided that the restrictor is a good thing.
The hose is in good condition and the restrictor looks like it is built into the hose fitting; not a bubba mod. The filtration system on these is not an inline filter system but a secondary system that filters pump discharge oil and returns the oil to the sump. High flow to the filter could starve crank/cam bearings in the front of the engine at low RPM. The restrictor will slow the flow to the filter but still allow flow to the gears that the filter discharge supplies on it's return path to the sump.
I guess I've come to conclusion on my own as I've hit the "no response zone" in my post.

Post by **wesk** » Thu Oct 01, 2009 4:14 pm

This is my favorite reference for the L134 oil system.
http://www.g503.com/forums/viewtopic.ph ... 4&start=15

Tony says it all there.

idiocrates · Post by **idiocrates** » Fri Oct 02, 2009 12:45 pm

That is about as good a discussion on oil lubrication systems as I've ever seen....although I have to admit to not being the most well read person around here.....fur shure. Wish those guys were still around cause I also have some questions......like......so which do we want.....high pressure with a restricted volume......or low pressure and high volume? Is the whole idea around having a pressure gauge just to "show" you that the lubrication system is working? And isn't the oil pump on a 134 engine a gear pump? Gear pumps are positive displacement....which means as long as there's something to pump....if there's no bypass valve or open outlet....the pump will continue to buid up pressure until something gives.....aka.....busts.....or the pump bypasses internally....usually destructively. So I'm not so sure messing with the bypass is such a good idea. All in all though I really enjoyed reading the discussion.....even the parts that were in latin. hehehe....

Post by **wesk** » Fri Oct 02, 2009 10:40 pm

Your pressure vs volume (flow) questions are just semantics. Each relies on the other and the trick is to set up the system so you get the best of both numbers. Pressure will insure quick delivery and flow will insure adequate film developement to support seperation of the friction producing parts and adequate flow also helps with oil temperature control.
Aircraft and high performance applications will usually gage and monitor both oil temp and oil pressure. Most don't bother with flow gaging since those accurate flow meters are quite expensive.

The results of no relief or bypass with a gear type pump is as you say. The decision to use a gear type, vane type or piston type pump depends on the needs of the system. All three regulate pressure by relief in some form. Keep in mind that flow restrictions creates pressure and relief only prevents that pressure from getting too high. Many folks like to think the system or pump relief valve "regulates" pressure but that is not true for example a relief valve set at 45 PSI will not function if the offered resistance to flow only creates 40 PSI of pressure.

Sadler5 · Post by **Sadler5** » Sat Oct 03, 2009 8:24 pm

I know this question has come up before and has been discussed - flow versus pressure etc. The web link that you posted here is invaluable. I have turned it into a pdf and will reference it in the future.

The information that is provided on this web page helps all of us. I see some of the same questions asked over and over and the people that answer them continue to exhibit patience with novices such as me. My hat is off to all of you that take the time to explain solutions to the problems we encounter and to lead us down the correct path to keep our fine machines running.

Keep up the good work.

M170/M38A1 Oil filter Lines

M170/M38A1 Oil filter Lines

Restrictor