Testing external oil pressure relief valve m20b27

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Strummerandjones
Posts: 4
Joined: Feb 23, 2023 12:10 PM
Location: York,England

Testing external oil pressure relief valve m20b27

Post by Strummerandjones »

Hi ,
I have a m20b27 engine that is suffering from low oil pressure, I have the sump off ,mains and big ends look ok.I am fitting a replacement oil pump but there is also an external oil pressure relief valve. This seems to have a lot of free movement in it before the spring makes contact with the plunger .. is this correct?. I was going to order a replacement as a matter of course but it's no longer available.is there anything I can do to test or refurbish it ?
Thanks
RetiredDoc
Posts: 1316
Joined: Feb 12, 2006 12:00 PM
Location: Aiken SC

Re: Testing external oil pressure relief valve m20b27

Post by RetiredDoc »

Don’t forget the role of the oil filter itself in engine oil pressure. The canister has an internal pressure valve. And sometimes no-name oil filters or counterfeit brand name oil filters don’t have this internal valve at all, and function just like empty cans. You know this already, I’m sure, but just in case someone without your knowledge reads through this thread.

And from my reading and experience there are a lot of counterfeit oil filters out there. Just this year an online store sent me John Deere oil filters for my tractor which turned out to be fake. They looked fine externally but I got suspicious because they weren’t packaged, just loose. I cut one open to check.
gadget73
Posts: 1176
Joined: Nov 22, 2017 10:30 PM
Location: New Jersey

Re: Testing external oil pressure relief valve m20b27

Post by gadget73 »

I don't know these engines at all, so take this with an alarming amount of salt

that said, every pressure relief valve I've ever dealt with had a spring pushed against a ball or plate or plunger with no play. The pressure in the system overcomes the spring and un-seats the whatever in order to let it work. Gut feeling is that if yours is flopping around loose, thats probably not correct.

Pics make me suspect its got typical construction. From the outside it looks like it screws into something, and its got a hole in the side where excess oil would dump out of when it un-seats. If thats what yours is, I suspect you could rig up a test rig using air pressure. Need something the relief valve will thread into which you can connect to an air compressor with a regulator and a pressure gauge. Wind up the pressure and see where it un-seats. There is probably a spec in the manual somewhere.
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