Sudden Low Oil Pressure
 

'84 - 240D, 255K

Changed oil 1.5 weeks ago - normal running before & after.

Yesterday on cold start - 8 lb pressure at idle instead of pegged. Went up to the peg when drive; sagged back to 5 lb at idle.

I thought maybe I left the old 0-ring in the filter housing - opened it up tonight -- no extra o-ring, nothing I could see or feel at the bottom of the housing. Put it back together with no filter, started it, same low pressure symptoms. Tried blowing in the open end of the center filter shaft -- could get a little oil out of the hole near the top if I blew really hard. Tried to chase the shaft with a cooking skewer that started in fine, but hit an obstruction maybe 2" in; feels like it was made that way. I have no access to compressed air at the moment.

Put the filter back in with a new o-ring & started it -- same symptoms. Oil is full (originally thought maybe the filter o-ring leaked, but no sign of that) with no sign of contamination.

Any ideas??

Sorry for the double post.

Inside of the oil filter shaft that is attatched to the shaft there may be a 1 way check valve. If you are going to blow it with an air gun blow into the small hole that is up near the top (filter cap).
See if your can find your engine on this site and take a look at the oil system.
http://www.pauldrayton.com/uploadfiles/merc/Service/W123/Main.html
When you changed your oil did you also change the Wt (viscosity)?
Do you have a mechanical gauge or and electric one?

Thanks for the drawings,

I think the gauge is electrical ... I can always pray for a plugged sending unit.

Same oil as always -- 15-40 Delvac.

That should be a mechanical guage. the line going to the guage is just plastic. perhaps you have a kink in it. I would unscrew it at the filter housing end and try to attach a guage at that point and see if I have oil pressure there.

Tom W

Thanks, Tom, I'll try that.