I recently transplanted an engine into my daughter's '91 240. The engine came out of an '89 240 that had 173k miles on it when my son totaled it. We had bought the '89 when it had 30k miles on it so I know pretty much the whole history of the engine. Oil was always changed at 3000 miles and all maintenance regularly performed. However, it did sit in my garage for 5 years without being run.

After putting it in, it seems to run smooth and pull strong - no real issues. Except, for this oil pressure issue. I didn't notice any problems in normal driving. However, I also put all new brake pads and rotors on the car. I took the car out to break in the new pads/rotors which involves multiple increasing hard braking maneuvers. After one of the hard stops, the oil light came on. I immediately stopped and shut off the engine. Checked the oil, looked for leaks, etc. All seemed ok so I started it up and the oil light went off. All seemed good. So I gingerly drove home.

Concerned that this might be a oil pressure sending unit issue, I went out and purchased an oil pressure gauge to verify. Hooked it all up, started the engine up, oil pressure was fine. Somewhere around 60psi when the engine was cold. Took it for a spin and during normal driving it behaved just as would be expected. However, when I did the hard braking maneuvers, the pressure dropped down to 25 psi and stayed down there. If I shut the engine off and restarted it, the pressure went back to normal at around 50psi.

Any ideas that would explain this behavior? I currently am afraid to let my daughter start driving it until I can sort this out.

 

hmmm. I've done all sorts of hard braking and accelerating in my 240s and other B230F(T) engined cars, and never experienced anything like this. I wonder if somethign is funky with the oil pump ? when you brake hard, all the oil in the pan is supposed to shift forward, but the oil pickup is supposed to stay covered even under the worst extremes as its in the bottom of the deepest part of the pan, short of rolling over.

the oil pump is under the crank, its pickup is on the bottom of the deeper part of the oil pan, covered by a strainer screen, its driven by a spiral cut gear that's on the of the counter shaft inside the engine that also drives the distributor if you have the side-of-block distributor (240's mostly as 740/940s have the distributor on the crankshaft).

I suppose if there was some metal junk trapped in the pump, it could somehow block a port or something. Only way I can think of finding out whats going on involves dropping the oil pan.

 

I posted this over at brickboard as well and it was suggested to flush the internals using dexron as a lubricant - idle only. I might give that a try before I drop the pan.

Thanks for the help.

 

I gave the dexron flush a try and it seemed to do the trick. Flushed it twice. I cut open the oil filter to see what it had caught and sure enough it was full of crud. Did the same after each flush. After the second flush the filter was pretty clean. Loaded up the oil and took it for a test drive and the oil pressure stayed up - even with sudden braking maneuvers.