MC engine - low oil pressure...Update 2

[E Bavely]

Ben...

Comments below...

>AFAIK off hand, at least for the 4000's, the high pressure 1.8 bar
>switch is in the top position.  That should be the same for all 5 cyl
>motors, <snip>.

Yes, my 4kq engine had the 1.8 bar switch in the top position as well, but
ET_KA shows the same switch in the lower position on the 5kt.  Just for
giggles, I switched my senders in the 5kt motor.... of course, there was no
change in the readings.

>I would not think the pump itself, but maybe the pressure relief valve
>located in the housing, if I recall correctly.  Check to see if you
>have one.

Good thought. That was actually the first thing that I checked.  I took out
the plug, spring and piston and compared it to the one in the 4kq, then even
swapped them.  Springs looked to be the same length, pistons seemed clean
and moving freely in the bore.  No change in the behavior.  A later search
in ET_KA reveals that they should be the same exact part numbers....

Just to confirm though, the "pointed" end of the pressure relief valve does
seat itself against the spring, right?  I'm almost sure that's how it goes
since the open end would have a hard time sitting on the spring.

I just verified the readings (with oil cooler lines capped) on another
electrical oil pressure gauge this morning and got the same results as
before... in fact just a touch lower.  Verified all gauge wiring and
everthing looks to be fine.

One note though...while I was testing, I noticed a kind of rattly type of
bearing noise coming from the front of the engine... seems to be coming from
either the water pump (unlikely...it's brand new) or maybe the oil pump
itself.  It wasn't the nasty type of main bearing noise thankfully...

Whatever it is, it seems to be temperature related, like the pressure
problems.  The engine has the proper pressure when it's first run for about
5 minutes, then when heat gets to it, the pressure drops like a rock and
won't build even when the engine is revved.

Tomorrow, I'm going to test the pressure once again with a mechanical gauge
before tearing into the front of the engine to remove / inspect / replace
the oil pump.

If it's not the oil pump... I'll have to consider other options...

Thanks for your help.

Elliott

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