M42 Just Rebuilt: Oil Pressure question

[Gerta]

Ok, so I just fully rebuilt an M42 engine for a daily driver - both top and bottom ends went to the machine shop, new gaskets, timing components, oil pressure valve, cooling, etc ... Car currently has about 12 miles on it since the rebuild. Engine has full fluids (i.e. all new fluids - oil is dino Castrol GTX 20w / 50).

Now my questions - On start up I get the standard all lights on the cluster. The issue is the oil light stays on for a minute or two after start up. Is this normal after a rebuild? Does this go away after fully breaking in the engine (~500 - 1200 miles?). My thought is that this might be related to everything not being seated, but my OCD and paranoia won't let it go.

Any thoughts or worthwhile contributions here appreciated.

[jntar]

Is it possible when the parts went to the machine shop they dipped or jetsprayed the parts with the oil pressure sending unit still attached? The chemicals could have shorted the sensor.

[Gerta]

No, all new parts or fully disassembled for cleaning. I have a spare oil pressure sender that I could swap in (known good working), but I thought I might see if there was any feedback first before I start trying to swap out parts.

[jntar]

To my understanding the light should be no different before or after break in. It's possible you're taking longer to build pressure, bot not 2-3 minutes. It should be at full pressure within a few seconds. It could be something simple causing the light. The unit could be bad or a connection wire could be causing the light. It's a quick swap, try out your working one and report back.

[Gerta]

Done. No dice. Still lights up at start and then stays on for about a minute, then shuts off ... seems very related to engine getting up to pressure.

[bmwm42]

Did you bleed the oil pump?

[Gerta]

I did not. No indication of that in any print material I referenced for the build.

I did check my blinker fluid levels and those are ok ...

[bmwm42]

Oil pump new?

[Gerta]

Phil - In an effort to understand what you are talking about could you explain the process?

[Gerta]

No, I reused the oil pump after it was inspected by the machinist (PRO 3 shop)

[bmwm42]

Was thinking about something else sorry Kevin....worst case maybe bearing....also you didn't forget to install the gasket between the oil pickup tube did you?

[Gerta]

Phil - No worries. Car runs too perfect for it to be a spun bearing. I did the internals work at the shop with the owner looking over my shoulder. The oil pickup was cleaned at the machine shop and installed with gasket by me. So I know I did not forget that ... What has been your experience with a new engine? Does it take some time to properly seat where oil pressure is an issue at start up.

First engine I've ever rebuilt so tons of questions and no experience to draw upon.

[ForcedFirebird]

Did you bleed the oil pump?

I did not. No indication of that in any print material I referenced for the build.

I did check my blinker fluid levels and those are ok ...

It's not a bad idea to pack an oil pump with grease or Vaseline, helps keep air out on initial start-up, but you seem to have another problem if it's persisting.

Did the machine shop assemble the engine? What kind of bearing tolerances did you have?

Typically, the oil pressure will be high with a cold engine, then drop as the oil thins out.

Your engine is running dangerously low oil pressure if the light is staying lit, it barely illuminates/flickers at ~8psi (barely enough for idle).

Do you have access to an oil pressure gauge kit? Also check for ground faults on the sensor wire. When the wire is grounded, the light comes on (unplugged defaults to light off).

[Gerta]

@ John - I packed the oil pump with graphite based grease per the machinists recommendation. The machine shop assisted me with assembly (i did the work while he watched / helped). I wanted the experience of building the engine.

All the tolerances were in spec as the crank, block, and pistons were all mic'd prior to assembly. Which is why I am at a loss. I bet it is something simple and will check the grounds on the sensor wire.

[bmwm42]

Ive done a couple nothing with the bottom end....ive never had the oil light come on and when I have seen it and it wasn't the sensor it was always the pump......id give anther try with lighter oil?