Engine oil pressure

While driving my M35A2 n my trip of 870 miles to it's new home the engine oil pressure pegged out at about 2300 RPM with the engine temp in the normal range for cruising down the road. At idle the RPM fluctuates from mid-range to pegged out after pulling over at an exit.
The engine ran fine the whole time, no over pressure issues, and no leaks, and normal water temps.
I am prone to suspect the electric sending unit first but with the price of the gage and the sending unit exceeding 115 minus shipping I am also inclined to put in a wet gage that looks correct for the truck. I did disconnect and reconnect the wiring at the gage with no affect.

Thoughts & suggestions are most welcome.


jimm1009
Jim

Make sure the gauge housing is well grounded.

maybe change the oil and the filters? Then see.

Get a mechanical gauge onto the block (oil gallery ) near the starter and see what's what with the actual oil pressure. Cheaper/easier/quicker to get a single mechanical gauge on there than plumbing a wet gauge into the dash?


Sent from my SM-G950W using Tapatalk

There is a 1/4" NPT plug under the oil filter housing that is the actual oil pump pressure. I have tapped into that along with the one on the passenger side which is pressure reduced. That way you can tell if the pressure valve is working properly.
The main galley pressure is around 100 PSI. The reduced pressure is around 30PSI.

As mentioned, When you can, replace the oil pressure gauge with a (Relatively inexpensive), capillary gauge.
Trustworthy, same looks. And 'What you see is what you got'.
In fact, I have replaced the temperature and oil pressure gauges on all my trucks with capillary gauges.

Hey over there dmetalmiki,
Where did you hook up your wet gage to the engine?
Did you remove the electric sensor and attach it there or somewhere else?
Is your gage a 80 PSI unit?
Thanks in advance.
jimm1009

I see that I might not have described my location well...
On the passenger side, at the very rear of the engine block is a pipe plug, just above the starter.




Rusty's location might be easier to access. I had the engine out!

rustystud said:

There is a 1/4" NPT plug under the oil filter housing that is the actual oil pump pressure. I have tapped into that along with the one on the passenger side which is pressure reduced. That way you can tell if the pressure valve is working properly.
The main galley pressure is around 100 PSI. The reduced pressure is around 30PSI.

Click to expand...

cattlerepairman said:

I see that I might not have described my location well...
On the passenger side, at the very rear of the engine block is a pipe plug, just above the starter.


View attachment 758197

Rusty's location might be easier to access. I had the engine out!

Click to expand...

So if I'm reading this correctly, where Rustystud suggested under the oil filters I should get about 100 PSI reading and where Cattlerepairman suggested I should get about 30 PSI (or whatever my gauge on the dash reads), correct? I'm curious to know more on the pressure reduction and how it works and why. Links please! Thanks.

Deplorable1 said:

So if I'm reading this correctly, where Rustystud suggested under the oil filters I should get about 100 PSI reading and where Cattlerepairman suggested I should get about 30 PSI (or whatever my gauge on the dash reads), correct? I'm curious to know more on the pressure reduction and how it works and why. Links please! Thanks.

Click to expand...

You can find the answer to the oil pressure in the TM's. Basically the oil pump is designed to supply all the pressure the engine could ever need. The problem is most parts in an engine do not need 100 PSI pressures, so the engineers installed a "pressure relief valve" that reduces the "main line" pressure to 30 to 40 PSI. With a 100 PSI backing the relief valve you are always assured of a good 30 PSI "minimum" pressure at all times.
This relief valve is located directly under the "Turbo" on the block wall.
If I have time later I will post the oil diagram showing this valve.

rustystud said:

You can find the answer to the oil pressure in the TM's. Basically the oil pump is designed to supply all the pressure the engine could ever need. The problem is most parts in an engine do not need 100 PSI pressures, so the engineers installed a "pressure relief valve" that reduces the "main line" pressure to 30 to 40 PSI. With a 100 PSI backing the relief valve you are always assured of a good 30 PSI "minimum" pressure at all times.
This relief valve is located directly under the "Turbo" on the block wall.
If I have time later I will post the oil diagram showing this valve.

Click to expand...

Thanks Rustystud, your explanation was much simpler than thumbing through TM's. I never can seem to find what I'm looking for cause I always get side tracked with reading something interesting while searching. Thanks again.

Deplorable1 said:

Thanks Rustystud, your explanation was much simpler than thumbing through TM's. I never can seem to find what I'm looking for cause I always get side tracked with reading something interesting while searching. Thanks again.

Click to expand...

Us "Deplorable" ones need to stick together !
Here's that diagram I was referring to.

View attachment Scan0161.pdf