NHC250/M939A1 No oil pressure on startup

[Trecker]

Hello together,
I have an M934A1 here in Germany. On motor start I noticed that oil pressure needs at least 10 seconds to start to build up. I the truck was standing for days/weeks it takes even longer.
Investigating this problem I found oil from high pressure side returning throught the pump back into oil pan. The oil filter housing is only filled to a third after some time standing. I could not find any part that could prevent this issue in manuals.
So I have following questions:
1. Is this the time for building oil pressure normal?
2. Is it normal that oil can flow back into the oil pan?
3. What can I do to solve these problems?

Oil pressure is perfectly normal after start-up and under hot conditions, so the oil pump should be ok?

I would be thankful I somebody can help me with this problem!

Greetings from Germany

 

[Mullaney]

Hello together,
I have an M934A1 here in Germany. On motor start I noticed that oil pressure needs at least 10 seconds to start to build up. I the truck was standing for days/weeks it takes even longer.
Investigating this problem I found oil from high pressure side returning throught the pump back into oil pan. The oil filter housing is only filled to a third after some time standing. I could not find any part that could prevent this issue in manuals.
So I have following questions:
1. Is this the time for building oil pressure normal?
2. Is it normal that oil can flow back into the oil pan?
3. What can I do to solve these problems?

Oil pressure is perfectly normal after start-up and under hot conditions, so the oil pump should be ok?

I would be thankful I somebody can help me with this problem!

Greetings from Germany

.
I would hazard a guess that you are just fine.
The gauges in those vehicles are not always "top of the line" either.
You might plug in a mechanical gauge in the oil gallery on the side of the motor - to verify your oil pressure.

 

[Trecker]

.
I would hazard a guess that you are just fine.
The gauges in those vehicles are not always "top of the line" either.
You might plug in a mechanical gauge in the oil gallery on the side of the motor - to verify your oil pressure.

You can hear the motor quieting down when pressure finaly builds up. So I would guess that there is no pressure and the gauge works correctly

 

[98G]

These take a few moments to build pressure.

 

[Trecker]

Is there any way to improve this? Pump and motor always loosing 'prime' does not seem so good.

 

[98G]

Is there any way to improve this? Pump and motor always loosing 'prime' does not seem so good.

While it bothers me also, I think we're worried without cause.

These were million mile engines in over the road usage for decades. If it were really a problem, someone would have addressed it by now.

One solution would be to have an electric oil pump to pressurize the oil prior to starting. I've read about people doing this, but I think it's a solution in search of a problem...

 

[BKubu]

What about after market oil filters? Don't they make ones that don't allow the oil to drain back? I always kept my trucks stock, but I seem recall reading something in one of the threads about after market (spin on) oil filters. I hope I am not mistaken this for one of the M44 series threads. Maybe someone else knows more...