Engine oil pressure drops when hot

[FotonOwner]

Hi all,
My Foton FT254 engine oil pressure drops from 0.4 MPa on start up to 0.2 or less when hot (half and hour or so). The oil light comes on when the pressure gets down to 0.2 MPa. The engine is reasonably new changing the oil and filter has had no effect.
Does anyone have any ideas on how to narrow down the possibilities?

 

[PILOON]

When oil gets hot it gets thinner.
When thinner the pressure drops.
Bad news is that generally low oil pressure when hot suggests bearings are in poor condition.

All that being said, I'd first want to get accurate oil pressure readings as it is very possible that the gauge or sender is actually reading falsely.
Can you get and install a manual gauge?, usually the pressure switch is threaded into a 1/8 or 1/4 NPT hole in your engine block and you'd replace with the manual gauge.

You say 'reasonably new', I'd assume in the 500 hr or less range. If that is the case and you don't abuse the engine, then my first approach would be to suspect gauge and or sender unit. ( a bit of crud or corrosion could send the unit out of whack)

Assuming, naturally, that you are using proper recommended oil weights for the climate.
(if, for example, you have 0-40 wt oil and it is +50deg outside, for sure after 30-40 mins of hard work the oil will be hot and thin and show low pressures).

My guess is GUAGE and/or SENDER.

Good luck!

 

[Bob Rooks]

My guess is that it's oil or bearing clearance related. Could also be a bad PRV at the oil pump.

 

[SPYDERLK]

Is the light coming on only at low idle? 200,000 Pascals is around 29psi. I would expect oil lights to come on at 10psi or less. Are you using 15W-40 oil or 10-30?
larry

 

[greg_g]

On these engines, 0.4 right after a cold start is about normal. Hot oil at 0.2 at working speeds is acceptable. Hot oil pressure at idle isn't usually an issue in these engines unless/until it drops below 0.04 (~6psi). But that assumes also that your idle speed isn't set too low, and that nobody's fooled with the pressure adjust on the filter housing (if so equipped).

If you use a 30W oil, it should be diesel-rated (API rating starts with a C). But 15W40 typically generates better oil pressure.

//greg//

 

[TTTTTT]

I would also check at the filter head bracket there may be adjustment screw and lock nut as mine has. At first mine was sky high, after adjustment ,I adjusted it into a normal operating range after warming up. Not sure if all have it though.

Dave

 

[FotonOwner]

When oil gets hot it gets thinner.
When thinner the pressure drops.
Bad news is that generally low oil pressure when hot suggests bearings are in poor condition.

All that being said, I'd first want to get accurate oil pressure readings as it is very possible that the gauge or sender is actually reading falsely.
Can you get and install a manual gauge?, usually the pressure switch is threaded into a 1/8 or 1/4 NPT hole in your engine block and you'd replace with the manual gauge.

You say 'reasonably new', I'd assume in the 500 hr or less range. If that is the case and you don't abuse the engine, then my first approach would be to suspect gauge and or sender unit. ( a bit of crud or corrosion could send the unit out of whack)

Assuming, naturally, that you are using proper recommended oil weights for the climate.
(if, for example, you have 0-40 wt oil and it is +50deg outside, for sure after 30-40 mins of hard work the oil will be hot and thin and show low pressures).

My guess is GUAGE and/or SENDER.

Good luck!

Thank you for the response, yes there are not too many hours on the machine I would say less than 500 and it seems to have plenty of power.

The weather has been remarkably mild here around 20C, so would not expect it to overheat.
The gauge seems to agree with the mug light. When the gauge gets down to 0.2 or perhaps less the mug light comes on. So I am inclined to accept the reading.
I would say it comes on at idle but the pressure is much lower than at start even with revs.

The engine seems overly hot and smoke comes out of the oil breather.

I was told it could be due to loss of pressure due to dirty oil even though the oil was almost new. So I changed from 20W60 to 5W30 (very expensive gold plated diesel oil) - no difference.

I have read comments about big end wear, how does that impact the pressure? I expect you would get some oil leaking through the worn bearings - would not have thought that enough to cause that much drop.

 

[greg_g]

The engine seems overly hot and smoke comes out of the oil breather.

Don't you have a breather return line? On some tractors, those vapors get routed straight to the intake manifold and get burned up. On others, they're routed back into the crankcase. On those without a return, visible vapors are not unusual. But on those the breather element traps the oil component, after which gravity permits it to drain back into the valve cover.

And have you ever washed out the breather element? I do mine twice a year.

Seriously though, there's nothing wrong with 0.2 MPa (MegaPascal). Perhaps you don't realize that 0.1 MPa = 14.5 psi. So you're talking 29 psi on a hot engine. Using 15W40, both mine - once at operating temperature - stay consistently between 0.2 and 0.3 - at working RPMs. under load. They may peak out between 0.4 and 0.45 right after a cold start, and dip to 0.07 or so at hot idle. But I consider all that to be perfectly acceptable.

//greg//

 

[SPYDERLK]

Is the light coming on only at low idle? 200,000 Pascals is around 29psi. I would expect oil lights to come on at 10psi or less. Are you using 15W-40 oil or 10-30?
larry

On these engines, 0.4 right after a cold start is about normal. Hot oil at 0.2 at working speeds is acceptable. Hot oil pressure at idle isn't usually an issue in these engines unless/until it drops below 0.04 (~6psi). But that assumes also that your idle speed isn't set too low, and that nobody's fooled with the pressure adjust on the filter housing (if so equipped).

If you use a 30W oil, it should be diesel-rated (API rating starts with a C). But 15W40 typically generates better oil pressure.

//greg//

Don't you have a breather return line? On some tractors, those vapors get routed straight to the intake manifold and get burned up. On others, they're routed back into the crankcase. On those without a return, visible vapors are not unusual. But on those the breather element traps the oil component, after which gravity permits it to drain back into the valve cover.

And have you ever washed out the breather element? I do mine twice a year.

Seriously though, there's nothing wrong with 0.2 MPa (MegaPascal). Perhaps you don't realize that 0.1 MPa = 14.5 psi. So you're talking 29 psi on a hot engine. Using 15W40, both mine - once at operating temperature - stay consistently between 0.2 and 0.3 - at working RPMs. under load. They may peak out between 0.4 and 0.45 right after a cold start, and dip to 0.07 or so at hot idle. But I consider all that to be perfectly acceptable.

//greg//

Weve been saying this. OP should specifically address these comments.
larry

 

[FotonOwner]

Don't you have a breather return line? On some tractors, those vapors get routed straight to the intake manifold and get burned up. On others, they're routed back into the crankcase. On those without a return, visible vapors are not unusual. But on those the breather element traps the oil component, after which gravity permits it to drain back into the valve cover.

And have you ever washed out the breather element? I do mine twice a year.

Seriously though, there's nothing wrong with 0.2 MPa (MegaPascal). Perhaps you don't realize that 0.1 MPa = 14.5 psi. So you're talking 29 psi on a hot engine. Using 15W40, both mine - once at operating temperature - stay consistently between 0.2 and 0.3 - at working RPMs. under load. They may peak out between 0.4 and 0.45 right after a cold start, and dip to 0.07 or so at hot idle. But I consider all that to be perfectly acceptable.

//greg//

Greg,
The breather is a cup arrangement with that steel element.
I never seemed to have the problem before I had the machine serviced. Never had the light come on but didn't notice what the pressure was.
I noticed that they had overfilled the oil which was way over the top mark. Then oil was dripping out of the breather on to the starter motor. I put the smoke down to it being overfilled and excess venting out.
But now I have it at the correct level and still have problems.

I will try cleaning out the breather element.

Do you think you can get problems from overfilling the oil?