Thread: 2.25 oil pressure at idle

Low oil pressure when idling can point to:-

Worn pump
Pressure relief valve not seating properly,
worn bearings.
Excessively low idle speed - should be around 550rpm (which is slow by modern standards
cracked pipe on pump suction or blocked screen.
Major oil dilution - but if you have this I expect other symptoms

My feeling is that it is not really an issue as long as the pressure remains normal at anything over a fast idle (1000rpm) with the oil hot.

Fair enough - thanks John. The warm/hot idle is a little slower than I think it should be, hopefully that's all it is.

I know it's not oil dilution (new oil) or worn bearings (engine rebuilt a couple of years ago), so if it's unlikely a problem I'll wait until I next do an oil change and give the oil pump a good inspection.

One thing to remember is 20 w 50 oil is thinner when cold to allow the oil to circulate quickly through the engine at startup and then gets thicker as the engine gets up to normal operating temperature. So when you start in the morning it is 20 on the viscous scale and when it is at operating temperature it should be 50 on the viscous scale. Having said that as John says your idle may be low or there could be and issue with the oil pump ie. relief valve spring worn gears etc. Perhaps the oil pickup has a leak on the piping or a plugged strainer, i would monitor the system and set the idle speed as per the manual. If the oil light keeps flickering at normal revolutions and there are no other external issues it may be prudent to remove the sump and inspect the oil pump and it piping.
Gippy

Thanks for the input guys. I have an update on this - after some travel, I was finally able to take it for a run today. I measured the stone-cold idle speed at 600rpm, and after a little bit of highway running got it up to 60°C (much cooler weather than two weeks ago). I pulled into the garage and the thing was idling at 320rpm! I realised it would slow when warm but had no idea it would almost halve.

I've adjusted it back up to 520RPM (close enough to the 500rpm in the book for my tastes), next weekend with really hot weather and some spare time I'll try to get the engine temperature up to 90°C again and see if the light comes back on, and if so, what speed it's idling. But I suspect this was my issue.

Cheers,
- Will

G'day All,

The important thing is what is happening at 2,000 rpm. With the oil hot you should have around 60 PSI with a healthy engine.

The sump capacity for a 4 cylinder engine is 6 Litres so always have it at full mark, meaning more oil means cooler sump temperature. With an ambient temperature of around 30 degs the oil temperature is around 145 degs F in Sydney traffic.

The coolant temperature at 30 degs ambient can be between 168 to 172 degs F in Sydney traffic.

Chris

My series 111 2.25 diesel takes 6 litres of oil plus .85 litres extra for the filter.
I find as my oil level drops owing to some being burnt by the engine once it goes below half way on the dipstick the oil pressure light will be slow to go out. Once topped up it is fine. I use 15w-40 mineral oil. The workshop manual and handbook state to change the oil and filter every 6,000 miles or 10,000 kms but I do it at 3,000 miles or less if the yearly change comes before the miles.

G'day All,

Just a correction due to typo. At 2,000 RPM with engine hot, oil pressure should be around 50 PSI for a healthy engine.

Chris

Originally Posted by Gippslander

One thing to remember is 20 w 50 oil is thinner when cold to allow the oil to circulate quickly through the engine at startup and then gets thicker as the engine gets up to normal operating temperature.

That is not true. It always becomes thinner as it heats up. Multi weight oil just don't change as much as straight weight oils.

20W - Tells you the temperature at which it becomes pumpable (-20 C for a 20W)
50 - Tells you the viscosity at 100 C (16.3 to 21.9 cSt)