Talk to me about oil pressure

[GulfSeven]

My 310R maintains 4 bar when driving, but falls to 2 bar when idling, except when warming up when it stays at 4 bar (I assume that's because the idle rpm is held higher by the ECU). From talking to other Caterham owners this is all normal.

I recently bought a 2023 Fiesta ST which, unlike the other cars I've ever owned, has oil pressure (and oil temperature) on the digital dash. Now that car maintains 28 psi (~2 bar) at all times.

So why the difference?

Edited Tuesday at 18:14 by GulfSeven

[Golf Juliet Tango]

As a Crossflow driver I am very familiar & now comfortable with low oil pressure readings when hot & idling. 

[PlastererPete]

Re: oil pressure under warm up is because the oil is thicker afaik. Once it’s warmed up it should idle at 2bar-ish as normal. 
 

As for the Fiesta, it’s a digital dash so maybe the read rate of the signal is slower/smoothed out? Or could be sensor placement in the oil circuit? 

[GulfSeven]

The Fiesta reading flickers between 27 and 28 psi so I don't think it's being smoothed.

Edited Tuesday at 18:09 by GulfSeven

[SM25T]

Perhaps it just shows 28 all the time as a comfort factor. That sounds a bit low for driving under load ?

[StevehS3]

My 310R is exactly the same as yours.
I have had a few modern tin tops with oil pressure gauges (albeit needle gauges) and they have all shown about half the normal pressure at idle with a hot engine.

[Toby S]

Also depends on whether its an electrical or mechanical gauge - mechanical much more accurate and fluctuate more immediately.

K series 1400 Supersport withy mechanical gauge - 65 Psi on start up, blipping to 70 psi, and when hot under load 40-65psi depending on load and 20 psi idling

[PlastererPete]

Could also be down to the type of oil pump itself and also the grade of oil. I know most modern cars use a 0w-20 now for “efficiency” whereas I use a 5w-50 so would potentially stay thicker for longer. 

[Guy Lowe]

4 hours ago, SM25T said:

 

Perhaps it just shows 28 all the time as a comfort factor

 

Like most modern tin top gauges, I have had 6 VW Transporter’s all of which the water temperature gauges start in the “blue” slowly creep up to the middle (normal) position and stay there, even when stuck on the M25 in 30C with both radiator fans going. It’s definitely the “comfort factor”, manufacturers don’t want you to worry 😉

[OldAndrewE]

24 minutes ago, Guy Lowe said:

It’s definitely the “comfort factor”, manufacturers don’t want you to worry 😉

28 psi when pushing the engine hard would not be "comfort factor" for me 😱

[GulfSeven]

I've not looked at it when booting it. Not that I ever boot it of course 😇

Edited Tuesday at 18:15 by GulfSeven

[aerobod - near CYYC]

Our Macan S's V6 along with a lot of other current cars has a variable displacement oil pump. It uses 0w20 oil and typically is 1.0 bar at idle hot or cold and only reaches 3.2 bar at full load and maximum revs. Ford does use variable displacement oil pumps in many current vehicles, but I'm not sure about the Fiesta.

[GulfSeven]

A quick google suggests it's a "two-stage variable displacement oil pump", and that these regulate the pressure across a wide range of engine conditions. I guess that explains it then?

Edited Tuesday at 18:47 by GulfSeven

[supersport_140]

21 hours ago, GulfSeven said:

My 310R maintains 4 bar when driving, but falls to 2 bar when idling, except when warming up when it stays at 4 bar.

My Supersport 140 is exactly the same. I use it as indication the oil is now warm. 

[Jonathan Kay]

1 hour ago, aerobod - near CYYC said:

Our Macan S's V6 along with a lot of other current cars has a variable displacement oil pump. It uses 0w20 oil and typically is 1.0 bar at idle hot or cold and only reaches 3.2 bar at full load and maximum revs. Ford does use variable displacement oil pumps in many current vehicles, but I'm not sure about the Fiesta.

27 minutes ago, GulfSeven said:

A quick google suggests it's a "two-stage variable displacement oil pump", and that these regulate the pressure across a wide range of engine conditions. I guess that explains it then?

Thanks, both. It sounded as if there must be some sort of control system but I had no idea what it was.

Jonathan

[GulfSeven]

I've actually just been out in it to take my son to cubs. I paid close attention this time, and it does go up to 55psi when pulling away from a junction, but quickly returns to 28psi. Pretty neat system. I've learned something from this thread 

Edited Tuesday at 18:13 by GulfSeven

[GulfSeven]

1 hour ago, supersport_140 said:

My Supersport 140 is exactly the same. I use it as indication the oil is now warm. 

It's interesting you say that. As I said in my original post, my Fiesta ST also displays oil temperature (in addition to water temperature). It's amazing how long it takes for the oil temperature to get up to the water temperature after a cold start. I've not timed it in the Caterham, but I'm pretty sure the oil pressure falls to 2 bar when idling in much less time.

[StevehS3]

Presumably the Sigma’s oil/coolant heat exchanger helps the oil warmup to some extent. 

[BigCol]

13 hours ago, StevehS3 said:

Presumably the Sigma’s oil/coolant heat exchanger helps the oil warmup to some extent. 

Such a thing is additional which was highly-recommended by Stuart Creswell.  (I have one as a result and it works well!)

[jbcollier]

Friend bought a brand new truck with a big block engine back in the 70s (454 ci/7.5L).  Oil pressure was 10 psi on the gauge and confirmed by the shop.  He complained.  Dealer said it was fine.  He ran it for years.  It was fine.