low oil pressure reading - intermittent

[ragingfool35]

wish i knew what size, i had an assortment on hand so it was easy.

[Techspy]

Finally changed the o ring. It was a tight fit, took a lot of effort to get the blanking plug back in place with the larger O ring. Didn't make a difference. Still have the low reading at temp.

[jcslocum]

I'm fighting a similar problem on my '84. 

 

 

I have a new oil pump to install and check all clearances. It will take a few weeks to get there as I'm headed to IOM for the TT races.

When I have it out I will pay close attention to the OD of the Annulus (outer part) to the housing if the pump looks good internally. This is what the oil pump looks like and how it works. Clearances must be spot on for it to function properly. I'm hoping this is what will solve my problem. If the housing clearance is off, i'm not sure how that will be fixed. Maybe weld up and remachine

 

Edited May 26, 2017 by jcslocum

[ragingfool35]

On 5/25/2017 at 14:54, Techspy said:

Finally changed the o ring. It was a tight fit, took a lot of effort to get the blanking plug back in place with the larger O ring. Didn't make a difference. Still have the low reading at temp.

thanks for testing.  odd that it worked on my car.

[swindon_alan]

Other events have been a priority but seeing this I will post it up now.

I have had a similar problem with oil pressure readings on the gauge of my V8 since acquisition (ok, it's a different engine but the sender and the 7 bar dial are the same as the S4/S4). It has always read very low, just above the 1 bar red area even when cold. In fact in France last year I stopped the car as the reading was so bad I thought that it had lost all of the oil. It hadn't.

The minimum oil pressure specs from the service manual are:

Also, the V8 oil pressure warning light is set to come on under 20psi (1.4 bar, the minimum hot idle pressure), which it never has while the engine is running. I have always concluded that the calibration is pants and in fact the pressure is fine and pretty much ignored the gauge.

However, here's the rub. I performed my first oil and filter change on the car the week before last. The only one before this in my ownership was done by the repairer after the accident - I didn't have the car long enough before then to notice what the oil pressure was - and I fitted a nice new shiny K&N filter:

I was astonished to see that after the service the oil pressure had shot way up on the gauge, so much so that I thought I must have overfilled it. Nope, right at the top of the dipstick when cold. So now after some good runs I am consistently reading at over 3 bar (40 psi) at 2,500 rpm! Bearing in mind that nothing has been changed on the sender, electrics or gauge I can only surmise that the previous oil filter - a generic unbranded one - was horribly restrictive in some way. Now I'm not complaining, it is very comforting to see that needle nearly half way up the dial and must surely be better for the engine if it is getting better pressure?

Has anybody else tried or experienced this? It might be a fix, @Barrykearley mentioned on Saturday that his gauge hardly reads very much...

[Barrykearley]

It's the 7 bar gauge that's the issue - when mine is hot and on idle it's just over the red - which is 1 bar !!! It's not a great scale

Is there something about lotus filters having a different setup on them ??? I'm sure they were not exactly a normal filter.....

[Escape]

Alan, since I started using the K&N HP-2004 I also noticed the pressure reading was a bit higher. ;-)

[Giniw]

With the exact same new oil? (I mean, not a used one just before you flushed it and a fresh one with the new filter)?

I for one installed a Mann filter but I don't have a real reference since the sender needed a change when I bought the car (https://www.thelotusforums.com/forums/topic/86872-s4s-oil-pressure-caerbon-gauge-or-sender-or-wiring-issue/)

As I quoted there, with unknown oil and a lotus filter it did read almost 4 bars when idling and cold: https://www.thelotusforums.com/forums/topic/86872-s4s-oil-pressure-caerbon-gauge-or-sender-or-wiring-issue/?do=findComment&comment=713444

Edited May 31, 2017 by Giniw

[swindon_alan]

Yes, 6.5 litres of Castrol Edge FST 10W60, same as the previous fill.

Incidentally, thinking about the last couple of trips when warm the oil pressure hasn't gone much above 3.1 bar at any revs (that's the 6,500 rpm minimum), so that is probably the oil pressure relief valve doing its job. Although I can't find any spec on opening pressure. I would assume the four pot is the same?

It does go a bit higher when cold but the service manual says that is to be expected and ok.

[Techspy]

A couple of thoughts/observations.

- I have changed the gauge and tried 2 new (used) sensors. Same issue. I have tested 3 sensors and get different resistance with all 3 :/ I have disconnected the dummy light as it is just too annoying.

- I am pretty sure it is just the calibration between the gauge and sensor.

- I have had this issue since I purchased this car. I have had a complete engine rebuild at which time the oil pump was replaced. Didn't make a difference and the old pump looked fine.

- Oil is probably pretty darn different between now and when this system was designed. Possibly contributing to the issue.

- Just because you have low pressure showing doesn't mean you don't have good flow.

- If you have higher pressure after changing the oil filter, it could be that the filter is more restrictive, causing less flow and more pressure.

- I am considering adding a mechanical gauge somewhere on the engine, possibly on one of the turbo connections. Then install a rheostat between the gauge and sensor and adjust until I have 1 bar showing at idle and in the red when engine off. At least this way the gauge will provide useful info.

- Another option I am considering is installing a pre-lube/supplemental electric pump for extra peace of mind.

Ahhh, Lotus ownership. Such an Unexpected Journey!

[swindon_alan]

13 minutes ago, Techspy said:

- If you have higher pressure after changing the oil filter, it could be that the filter is more restrictive, causing less flow and more pressure.

I think I'm right that the pressure transducer is situated on the main oil gallery so should read the pressure at the point of use (crank, cams, piston spray etc?) If the filter was more restrictive then you would have a lower pressure on the business end?

S4/S4s service manual:

Oil Pressure Gauge
This gauge is calibrated in bar units and registers oil pressure as detected by the sender unit in the oil gallery cover at the rear of the RH side of the
block.

[Giniw]

1 hour ago, Techspy said:

- If you have higher pressure after changing the oil filter, it could be that the filter is more restrictive, causing less flow and more pressure.

I would say that more pressure doesn't mean less flow since I understand that the quantity of oil passing thought the system is driven only by the oil pump. To me, more pressure means that it's more difficult for the oil pump to pump the oil, but that's it.

Just imagine our pump pushing the oil through a big hole (=no restriction to the flow). There would be no measured pressure at all, but the flow would be still there. Then, take the same pump pushing the same hole trough a little hole (=high restriction to the flow). The measured pressure would be high, and the oil would be accelerated a lot to pass the little hole. (same as a garden hose really, the water pressure delivered is constant when it arrives at your home, but the measured pressure in the hose would range to 0 to the town delivered pressure if the hose is closed at the end)

So, to me, the measured pressure depends only on:

• the max pressure the oil pump is able to push: could theoretically decrease if there is a lot of play in the pump I suppose. (as it's driven by a 265+bhp engine, I gather it's quite high )
• the restrictions in the oil circuitry. Mainly the engine bearings: if the tolerances are still low (good engine), the measured pressure will be high since the oil will have a hard time to go through those little gaps. And if the engine is good for a rebuilt, the gaps are bigger, hence the lower measured pressure.

I may be missing something tough.

Edited May 31, 2017 by Giniw

[Techspy]

You may be right. It all comes down to where the more/less restriction is in relation to the sensor etc. In any case, as I understand it, good flow is more important than pressure (up to a point I guess).

And just to reiterate, my oil pressure readings were exactly the same after my engine rebuild from a very skilled and reputable Lotus mechanic. So at least in my situation the issue is very very unlikely to be related to engine/oil pump wear/tolerances.

Edited May 31, 2017 by Techspy

[MrDangerUS]

I also had a low pressure reading at the tick over on my S4S (32K miles). When hot, it was in the red zone.

Front glass (plastic) on 3 original Caerbont  gauges separated /caved in.  PO tried to repair by gluing them, but they failed again.  Use of cyanoacrylate fogged my water gauge.

Got p.. off and have replaced all with metal can VDO gauges and senders w/real glass. Original parts were made of plastic and failed miserably.

In addition, my new turbocharger does not require full oil flow. Triple ball bearings CHRA has an oil restrictor (0.4mm hole) raising oil pressure in the whole system v. effectively. Tick over pressure never been below 20psi hot.