low oil pressure reading - intermittent

[lotus4s]

Blue arrow in the pic. A bit of a pain to get to but easier if you remove the plenum cover. You may need to replace the gasket if you do.

[Richard123]

It was your old post (Lotus4S) that inspired me to get the fittings to actually check the oil pressure!

I've got everything hooked up and am just waiting for a nice day to take the car out and get it all heated up.

Interesting reading about the long trek the oil takes from pump to sump, and how the needle can sit in the red when you have 3 times the required oil pressure.......thank goodness for forums like this where people know a bit about the peculiarities of these cars!

Edited July 11, 2011 by Richard123

[Richard123]

Just to complete my contribution to this thread.....

I finally got a decent day to warm up the car with the gauge attached. The in-car oil pressure gauge was actually quite accurate.

Start up was 5 bar (75 psi at the turbo). Hot idle was 1 bar (edge of red zone in car) and 16 psi at the turbo. 3500 rpm was 3.5 bar and 50 psi at the turbo.

So, overall I am satisfied that the 16 psi I get at a hot idle is sufficient (shop manual calls for at least .35 bar = 5 psi), and the fact that the needle is touching the red zone on the gauge will no longer stress me.

Car has 50,000 kms on it, btw.

[lotus4s]

Good deal.

Glad to hear it tested out fine, most usually do...

Edited July 14, 2011 by lotus4s

[danceswiththewolf]

Hello! I've got a 90 Se with the same problem, Oil light comes on pulling away from lights, for 1-2 seconds maximum. Oil pressure seems fine as soon as engine speed rises, and no warning light at idle. If I am reading everything above correctly the actual fault is the speed relay which should stop the light coming on as the revs rise. Any idea where it is? I've got the workshop manual but it is from the later 92-93 cars, and I can't find anything on my 1990 car.

Thanks

Kenny

[sanj]

I'm sorry, but your problem is low oil pressure. The purpose of the speed relay is to prevent the light from coming on at engine speeds below 1600 rpm, at which oil pressure might be lower than the idiot light sender switching threshold. Lotus obviously did this to avoid scaring customers on hot days. The down side is, you could literally have zero oil pressure, and the idiot light would stay off until you rev over 1600.

Your oil pressure is evidently low enough at speeds slightly over 1600 rpm to (rightly) make the light come on. If you were to bypass the speed relay (which I recommend), the light would actually be on all the time, until your revs reached a high enough level to bring the oil pressure up.

[Richard123]

Hello! I've got a 90 Se with the same problem, Oil light comes on pulling away from lights, for 1-2 seconds maximum. Oil pressure seems fine as soon as engine speed rises, and no warning light at idle. If I am reading everything above correctly the actual fault is the speed relay which should stop the light coming on as the revs rise. Any idea where it is? I've got the workshop manual but it is from the later 92-93 cars, and I can't find anything on my 1990 car.

Thanks

Kenny

I'd also assume your speed sensor is fine.

The light is coming on because at 1600 rpm your oil pressure switch hasn't passed 1.4 bar yet. Now, before you tear the engine down.....the switch may be lazy, the oil filter might be a tad plugged, your oil might be a bit thin, etc. And even if you really don't quite have the 1.4 bar......what are you going to do?

I can get a flicker of the light taking off on a hot day, but all the other oil pressure tests were fine so I'm not going to worry about it. Seems to me that if I need 0.35 bar at idle (and I have 1 bar) then the engine will survive a half second with that 1 bar even when the Lotus engineers wanted 1.4 bar!

See above for rigging up an oil pressure test. Then you will know you don't have a problem!

Edited May 22, 2012 by Richard123

[Rich H]

Yes, check the oil pressure directly.

Never assume it's a gauging problem - prove it's a gauging problem!

[MrDangerUS]

Easy fix:

Check your pump clearances and oil pressure regulator spring rate (replace or add shims). 

There is an outbreak of "low oil pressure disease" all over. Perhaps springs are getting "tired" after 20-25 years?

 

and/or

Go with the heavier viscosity oil, 20w50 or straight SAE50 aviation oil

 

More complex fix:

Add .100" restrictor to the oil line in the head (or deck) to prevent over-oiling the cam area 

 

Worst scenario: your big end shells are on a life support.

Edited July 27, 2014 by MrDangerUS

[eeyoreish]

OK, so I've read this thread and with the reference to 'early' and 'later' cars I'm not completely clear which bits apply to mine, a 1990 Stevens N/A. 

 

I noticed that on cold start up the oil pressure on my car was a bit 'lazy' coming up, i.e the car would start and idle but the pressure gauge wouldn't pop up straight away. The oil warning light would go out but if I blipped the throttle lightly it would sometimes come on again for a split second before going out as the gauge sprung into action...

 

The car is new to me and I've no idea on the age/spec of the oil and filter so decided to change both hoping for an improvement.

 

I've just replaced the oil with Millers Classic Sport 20W/50 semi synthetic and fitted a new (PNM) filter but the same thing still happens.

 

Pressure when running is great and I don't have any problems with the light coming on at tickover or when pulling away as experienced by other people here. 

 

Is something amiss (lazy/blocked oil pump??) or is this 'normal'?

[Mike6]

Neil

 

I would say all is fine with your oil pressure.

[eeyoreish]

Neil

 

I would say all is fine with your oil pressure.

I'm just a bit twitchy about it, which makes me pay even more attention to the light...!!

[mdw]

SOunds about right. The factory recommend Castrol 10/60 (edge?).  I posted a few clips of startup using 2 different filters on a Lotus bits rebuilt engine.  Its alarming but sounds like the rest of us. Mine will also be the same engine as yours so have a search and see if you can find the clips.

[eeyoreish]

SOunds about right. The factory recommend Castrol 10/60 (edge?).  I posted a few clips of startup using 2 different filters on a Lotus bits rebuilt engine.  Its alarming but sounds like the rest of us. Mine will also be the same engine as yours so have a search and see if you can find the clips.

Thanks Malcolm. My handbook and engine sticker both say 20w/50 so that's what I've used.

I'll try and hunt down the clips. TBH as long as it's considered normal I won't worry too much!

[ragingfool35]

i posted several years ago that my chargecooler pump o-ring was slightly undersized, allowing the oil pump to loose prime at idle.  after fitting a very slightly larger o-ring, my pressures have always been 30 psi hot idle, 60 psi 3k rpm and above.

i think Travis posted a similar experience on that thread.

not sure what is there for N/A?  a plug, distributor? probably has an o-ring.

worth a try

[mdw]

Na is just an o ring on the dizzy. Other than that it's the olive on the dip stick tube

[Corban]

OK, this seems to be the right thread.

Today I was driving along and everything was hunky dory (SE MY90). Engine temp. at 83°C, oil temp roughly the same and oil pressure gauge showing normal readings. I stopped for fuel and when I started again, the oil pressure warning light didn't go out and the gauge didn't show any reading at all (needle didn't move). I was in first and had driven 2 meters when I noticed and immediately turned the engine off. After a minute or so I decided that I would restart and give it some revs to see if the needle would move up the scale and the light go out.

Restarted, oil pressure light went out but no movement of the gauge needle. Revved it to 2000 rpm, warning light came on but no motion from the needle. Light went out at idle. I shut it down as quickly as possible. Called a friend and got the car home on a rented trailer. I do not dare start it until I know what is going on here. Oil level is at top mark on dipstick. No visible leaks or puddles under the car. Normally light goes out at once and needle show within normal values even on a hot day with hot engine (but on the low side at idle).

Could the pump fail? In what way if that's the case? Sensors failing? Valves and/or their springs? Could use a list of what to check and in what order (and how). 

[Vanya]

Technically the light should only illuminate at above I think 1600 rpm - this is to indicate that no pressure is building up. Considering your gauge is showing no pressure I'd say you did the right thing. The operation of the light is mentioned in the owner's manual and service notes. I'm actually troubleshooting something similar on my car right now - my oil AND engine warning lamps came on during braking and in corners the other day...

 

Check that neither of the two terminals of the oil pressure sender didn't accidentally come off....You can see these if you look carefully from the top of the engine - the sender is situated right behind the oil filter. I think one is for the light and the other is for the gauge. 

[Corban]

Thanks Vanya, I'll check the connection to the pressure sender. Had a swift look in Service Notes and it is the same thingy for both tell tale light and gauge.Should have been better with two different senders (independent systems). Couldn't find anything about how it is removed. Should I unscrew the hole sender (as if it was one large screw) or are the smaller screws holding it. Parts manual doesn't give much info either. Looking at the oil pump design it doesn't look like much could break down in there.

I will start with the sender for now.

[top-plumber]

On very rare occasions my oil light flashes when pulling away from a standstill when the oil temperature is high. 85-90•

Not sure if it has something to do with the viscosity of the oil at high temps. Although optimum temp is 80•

Pressure at the gauge is higher when the oil is cool.

[top-plumber]

Just checked the manual. Could be the pressure bleed off valve stuck open. It's a spring plunger type. Spring may be weak or stuck. Bleeding pressure off back into the inlet side. Maybe...?

[Corban]

Was thinking along the same lines, that it could be the pressure bled off valve. There were no funny sounds from the engine so I think the pump still rotates as it should. Hopefully it is only some faulty wireing / connections

[top-plumber]

Probably is the sender thou.

[Corban]

Decided to start with the pressure sender. Disconnected the wires. In my case the one towards the front is tell tale and the one to the rear is the gauge. Turned ignition on and gauge went to show max pressure. Connected the gauge to ground and the needle went to zero pressure. The tell tale was harder to check that way as it should light when ignition is on. Measured resistance through the sender to ground, zero on both connections. Turned ignition off and measured resistance over gauge to ground, zero.

Removed the sensor (had to split plenum, remove oil filter, slacken and turn plenum support rod).

If I measure resistance between A and B I get 7.5 ohm

If I do connection A (gauge) to ground on sensor I get 11.3 ohm unloaded

and I fitted an air pump and pushed, the highest reading I managed to get is 52 ohm.

This value changes when changing pressure.

B (tell tale) to ground unloaded 5 ohm and it cuts when pressurized.

So it if these are the correct figures it seems to work.

(picture off the internet, not my car)

[Corban]

Since the sender looks like it is working, I continued to the oil pump. Removed the chargecooler pump and the "lid" to the oil pump housing. Couldn't see anything wrong right away. Took the lid to a better workplace (kitchen) to clean and check. Should the pressure regulating valve be totally closed when not under load? If so I have found a really plausible culprit. I can blow air through the "legs" without a problem.

Mr DangerUS mentions changing the spring or putting some shims in there. This suggests to me that it is possible to take the valve apart. But how does one do this?