low oil pressure reading - intermittent

[Corban]

These little buggers were blocking the valve from returning to closed!

Anyone recognize what they are and where they come from?

Very brittle, could be plastic or rubber, not soft but I don't know what happens if rubber gets soaked in Castrol Edge for some time, might be hard and brittle. Now I fear my entire oil system might be polluted with this stuff or it is the sign of something worse.

[MrDangerUS]

OIL PUMP /LOW PRESSURE SYNDROME

 

• > Is there a drawing in the service notes or parts list
  > > that shows the relief valve?
  >
  > No, not in a Lotus manual, to my knowledge. The pressure relief
  > valve wasn't a normal maintenance item (not rebuildable, buy new
  > replacement), and as such, wasn't included in the Service Notes.
  >
  > I've got a Jensen-Healey Parts Manual that shows the relief valve
  > parts in the exploded parts drawing and numbers them 14 thru 18.
  > However, it doesn't identify part 18 in the parts list, and the
  > illustration doesn't clearly show what it is.
  > .............................................. Jensen ... Lotus
  > 14 retainer – spring ......... 1 ... 93539 ... B907E0372Z
  > 15 spring – relief valve ..... 1 ... 93540 ... B907E0135Z
  > 16 plunger – relief valve ... 1 ... 93541 ... A907E0275Z
  > 17 sleeve – relief valve ..... 1 ... 93542 ... A907E0199Z
  >
  > I called a Jensen-Healey vendor yesterday (Delta Motorsports), and
  > was told those parts haven't been available since J-H went out of
  > business in the mid-70s... Lotus doesn't provide them.
  >
  > I've also got a partial scan of a Lotus cross-section assembly
  > drawing of the pump, but the resolution is so poor that the details
  > really can't be made out. The Lotus part numbers are there for the
  > relief valve bits, but that won't do any good since those parts
  > haven't been sold by Lotus in decades.
  >
  > Notes on the drawing from Brian Angus (barely legible):
  > Pump Body ....................................... A907E0443Y
  > Pressure Relief Valve Components:
  > .......... Vendor Number ............ Lotus Part Number
  > Insert ...... 30540 ............................... A907E1320
  > Sleeve .... 30839 ................................ A907E1321
  > Plunger ... ?7?58 (57858 / 57258 ?) ... A907E1322
  > Spring ..... 30536 ............................... A907E1323
  > O-Ring ... 550-43 (?) ......................... A907E6099 (?)
  > Cap ........ 30535 ................................ A907E1324
  >
  > Note that the Lotus part numbers above don't match those in the
  > Jensen-Healey parts manual, so some design change took place.
  >
  > Another picture shows a groove machined around the hole into which
  > the distributor/ charge cooler pump fits, and says the groove is the
  > ID mark for that model pump. To me, that implies that there were
  > multiple iterations of the pump, but I don't know what the detail
  > differences were.
  >
  > Oil Pump Housings
  > A907E0443Y Jensen-Healey Oil Pump Body Assembly
  > D907E-803W Lotus Elite-Eclat Parts Manual, 1974-80 - 907
  > E907E-803W Lotus Elite-Eclat Parts Manual, 1974-80 - 912 Sup.
  > E907E-803W Lotus Esprit S1-S2 Parts Manual, 1976-80
  > E907E0443F Fed Lotus Esprit Turbo & Esprit S3, 1980-87
  > C907E0443F Euro Lotus Esprit Turbo & Esprit S3, 1980-87
  > E907E0443F Euro Lotus Excel, 1982-89
  > E907E-803W Euro Lotus Esprit Parts Manual, 1988-92
  > E907E-803W Lotus Esprit SE, S4, S4s Parts Manual, 1993-96
  >
  > Note that the scan of the Lotus drawing mentions pump housing
  > A907E0443Y (Jensen-Healey), which doesn't appear in any of the Lotus
  > manuals I have. However, a note on the drawing says the Modified
  > Relief Valve is applicable to 907 and 911 engines, but it doesn't
  > state what the modification was.
  >
  > Brian Angus sent the pump drawing scan to me shortly before he
  > retired, and said it was the only drawing he could find of the oil
  > pump. At the time, the engine drawings were off to a service
  > provider to be scanned into electronic documents. They didn't
  > return to Lotus before Brian retired, or he would have sent more
  > details. Now, no one has replaced Brian's function and no one at
  > Lotus is as helpful to owners as Brian was. We lost a great
  > resource when he retired.
  >
  > Regards,
  > Tim Engel

[ragingfool35]

could be bits of the form-n-place gasket material used everywhere on the 910.

the original stuff was quite hard when i disassembled my engine for rebuild

[Jacques]

Very interesting read. I'll keep an eye on this.

 

Kind regards,

Jacques.

[top-plumber]

As mentioned probably the sealer. if the whole system was contaminated i suspect you would find evidence of this in the filter and when drained down.

Has the pressure relief valve relocated on its seat?

Probabaly prudent to change oil and filter to check for the bits you found.

[Corban]

The oil pressure was a real thriller...
cleaned the pressure valve from all the little black stuff. Put it all together, new filter, new oil and the old pressure sensor (as it seemed to be working just fine). Disconnected the spark plug leads and cranked it a few times to prime the system. Connected the leads and started it up. Still no pressure on the gauge and light wouldn't go out above 1600 rpm. Not a happy moment. Made a diagram of the system, checking what could fail. Pick up tube from sump loose? Woodruf keys on auxillary shaft? Something blocking pipes to oil coolers? Pressure sender? Finally decided to disconnect oil feed to turbo (easiest and far back in the system). Put it in a plastic bag and cranked it over, nothing at first but after 30 sec, oil started to come out in force :-).
Indicating that the pump was working (that was a sigh of relief). Loosened a hose to the chargecoller and cranked again and there was water pumping. This indicated a faulty sender but at least gave me the guts to run the engine for a while. Noticed the gauge flipping to max pressure when reaching 1600 rpm. Hmmm.... switched the cables on the sender and everyting seem to be working just fine. The connections are of different width to avoid this but when I tested another sender I had to move the connectors from the old one and accidently put them back the wrong way.

[top-plumber]

So where do we stand with the results. Couldn't have been the terminals in the first instance so what conclusions have you drawn?

Was it the debris in the pressure relief valve?

 

Wayne

[Corban]

Yes, summing it all up, the only "actual" fault was the debris in the pressure relief valve. If I had dared to give it more than 2000 rpm when the light went on, pressure might have washed them away into the filter, but that is a hard thing to do...

All other stuff is just links in the chain of events that came from trying to find out what the problem was.

But aside from a few pints of blood, oil and coolant, the cost was only about 20+ hours of labor
Well, it's all part of owning a 25 year old supercar.

[Techspy]

Sorry to resurrect an old topic but I have been having similar issues. Long story short; For the 10 years I have owned my 94 S4 it always shows very low oil pressure while warm at idle. All the way to the bottom of the red. I had the oil pump replaced early on and have even had a rebuild of the engine with another pump replacement (lost timing belt) and it still shows the same. I have replaced the gauge and sender. Same thing. I previously tried to get ohm readings of 3 different senders that I have and they all showed different readings. So, either I have bad wiring somewhere or the gauge and/or sender are out of calibration. FYI, when starting up cold, I get good readings. As it gets warmer it starts to drop. As long as I have RPMs it shows around the 2nd white line. What is really strange is that when I give it a bit of throttle, it will dip a little then recover. When I let off the throttle it will climb a bit and recover. Oh, and have always used 15w 50 Mobile one. Now previously researching this it was pointed out that flow and pressure are 2 different things and having good flow may not show up as high oil pressure.

Now on to the questions;

- Where is the best place (within reason) to connect a mechanical gauge? I have seen people connect to the turbo oil line but is that going to give an accurate reading? I plan to permanently install one somewhere on the engine.

- Does anyone know what the operational ohm of the gauge is supposed to be? After I verify the actual pressure with the mechanical gauge, I plan to put a potentiometer or some resistors inline between the gauge and sender so I can adjust it to read what the mechanical gauge is reading.

Thanks

[Richard123]

John,

 

I put a pressure gauge just before the turbo, but took it off after I verified the readings.  The turbo is last in line, so if you have pressure there, you'll have more everywhere else!  

 

My gauge is in the red at warm idle, but the red area is 0 - 14.5 psi, and according to Lotus the engine needs very little oil pressure (someone will chime in with the exact amount, but IIRC its only a couple psi).  It was a poor idea to use that gauge.  A needle in the red just produces worry (which is why I had to check it out with a mechanical gauge).  They should have used a pressure switch and resistor and had the needle sit at half all the time like my Ford did, lol.         

[Techspy]

Thanks for the info. I will mount it to the turbo and then try to calibrate the dash gauge. Do you recall what size fittings was needed at the turbo connection?

[ragingfool35]

mine used to do same thing until i replaced the chargecooler o-ring with one with a slightly larger cross section diameter.  now it never drops into red at idle and temp.  Just like the IAC, a worn o-ring there will allow air to pass. Get an o-ring kit and give it a try.

[Techspy]

Thanks for the info but I am running an electric chargecooler pump. I have the blanking plug in place of the original.

[Richard123]

21 hours ago, Techspy said:

Thanks for the info. I will mount it to the turbo and then try to calibrate the dash gauge. Do you recall what size fittings was needed at the turbo connection?

Sorry, my memory is horrible.  I know it was metric and that the guy at the local speed shop had lots in stock, so it isn't oddball.

 

Someone will chime in hopefully with the proper spec.

 

My gauge turned out to be almost spot on.  High side of red was 15 psi, with every mark on the gauge adding 15 psi more.  

[ragingfool35]

23 hours ago, Techspy said:

Thanks for the info but I am running an electric chargecooler pump. I have the blanking plug in place of the original.

which still uses an o-ring.  The full story is the oil pressure got worse, as in it would peg bottom of gage unless RPMs were above 2000, just after installing my blanking plug.  The o-ring that came with the plug was just a tad too small in cross section, though i could not tell by feel of installing the plug.  Just for kicks i installed one with a larger cross section and it was much snugger when fitting the plug into the hole (even well oiled, it took a very firm push).  And voila! no more low pressure at idle, not even in the red anymore!  i would never have guessed such a small change would have such a big effect.

i dont even have the RPM relay connected anymore, dont need it

[Techspy]

Ah ok. Good info. I will check it out.

[s4simon]

Lotus made a bit of a mess with this.  The fitted transmitter range is different to the Receiver display range.  I think the transmitter was 0-5 and the receiver (gauge dial) was 0-7.  Hence it will always read under. Mine has always read low once warm at idle.  The other problem is that Lotus states that the minimum pressure allowable is like 0.6 bar whereas the redline on the dial is 1 bar.  So there are lots of issues that Lotus have presented to us.

[andydclements]

Maybe Lotus applied an immense amount of thought to this and deliberately set out to confuse us, or maybe not and it's a happy coincidence.

If (BIG if) the gauge under-reads consistently proportional to the actual pressure then maybe the numbers of the gauge are more like a volume setting than a calibrated measurement. By this, I mean that if the gauge indicates a pressure that's half way it isn't 3.5Bar but it is twice what the pressure would be when the gauge is at 1.75Bar.  

The 0.6 minimum, Vs  redline thing isn't too bad (with that same if statement), 0.6bar, would be 0.6/5 (aka 12%) of the transmitter's output potential range, 12% of the gauge's range would be  7x0.12 which is 0.84Bar, so not 1Bar but also not immensely different to 1Bar (the redline value). So, perhaps Lotus couldn't find a suitably priced gauge that fitted in with the dash scheme and had a redline at 0.6Bar, and opted for away to approximate it.

[Escape]

I saw a 0-5bar oil pressure gauge in an Esprit once, IIRC it was a 89 N/A. Both my SE's ('89 and '90) have a 0-7bar gauge.

The partslist for '88 to '92 shows both gauges, depending on VIN/engine n°, and 2 corresponding oil pressure sensors, one with a range of 0-7bar and the other 0-10bar.

[ragingfool35]

i recently rebuilt my engine and installed VDO sender and matching gage and get the following, units in PSI.  i wonder if my results are typical?  this of course with the o-ring installed many years ago that greatly improved idle oil pressure reading on stock gage/sender.  It would seem that a fresh engine should not be near the .6 bar minimum.

oil pressure	idle	3500 rpm
cold	60	60	20w-50
hot	40	60	10w-40
hot	30	60	10w-40	6k miles

 

 

[Techspy]

I think that proves it isn't an actual oil pressure problem. I had my engine rebuilt and the low pressure readings were exactly the same.

Can someone explain how the O Ring on the chargecooler effect the pressure? I mean, it is there to prevent oil from leaking out of the engine. If it isn't leaking, it is doing ti job. What doe having a larger O Ring have to do with pressure readings?

[ragingfool35]

the aux shaft drives the oil pump and the chargecooler pump.  the chargecooler pump appears to be located on the intake side of the oil pump, right at the pump itself.  it seems that if this is not sealed very well against the vacuum the oil pump generates to pull oil from the sump (like a milkshake thru a straw), that it pulls air thru the chargecooler pump housing hole instead. its easy to test: remove the oring and observe oil pressure behavior.  when the engine stops, some oil will then leak by the absent o-ring.  i would do it and post results, but i dont have a plug there anymore that is easy to remove and install.  if you have a few minutes, it would certainly be worth it.  AFAIK i'm the only one to install a larger o-ring and note the result

in all seriousness, i was shocked at the increase in oil pressure at idle just from a better seal

[Techspy]

Ahh, interesting. This may be why I see an increase in pressure after giving throttle and then letting off the throttle. I will be replacing the O ring in the near future and will report back. Probably in a couple months after a trip overseas.

Edited August 21, 2016 by Techspy

[ragingfool35]

@techspy did you ever try the oring?

[Techspy]

Not yet. I would have already if I know what size O ring to get. I just haven't motivated myself enough to remove the blank and O ring and drive around to try to find one a bit thicker.