losing oil pressure when hot

[alfmech]

hi guys first post here so please be gentle with me

a friend has asked me to try and help with his 1991 elan se, he obtained the car as a non runner due to head gasket failure so had the head sorted and replaced then when it was road tested everything seemed fine untill it was then driven a second time and the oil light came on and the oil pressure gauge dropped to almost zero,
the installation work was rechecked incase of a pinched wire but nothing found

it has had an oil and filter change but still does the same thing, it seems fine when cold then when it is restarted it does the same thing yet if it is left running stationary it is fine and dosnt lose pressure at all even when it is revved, switched off and on it has been left running for over an hour and no fault showed up.
does anyone have any suggestions please?

[esprit888]

As its fine when stationary and hot it sounds like an electrical/ground issue. It is possible that you disturbed the pressure switch connection when working on the head, its located at the rear of the block (see pic) If that's not it then you should first confirm the oil pressure with a mechanical gauge (both cold and hot and on a run) as I am guessing its fine (when the pressure drops on the electrical gauge do you hear the hydraulic lifters clatter?)
Colin

oil pressure switch.pdf

hi guys first post here so please be gentle with me

a friend has asked me to try and help with his 1991 elan se, he obtained the car as a non runner due to head gasket failure so had the head sorted and replaced then when it was road tested everything seemed fine untill it was then driven a second time and the oil light came on and the oil pressure gauge dropped to almost zero,
the installation work was rechecked incase of a pinched wire but nothing found

it has had an oil and filter change but still does the same thing, it seems fine when cold then when it is restarted it does the same thing yet if it is left running stationary it is fine and dosnt lose pressure at all even when it is revved, switched off and on it has been left running for over an hour and no fault showed up.
does anyone have any suggestions please?

[rip]

What about the oil pressure warning light? If the gauge shows zero & the light stays off, this would also suggest an electrical fault.

[nsr250]

Check the oil pickup screen. They get stopped up.

[esprit888]

What about the oil pressure warning light? If the gauge shows zero & the light stays off, this would also suggest an electrical fault.

He does say the pressure drops and the light comes ON , I don't have the wiring diagram but from memory I believe both are wired into the pressure switch ? Also check all of your engine block ground cables as the pressure switch/warning lamp both require a good ground connection form the block, a loose or partially broken connection would give you the symptoms you describe.

[tigerdog]

Good observations, all. if pressure is dropping that much, the engine sound should change audibly (rod knock, clicking lifters, etc.) I'd look for a second opinion in the form of a different sender and/or known good mechanical gauge. I certainly wouldn't wait to check it out, though. FWIW, the wrong oil will cause this, too. I had issues with 0W40 full synthetic thinning too much when hot and removed it immediately.

[alfmech]

thanks for the suggestions, i am trying to get access to the manuals section so i can have a nose through and get an idea of layout and wiring but as yet i have no password to view them. i will try to find a mechanical gauge to test the pressure and if i can get the diring diagrams i will try and track the wiring through to check connections and earths,

i did consider oil but wouldnt that also cause the issue with oil pressure and light also? it behaved ok for over an hour at tickover without being driven

[maz_r]

Hi there,

The wiring diagrams are on the WikiLEC here.

Not the full electrical manual, but may get you started...

Martin.

[rip]

He does say the pressure drops and the light comes ON

Oops. Missed that

[alfmech]

latest update:-
checked wiring to sender unit and after much scraping of arms and knuckles was able to test it and all appears fine.

checked with owner who said oil put in it was fully synthetic 5w30. local factors seem to agree that it should have 10w60 so have changed oil and filter with reccomended grade

so far unfortunatly i have been unable to find another gauge to test it with either electrical or mechanical

after cranking to get oil pressure i started the beast up and the gauge was a little hesitant in reaching the middle of the gauge but seemed stable when it did (hooray i thought its fixed!) wrong!

as the engine warmed up the gauge gradually dropped to the point that if it was revved a little the oil light came on and the gauge almost hit zero

i note there is no noisy tappet sound at this point or grumbling indicating no pressure but the gauge remains at almost zero and the light flickers when revs are raised

what am i missing? could the pump strainer actually cause these symptoms?

[esprit888]

latest update:-
checked wiring to sender unit and after much scraping of arms and knuckles was able to test it and all appears fine.

checked with owner who said oil put in it was fully synthetic 5w30. local factors seem to agree that it should have 10w60 so have changed oil and filter with reccomended grade

so far unfortunatly i have been unable to find another gauge to test it with either electrical or mechanical

after cranking to get oil pressure i started the beast up and the gauge was a little hesitant in reaching the middle of the gauge but seemed stable when it did (hooray i thought its fixed!) wrong!

as the engine warmed up the gauge gradually dropped to the point that if it was revved a little the oil light came on and the gauge almost hit zero

i note there is no noisy tappet sound at this point or grumbling indicating no pressure but the gauge remains at almost zero and the light flickers when revs are raised

what am i missing? could the pump strainer actually cause these symptoms?

This is different from what you reported on your first post when you mentioned ' it seems fine when cold then when it is restarted it does the same thing yet if it is left running stationary it is fine and doesn't lose pressure at all even when it is revved' IN the first post you indicated it was only once driving? You will never know until you use an alternative method of confirming the pressure gauge (preferably mechanical, gauges can be purchased for under $30) Its all total guesswork until you are sure that the pressure is low (which from the lack of valve clatter does not seem to be the case as owners have reported valve clatter simply from using a lighter oil) Its a Bitch to get a hose and gauge on there but dropping the pan to see if the strainer is plugged is a lot harder! Plus low pressure would be indicated whether hot or cold if the strainer was plugged.

[nsr250]

I've had it happen on 2 different cars with this engine. Everything is fine at idle and when cold. It's only when the engine warms up and revs kept up that the oil pressure drops. Both of mine were caused by blockage in the oil pickup screen. And it's not difficult to check, just a few hours work.

[norman lovie]

A typical sound with a blocked strainer is a high pitched "whine" as the pump cavitates
your symptom's of good readings at low rpm - = gauge has a signal - then lost at high rpm = potential cavitating pump
Fine until you rev it - then you can't get the signal back = pump is air-locked = need time for oil to recharge into the pump circuit
repeated good signals at cold / low rpm and repeated loss of signal at hot / high rpm = gauge is getting a signal - maybe something quirky going on - but 1st thoughts are oil not gauge

forsure check the sensor / wiring etc.. - but don't drive it until checked - and i'd drop the sump and check the strainer - not waisted effort - something you should consider as a service item these day's

[saska]

latest update:-
checked wiring to sender unit and after much scraping of arms and knuckles was able to test it and all appears fine.
checked with owner who said oil put in it was fully synthetic 5w30. local factors seem to agree that it should have 10w60 so have changed oil and filter with reccomended grade
so far unfortunatly i have been unable to find another gauge to test it with either electrical or mechanical
after cranking to get oil pressure i started the beast up and the gauge was a little hesitant in reaching the middle of the gauge but seemed stable when it did (hooray i thought its fixed!) wrong!
as the engine warmed up the gauge gradually dropped to the point that if it was revved a little the oil light came on and the gauge almost hit zero
i note there is no noisy tappet sound at this point or grumbling indicating no pressure but the gauge remains at almost zero and the light flickers when revs are raised
what am i missing? could the pump strainer actually cause these symptoms?

Whilst it is possible the pump strainer is causing the problem, check the easy things first.
1. Are you certain the sender is wired the right way around ? Brown/White wire to WK terminal and White/Brown wire to G terminal.
Easiest way to check this is with a digital camera with the flash open. Take half a dozen in the general direction of the oil pressure switch and whack them onto a computer to get full resolution. You haven't a cat in hells chance of eyeballing it directly when the the engine is in the car and mirrors can be confusing.


2. Since the combined oil pressure sender/warning light switch is only grounded via the engine block/head, check the earth connection of the engine to chassis. Most important since the head has been off. Main earth connection braid is beneath the engine hoist at rear of head, engine end nearest the timing belt. Check the braided earth strap is clean, good & tight at both ends.

[RayD]

Nice to see you back Tony

Ray

[alfmech]

good news, i think i found the problem

bad news engine needs a rebuild

checked everything yet again, found an electronic gauge to try with the same result.
i bit the bullet and removed the sump, i was quite hopeful when i saw the crud in the strainer until closer inspection showed it was mostly made of chunks of white metal.

big ends shot and at least one gudgeon pin that i can see i cannot believe it sounded so quiet in such poor condition
crank is scored,
masses of end float in the crank (about 2-3mm)
i havent bothered removing the mains yet to see how bad they are

i broke the news to the owner and he now believes we should look for another engine and stop flogging this dead horse,

is there anyone in the UK selling a complete enging in known good order and if so what sort of money?

A BIG thankyou to all of you for your tips and advise trying to help me get her running properly

[Fredjohn]

Sorry to hear of your worsened problem.

Check out ebay, there are a couple on there which are from well known Elan/Porsche/etc breakers Douglas Valley Breakers (DVB) aka stevestrange007.
You may be lucky

[theelanman]

Nice to see you back Tony

Ray

welcome back saska...

[HJ2]

Contact Peter D.

It is very good possible he has a spare engine that he is willing to sell...

[alfmech]

peter who?