Erratic to no-existent oil pressure - diadnostic help wanted

[Roy Gillett]

What I have always found this forum fantastic at is diagnosing seemingly unfathomable problems. I hope you all can help this time. This is likely to be a bit long as early investigations will be described!

While on the 3 Castles Welsh Trial last week I started having oil pressure problems. After the last thrash of a very hot Thursday I noticed that my oil pressure (high capacity, high pressure pump which usually runs at at least 30psi at tick over and against the 60psi stop over 2000rpm) was almost zero at tick-over and rising to only 30psi from 3000rpm onwards. Everything was VERY hot so I let the car cool down (overnight) and started it up next morning to find no oil pressure at all, not a flicker on the gauge. Disconnected oil capilary on the back of the gauge, no oil emerged with engine running so its doesn't appear to be a gauge fault.

At the rally support garage I loosened off the oil filter cartridge, started engine, - no leakage therefore no oil being pumped.

Removed oil pump (which is only 1700 miles old BTW) expecting stripped gear / broken shaft or something of the sort. The pump seemed absolutely fine!!!

Refitted and left filter cartridge loose; started engine, copious oil leakage. Tightened everything up..... 60 psi oil pressure on gauge, problem solved, back to rally. 2 minutes later oil pressure dropped to a max of 30psi ... back to garage for advice. Stopped engine and restarted it 2 minutes later.... zero oil pressure ..not a flicker. Several subsequent (brief) starts - nothing, no pressure.

PLEASE does anyone know what is going on? Obviously one possibility is the pressure relief valve sticking open but would that really result in no recorded pressure at all with a HC, HP pump and cold, thick oil?

An added "by the way", of the six twin cam Lotuses in our class by the end of the event three of us had surging low oil pressure (or none in my case) and all three of us have fiteed new HP HC oil pumps in the very recent past. Might there be a faulty batch out there?

Any help would be very much appreciated as the car gets rescued back to me tomorrow and I need to sort out what is going on.

(The good news is that the Elan Sprint Coupe of Graham Walker finished second overall on the 3 CAstles - a fantastic result.)

Many thanks for any suggestions.


Roy

[alaric]

Hi. Sounds a bit scary. I had a problem with my engine when I first started it after rebuild, and had to take off the oil filter and crank the engine to get the pump to prime itself. Without the oil filter the oil appeared very quickly and all has been fine since. I'd be replacing the oil filter, pump and looking closely at the relief valve. Presumably the oil level is high enough for the pick up pipe etc. and there's no reason to believe the pick up pipe is allowing air into the inlet side. Hope you get it sorted soon.

All the best.

Sean.

[Roy Gillett]

Forgot to mention, oil level absolutely fine. I wooried that the pick-up pipe might have fallen off, but when it worked again when I refitted the pump I discounted that. Am I right to do so?

Roy

[andyhodg]

Roy

I am right in thinking that the pump drive gear is secured to the shaft with a roll pin? If so have you checked that it is intact? Could the gear be spinning on the drive shaft when the engine is hot?

Also is the jackshaft on good order? may be stripped / worn teeth on the jackshaft oil pump gear? I seem to recall a fairly recent post from Rohan mentioning beefing up the oil pump drive gears if running a high pressure / high capacity pump.

Good luck

Andy

[GrUmPyBoDgEr]

So the Pump pumps when you remove the resistance offered by the Oil Filter but it doesn't when faced with that resistance.
You don't mention if you've tried another Pump which would be the quickest & easiest thing to do.
Heavy scoring or excessive end float caused by ingression of contamination in a Pump would cause the problems that have been described.
If the Pump is OK then the problem lies in a fault on the suction side of the Pump, probably a fractured or loose suction Pipe.

Good luck
John

[Roy Gillett]

Roy

I am right in thinking that the pump drive gear is secured to the shaft with a roll pin? If so have you checked that it is intact? Could the gear be spinning on the drive shaft when the engine is hot?

Also is the jackshaft on good order? may be stripped / worn teeth on the jackshaft oil pump gear? I seem to recall a fairly recent post from Rohan mentioning beefing up the oil pump drive gears if running a high pressure / high capacity pump.

Good luck

Andy

Roll pin looked fine and I couldn't turn the gear on the shaft when it was off, but its a good point to examine further when I get it stripped down again. If the jackshaft gear was that badly damaged I think the distributor drive would be malfunctioning too. Doesn't it come off the same gear on the jackshaft?

I have the 'old' low pressure pump that came off and I will try that first. I am beginning to suspect the suction pipe. There is a gland nut (is that the right technical description?) where it fixes back to the block which I guess could be loose but why does it seal sometimes if that is the cause?

John, the engine did produce full oil pressure with the filter tight when I replaced the oil pump but only for a few minutes.

Its the first you see it, then you don't nature of the fault that is troubling me most!


Thanks for the suggestions , very valuable to have something to go at when I get started.

Roy

[rgh0]

Even with the relief valve jammed fully open I would be surprised at zero pressure with HP / HV pump and cold oil.

If the pump stopped working the idle speed should increase and you should get some bearing rattle very quickly did you experience these symptoms?

Have you checked the gauge itself, perhaps a kink in the line feeding it?
Do you have and oil cooler with a thermostat - some problem there maybe?

An intermittent air leak in the oil pick up I guess is possible but hard to see how it would happen. Maybe a blockage in the intake strainer that comes and goes?

more investigation certainly needed for this one

cheers
Rohan

[Roy Gillett]

Even with the relief valve jammed fully open I would be surprised at zero pressure with HP / HV pump and cold oil.

If the pump stopped working the idle speed should increase and you should get some bearing rattle very quickly did you experience these symptoms?

Have you checked the gauge itself, perhaps a kink in the line feeding it?
Do you have and oil cooler with a thermostat - some problem there maybe?

An intermittent air leak in the oil pick up I guess is possible but hard to see how it would happen. Maybe a blockage in the intake strainer that comes and goes?

more investigation certainly needed for this one

cheers
Rohan

Hi Rohan

I was hoping you might come to my help on this one. You have been on the money with a couple of other problems I have had over the years!

I didn't notice an increase in idle speed, but the engine has run very gently for about five minutes with no obvious rattle or knock to be heard when I briefly got the oil pressure back (and the pressure was normal for a few minutes) I think the pump was definitely going round even if it wasn't generating a measurable pressure.

I hoped at first that it was a gauge fault but I don't think it is. Two reasons: first I could blow down the capilary tube when it was disconnected from the gauge so I don't think it was blocked (even though no oil came the other way with the engine running) Secondly when it was registering no oil pressure I was not getting oil spewing out from a loosened filter so I don't think a pressure was being generated.

I do have an oil cooler fed from a sandwich plate above the filter cartridge but no thermostat on it. When I had had the pump off and put things back together I left the sandwich plate out isolating the cooler and got pressure so I put it back in the circuit and still had pressure for a few minutes before it slumped again.

The strainer is really big on the oil pickup tube so I am really having difficulty thinking something could completely block that.
I am perplexed by the intermittent nature of the problem and like you find it difficult to see why the suction tube should feed the pump one minute, allow a low oil feed the next and then allow no flow once the engine had been switched off. I am also beginning to worry about my bearings as well now as the engine did run for a few minutes with nothing showing on the gauge. Any thoughts?

Roy

[rgh0]

Unless you find some reason for the problem in the pump or gauge you really need to drop the sump and check the pick up. If you do that you can check the bearings.

If you do find a reason and fix it without dropping the sump then run the engine and if no rattle and good pressure bearings are probably Ok.

I would not expect major bearing damage from a few minutes running with no pressure at idle. No pressure and full load / rev for a few minutes and I would have expected total bearing failure and really big bearing knock before the failure.

good luck
Rohan

[AussieJohn]

About 40 years ago I saw a lotus motor which had oil pressure at low revs but if you revved it quickly no oil pressure. Turned out to be a steel plate in the oil pickup breaking loose, if you increased the revs slowly the plate stayed at the bottom of the pickup, if you revved it quickly then the plate was sucked up covering the pickup pipe, a longshot but another possibility. Remember that the strainer is big but the pipe is very close to the bottom of the sump.

[Roy Gillett]

I have now got the car back and have spent the day taking the sump off. The good news is there were no solid particles of any sort in the oil. I filtered it and no solids were found. So I think my bearings are OK. Unfortunately I cannot find anything which accounts for the symptoms. The only thing not exactly as it should be was that the strainer cage at the bottom of the suction tube had become detatched from the spring-loaded plate so when the sump was dropped it fell off into the sump but with the sump in place it could not have moved far (could it?) and I don't see how it being loose could block the suction tube and cause no oil to be moved. Or am I missing something? The tube is tight in the block and 6.5 inches from block face to tip, exactly as the books say it should be. No signs of damage at all.

I have ordered a new HC HP oil pump and I will strip the current one down and look for damage there.

Rohan suggested that I check the bearings just to be on the safe side. My question is do I have to check them all or would looking at a couple give me a clear idea of their condition? If so which would be best; a main or a big end?

By the way 4 and a half litres of oil came out of the engine so I was certainly not short of oil and it was pleasingly clean .

All thoughts and suggestions STILL gratefully received.

Roy

[RotoFlexible]

Roy,

I had a problem getting pressure with a sandwich plate containing a thermostat. I got pressure when I installed the cooler last fall, but the car sat all winter and in the spring I couldn't get anything - no pressure, no oil at the pressure port - despite vacuum to that port, pressure to the crankcase etc. It just wouldn't prime. As soon as I removed the sandwich plate - copious oil, full pressure, no problems. I have not refitted the cooler. I also have a HC HP pump.

[GrUmPyBoDgEr]

I have now got the car back and have spent the day taking the sump off. The good news is there were no solid particles of any sort in the oil. I filtered it and no solids were found. So I think my bearings are OK. Unfortunately I cannot find anything which accounts for the symptoms. The only thing not exactly as it should be was that the strainer cage at the bottom of the suction tube had become detatched from the spring-loaded plate so when the sump was dropped it fell off into the sump but with the sump in place it could not have moved far (could it?) and I don't see how it being loose could block the suction tube and cause no oil to be moved. Or am I missing something? The tube is tight in the block and 6.5 inches from block face to tip, exactly as the books say it should be. No signs of damage at all.

I have ordered a new HC HP oil pump and I will strip the current one down and look for damage there.

Rohan suggested that I check the bearings just to be on the safe side. My question is do I have to check them all or would looking at a couple give me a clear idea of their condition? If so which would be best; a main or a big end?

By the way 4 and a half litres of oil came out of the engine so I was certainly not short of oil and it was pleasingly clean .

All thoughts and suggestions STILL gratefully received.

Roy

Being at the end of the Lubrication train in that area, the Big Ends will be the first to let go.
But since you've opened the Can why not look at them all?

[AussieJohn]

If the strainer was loose and not being pushed by the spring then what stops the strainer being sucked to the bottom of the pickup pipe?

[Roy Gillett]

If the strainer was loose and not being pushed by the spring then what stops the strainer being sucked to the bottom of the pickup pipe?

Good point in one way but it was still up against the sprung plate. There is just no way it can escape that to my way of thinking. Still if everything else is eliminated I may have to believe that that is what was happening.

Roy