Well Saturday was a busy one.....

Gearbox fluid and filter change on the L322 and then I set about taking the oil pump drive out of the P38 and replace with new gears....

I finished at 1.40am after a long slog doing both jobs, but seems it was all for nought!

Took the front cover off and checked the original gears against RAVE tolerances, the gear to Gear rotor tolerance is a maximum of 0.25mm and using feeler gauges (can only just get the tip of it in the gap) it would appear the gap is on that limit, and also the gap across the top of the gears to the timing chain cover is a maximum wear of 0.1mm and as can be seen in the photos I can get the 0.1mm gauge nicely under the flat edge.

Anywho, I replaced with new gears and refitted the pump cover and torqued the screws and bolt correctly to 4Nm for the screws and 8Nm for the bolt.......the new pump gears were very tight in the housing whereas the old ones did move, and so does the oil pump drive in the original timing chain housing.

On start up the oil pressure didn't rise until you got above 2.5K rpm and once at idle for longer than 15 seconds the pressure light would come on again until you revved it for a few seconds again!

Drove home Sunday morning and while driving all is well, stop at lights and the engine is at idle, 10-15 seconds later, the pressure light is back on again until you drive it and get above 2K rpm and then the light goes out until you sit at idle again......

Reason for the change was it did the same thing before I changed the pump gears, only I didn't need to get it to 2K for the light to go out....up to 1200 and back was enough to extinguish the lamp.

Question is, do Oil Pump Gears need to bed in or should it be fit and forget??

Also, I still have the original Timing Chain Cover that has a crack in it, but has the oil pump fitted (didn't have pressure issues with this one) so do I fit the gears from this cover and see what happens or seeing as though the replacement TCC has new gears in it, it must be an issue in the TCC itself...maybe the oil pressure relief valve?? But I would have thought that would go at high revs not low??

Thoughts? Looking to do reworks possibly Friday!

pump in pics looks ok and is not the cause of your problem, new gears are fit and forget

+1 on the new gears. partially blocked oil strainer, faulty oil pressure switch, worn main bearings ?

Pressure switch first, rule the easy one out

Thanks chaps....New switch fitted previously.....

http://www.landyzone.co.uk/lz/f10/oil-pressure-switch-replacement-260498.html

Thicker oil may help in the short term.

Datatek said:

Thicker oil may help in the short term.

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Was considering this, using 15/40w at the moment!

Could use 20/50w....!!

Considering removing the relief valve and checking spring free length )should have done this when it was off - stupid mistake!!) as getting to the relief cap and then if the cap is stuck, trying to get the cap off with it attached to the car will be a pain!

Speaking with one of our Hydraulic guys, we are looking to plumb in a temp pressure gauge and see what the readings are!

Sounds like you need EP90 What a pain, always worth doing an actual pressure check before diving in.

oil pressure relief valve will have to be stuck open to give you grief. orv relieves high pressure which you are lacking at lower revs

tomcat59alan said:

oil pressure relief valve will have to be stuck open to give you grief. orv relieves high pressure which you are lacking at lower revs

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Correct but he needs to look at the pressure switch first. I have seen engines stripped because of a duff pressure switch. Pump didn't look to bad, but he didn't show us the ends of the rotor. Didn't see anything there to cause such a dramatic pressure loss. If it's not the switch it has to be the mains or the relief valve stuck open has been known. **** thin oil in an old engine will not be helping a lot.

wammers said:

Correct but he needs to look at the pressure switch first. I have seen engines stripped because of a duff pressure switch. Pump didn't look to bad, but he didn't show us the ends of the rotor. Didn't see anything there to cause such a dramatic pressure loss. If it's not the switch it has to be the mains or the relief valve stuck open has been known. **** thin oil in an old engine will not be helping a lot.

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Totally agree, I was stupidly assuming the new o/p switch was working correctly. proper oil pressure gauge needed to check pressure.

tomcat59alan said:

Totally agree, I was stupidly assuming the new o/p switch was working correctly. proper oil pressure gauge needed to check pressure.

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Yep switch should put the lamp off at around 15 psi. Max pressure will be around 50 psi. Pressure relief valve should only come into play at higher rpm with cold oil.

Pressure switch is fine, it was fitted to the old Timing Cover as I thought it may have been there that the oil leak was from...which it wasn't....I had no pressure issues with the old timing cover or when it was fitted with the new switch.

New switch was swapped onto the replacement TCC, but will be doing a pressure gauge check in anycase.

The relief doesn't relieve to atmosphere as it is a closed system, it relieves into the oil filter bowl! So if the relief is relieving early (low psi) then the pressure is going straight to the filter and on to the system rather than up the pipe to the pressure switch...until such time that the revs and oil pressure are high enough to go past the relief valve, into the filter bowl AND up to the pressure switch turning the lamp off.....

Is just a theory, but as you say, until I do a live gauge reading, we'll never know....trouble is, I will port into the Pressure switch port which if my theory above is true will prove nothing other than either low pressure at low revs (as it is bypassing the relief valve prematurely) or high pressure (when the lamp switches off anyway!!)

Ho hum....will keep looking!

Saint.V8 said:

Pressure switch is fine, it was fitted to the old Timing Cover as I thought it may have been there that the oil leak was from...which it wasn't....I had no pressure issues with the old timing cover or when it was fitted with the new switch.

New switch was swapped onto the replacement TCC, but will be doing a pressure gauge check in anycase.

The relief doesn't relieve to atmosphere as it is a closed system, it relieves into the oil filter bowl! So if the relief is relieving early (low psi) then the pressure is going straight to the filter and on to the system rather than up the pipe to the pressure switch...until such time that the revs and oil pressure are high enough to go past the relief valve, into the filter bowl AND up to the pressure switch turning the lamp off.....

Is just a theory, but as you say, until I do a live gauge reading, we'll never know....trouble is, I will port into the Pressure switch port which if my theory above is true will prove nothing other than either low pressure at low revs (as it is bypassing the relief valve prematurely) or high pressure (when the lamp switches off anyway!!)

Ho hum....will keep looking!

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Don't think you will find the oil flowing into the filter bowl from the relief valve Ant. The filter is on the pressure side of the pump. Oil is drawn from the sump through the pump and into the oil cooler then through the filter into the pressure galley. Any excess pressure released by the relief valve just drops back into the sump.

wammers said:

Don't think you will find the oil flowing into the filter bowl from the relief valve Ant. The filter is on the pressure side of the pump. Oil is drawn from the sump through the pump and into the oil cooler then through the filter into the pressure galley. Any excess pressure released by the relief valve just drops back into the sump.

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Over pressure oil is returned back to the pump via the filter bowl....I believe there are two relief valves (I can see the spring to the second, but haven't had the cap off yet to confirm - will do shortly) Photo of the relief valve bypass into filter bowl and also the second relief valve spring....also I have drawn a schematic of the oil flow in the cover for reference.



So if the main relief is bypassing, it would have to also get past this second valve too to reurn to the pump for recirculation!!

Will check for existence of second valve, it may just be a spring to hold the dross drilling caps in place!

thats a very nifty little picture youve got there Saint!

My understanding is the prv on the left is the one which vents excess pressure back to the sump and the one on the right is the oil filter bypass valve in case the filter is blocked.

sassanach said:

My understanding is the prv on the left is the one which vents excess pressure back to the sump and the one on the right is the oil filter bypass valve in case the filter is blocked.

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Correct, if the excess pressure vented to the filter it would blow the filter sealing ring. I know, the sleeve on the relief valve on a XJ40 became loose and lifted with the valve so preventing the excess pressure venting. Luckily the filter seal blew before any of the engine oil seals

OK, had the second valve apart and yes, it is indeed a relief valve.

I think Sassanach is correct as one of our Hydraulic guys also said the same thing while I was downstairs, and Sassanach has just repeated the same thing!

Photos attached for your indulgence....

Soooo, given all the above, do we reckon it is a relief valve issue or something more sinister??

Can you not put the old cover back on?