Low oil pressure

[paul mc]

Hi,

After a slow 2 year build of my Series 3/RRC i've finally SVA'd and on the road, but now that I am using it for longer (not just test runs around a field to test bits) it is clear that the oil pressure is low, the hotter the engine gets the lower the pressure gets and after a longish drive the pressure really drops on tickover and sometimes the top end sounds quite tappetty. I am using 20w-50 and have tried the oil additives aswell just to see, I have replaced the pressure relief valve with the tadpole type from JE, and the housing for it looks like its in good condition, as much as i can tell anyway.

It's a 3.5 V8 EFi wit 170k done, so it is fair to say the engine is worn out. I did a basic top end refurb during the rebuild (head and exhaust gaskets and re-ground the valves) and everything looked pretty good. I will eventually get round to a full rebuild but for now I'm just trying to keep it working and economically viable, I have spent much more than planned so i don't want to fork out for full rebuild kit yet. But basically, I can only think the next and simplest thing to do is replace the bottom end bearings (big end and main) and fit new oil pump gears while I'm under there. But what I want to know is can i do the bearings with the engine still in the car by just removing the sump? I have an inspection pit so access is good but I haven't really ever looked into the engine from below so don't know what is and is not possible.

Also, is there anything else i should be doing while I'm under there, oil seals etc?

I'm not really worried about restoring it to original condition at the moment, I'm sort of treating it as a phased rebuild, so that I can keep doing bits and pieces to the engine which will all help but won't need re-doing if i get round to a deeper rebuild.

I'll probably replace the cam shaft for a 3.9 one eventually and then worry about new tappets, rods and rockers then. The compression is consistent in all cylinders and up to spec so no worries there.

So please, any advice for increasing pressure and fitting new bearings greatly appreciated.

Thanks,

Paul

[Bowie69]

You can do big ends but not mains by removing the sump, good idea to refurbish the oil pump, at that mileage its probably very worn by now!

[Snagger]

I have never worked on a V8, but I have built a 12J, a Tdi and worked on some other 4cyl units. If you can access the main bearing caps with the sump removed, you should be able to replace the main bearings too - the clutch will hold the rear of the crank shaft in place and the front seals will support the front end, but there should be enough give to slide the main bearing uppers out by using the lower halves (from inside the caps) as pushers - once the upper shell is part way out, you should be able to get them out with fingers or with some water pump grips. Alternativel, some stiff but soft wire could be used to push the shells all the way around the journal until they clear their block seats and drop out.

Fitting the new shells would be more difficult as they'll have their full thickness, but covered in oil they should slip onto the bottom of the journal and spin around into their seat if the crank is pulled down to give as much clearance as possible (don't pull so hard as to crush the oil seals at each end). It'd certainly be possible on a 4 cyl like a Tdi, if fiddly, buy I can't be certain of a V8. However, given that the crank is thrust downwards by the compression, combustion and exhaust strokes, most wear would be on the lower shells and comparatively little on the tops, so if you can't easily remove the tops, don't damage them by persisting - just replace the lower shells with the matched (presumable standard) size and most of the wear will be taken up. It's far from ideal, but it should sort some of the oil pressure loss. All of this assumes the crank shaft is not worn badly, though, and the cam shaft and bearings are notorious on the V8.

[paul mc]

Thanks for the replies, I took the sump off today to have a look and see what i could do, the big end bearings will be fine to do with the engine in place and the main bearings look do-able, i managed to get the old bearings out easy enough as Snaggers suggestion, and I have now ordered all the bearings i need so i shall try and replace them next weekend, hopefully it will work.

I'm glad i am doing it, the bearings i removed are very warn so new bearings should really help with the pressure.

I'll let you know how i get on with fitting the new ones.

Cheers, Paul

[Quagmire]

Check the pump too, replace the gears if needed and check the base plate for scoring.

If it is scored then you can resurface it by lapping it on a piece of wet and dry laid on a piece of plate glass. Make sure you use nice even figure 8 motions and you'll soon have a nice flat pump base.

That should help up the pressure a bit

[Fett]

I had a similar thing but my engine is ultra low milage.

I ended up stripping the pump which isnt low milage and found the base plate was scorred. we flattented it back and fitted high vol oil pump gears from real steel which was only about £50. we replaced the relief valve for a standard one as we found it was sticking a little which could have been the cause or part of problem and it works a treat now , I am off the chart at cold idle and when very hot at low idle I still have 27 pounds. its worth looking at the pump gears and valve before shelling out mega bucks on a rebuild . mind you having said that you are a running a very high miles engine.

[paul mc]

A bit of an update then.

I have now replaced all of the main and big end bearings from underneath, and while it is certainly possible I have an inspection pit, it would have been a thoroughly unpleasant and oily couple of days were i working on my back. I drained the oil and removed the sump friday night and it was still dripping oil the next day, but as i was standing under the vehicle it wasn't so bad.

The big end bearings were a piece of cake but the main bearings took some some fiddling. I made up a bit of metal a little narrower and thinner than a main bearing shell which i used to tap out the top bearing (obviously I spent a long time rounding all of the edges so i wouldn't risk scratching the crank). Getting the new main bearings back in was little fiddlier but i undid all 5 of the main bearing caps and it allowed me to gently tap the new ones home with a block of wood, i did the two end bearings first which openeed up the clearance a bit for the three central bearings, making it easier.

I also fitted new oil pump gears and refaced the oil pump base, it has all helped but still not restored the pressure to anything like specified.

I did see those high volume oil pumps previously but they are all described as being for pre-SD1 engines, so i didn't think they will fit my 1987 unit, Fett, what engine did you fit it to? Or has anyone else used these high volume pump kits?

Thanks,

Paul

[Fett]

Hi , yes mine is pre 76 . I didnt realise they were not available for the later engines though.

It might be worth calling real steel or others like them to ask what is available.

[Simon says]

A bit of an update then.

I have now replaced all of the main and big end bearings from underneath, and while it is certainly possible I have an inspection pit, it would have been a thoroughly unpleasant and oily couple of days were i working on my back. I drained the oil and removed the sump friday night and it was still dripping oil the next day, but as i was standing under the vehicle it wasn't so bad.

The big end bearings were a piece of cake but the main bearings took some some fiddling. I made up a bit of metal a little narrower and thinner than a main bearing shell which i used to tap out the top bearing (obviously I spent a long time rounding all of the edges so i wouldn't risk scratching the crank). Getting the new main bearings back in was little fiddlier but i undid all 5 of the main bearing caps and it allowed me to gently tap the new ones home with a block of wood, i did the two end bearings first which openeed up the clearance a bit for the three central bearings, making it easier.

I also fitted new oil pump gears and refaced the oil pump base, it has all helped but still not restored the pressure to anything like specified.

I did see those high volume oil pumps previously but they are all described as being for pre-SD1 engines, so i didn't think they will fit my 1987 unit, Fett, what engine did you fit it to? Or has anyone else used these high volume pump kits?

Thanks,

Paul

Worn cam bearings and worn rocker shafts & rocker arms may need investigating,although not necessarily in that order as the cause of your lost oil pressure.

[SteveRK]

I wouldn't think that replacing the big ends, or main bearings will have any noticeable effect IF the original shells were still showing 'grey'. The new shells will need to be progressively run-in to avoid premature failure as they will be initially contacting on the high-spots on the journals. Once bedded in you will be back to where you were before replacing them after around 1,000 miles or so.

The best check will be to fit a pressure gauge? And IF the oil light is not coming on then i don't think you have a pressure problem but might well have some tired hydraulic tappets instead giving the impression of low pressure.