Practically Classics Forum

I took my car out for the first run after fitting a new oil pump (after thinking the old one had failed) and it is EXACTLY THE SAME, ARGH!
65psi when cold at 3k, 43 when warm 3k, 8 when hot idle 30 at 3k. (old pump was 25 cold at 3k rpm dropping to 8 when hot at idle so was definitely on it's last legs)
Off the road for almost 2 months while i check and replace parts, wait to be paid, check and replace more parts and it has acchieved bugger all!
Sorry for the rant. I am mildly annoied with cars at the moment.

Does anybody have any thoughts other than a failed oil pump, what can cause low oil pressure idling when hot?

And that right there is the most common cause of low (or excessively high) pressure if you're talking about your RV8.

Unfortunately that is new too. My v8 is like the one from a disco 300 v8. It has a serpentine front and a distributor. I have fitted a new front timing cover and all the component parts of it.
The car is idling at 900rpm dropping a little bit to 850ish when you put it in to drive and that is when the oil pressure light comes on. I have thought about raising the idle speed a smidge but I would rather find what is causing the problem than mask it as i want my engine to last 20 years. The only problem is i have no idea what else to try :S

Other than worst case scenario of worn bearings or rockers ?......... assuming a basically sound engine....


Just a couple of thoughts that may or may not help, you seem to be improved other than the hot idle having changed the pump.......

Oil pick up mesh / screen partially blocked, oil filter ( some reckoned to be better than others, fram supposedly being one prone to causing oil light flicker), too thin an oil..... if you have miles on her then perhaps a grade up would help ( don't shoot me, just a thought from someone who's run a few high milers and I know it aint politically correct these days), or running too hot and thinning the oil / or possibly causing the relief valve to stick.

Other than that if its the rover v8 type I believe it isn't unheard of, I believe about 10 psi per 1000 rpm is "acceptable" so the 3 k reading while perhaps down a bit is probably ok for a hot engine.

Other possibilities.....if engine sounds well and quiet, sender unit opening on low end of scale / faulty gauge if the readings are from the dash gauge.

Basic engine textbooks say that oil pressure is generated by the restriction of the flow through the main and big end bearings so most engines have their switch and instrument feeds tapped off the oil gallery leading to the crankshaft.
It follows that if you have low pressure, the relief valve is not off it's seat and the pump is not knackered then the bearing clearances are probably too large due to wear
However, a long shot is the guage itself - maybe your transmitter is duff or the guage out of cal. Solution, try a known S items and see if it's OK.
There may be carbon particles in the oil gallery masking the guage and switch outlets - try a brief start and run with the switch and guage transmitter removed, that should flush any sh*t out.
I've heard that slack lifters can also make the oil pressure dive, I've listened to some pretty clattery valves on Mitsi V6'S but the OP was always OK.
If all else fails you can live with it, probably quite safely but I would be the same as you If I had done such a lot of work and spent so much cash and I would want it sorted
Rover V8 gurus out there - does this lump have known OP issues

Thanks for the suggestions all. I have spent some more time fiddling today and not really achieved anything as I am not in the mood to lie on my back and take the sump off this weekend. I've got it booked in on Monday to have someone check the big end bearings but I don't think there is an issue with them (or should that read I hope there isn’t). The engine sounds really sweet and has only done about 20,000 miles. However the specialist thinks the main bearings are the only thing it can be :S.

The oil pickup strainer is clear, it came off when the sump was off to replace the gasket after doing the pump. There was some carbon on the strainer but nothing obstructing it.

I am inclined to trust the gauge (it’s one you remote the pressure switch for and screw in rather than one on the dash). I have a new oil pressure sensor and both the new one and original flicker the light when in drive at idle (550rpm on the dash but 650 in reality)

I have noticed that idle bounces about 50rpm from 700-750 at idle and 550-600 in drive when hot. That’s right at the bottom of "normal". Plugging in my diagnostic computer it says "idle speed control failure" and "check for plenum air leaks and stepper motor connection". The stepper is OK (if I pull it out and run a test it cycles in and out cleanly) I can’t find any air leaks by spraying brake cleaner about but I have ordered a new stepper just in case. If I disconnect it and block off the bypass hose I can get a stable idle at 750 / 600 (idle no load / idle in drive) but the oil pressure light still flickers. If I force the idle up to 900 / 750 (the top of normal) by disconnecting the stepper, opening the air bypass and advancing the timing then there is no oil pressure problem, it holds 25psi but pinks like mad under load. With the timing set correctly it drops the idle speed down again and flickers the oil pressure light.

As this is a late one with a crank driven oil pump it is not known to have issues with oil pressure rather than the earlier ones with the oil pump driven from the dizzy that was only just adequate. The LR man did say that i'm not going to break it by driving it as it has plenty of pressure when the revs are up. I'm very tempted to get rid and buy a TVR though. I must be getting old.

Sorry to wuss out and call someone but it was either a mechanic or the scrap man.

Once did a range rover that had the wrong oil filter on it and the internal valve in the filter was incorrect and caused pressure problems.
Dont suppose its got a big dent in the sump restricting the oil pick up.

No dents i'm afraid. I might bend the pickup tube slightly for a bit more clearance though just in case. 4.6 engine, 4.2 sump. I'm not sure what the difference is but i know the 3.5 one is shallower.
I always use genuine filters but when this first started I had a genuine one on. First thing I tried was a replacement Wix filter as it is what my local motor factors had in stock. Today it has had another genuine filter then a halfrauds one just in case i had a dodgy batch of genuine ones.

This is a REALLY confusing problem. There is nothing obviously wrong but it's not working properly. Classic cars are a pain in the bum!

I would say as long as it runs well, doesn't sound like a bag of nails, and doesn't overheat are you worrying unnecessarily and simply suffering from a case of gauge paranoia?...........look at it this way, if you didn't have an oil pressure gauge to look at, would the engine actually be giving you any reason be worrying about oil pressure?

Searching around shows the flicker at idle to be quite common, two things interested me when searching the net..

1, many swear by a good quality 15/40 or 20/50 oil ( though when on the web we have to remember a lot of posters are in hotter climes), which I imagine is a fair bit heavier than LR reccomend but does seem to be a popular choice.

2, another possibility on top of those mentioned already, probably unlikely and definately not one you really need is a slipped cam bearing. This link covers it some http://www.discoweb.org/forums/showthread.php?t=40179