P38A High Oil Consumption, 4.0 litre V8.

My daily drive P38 has rather a thirst for oil, using about 3.0litres/1000miles. It drives great and fuel consumption on mixing driving is about 15.4 mpg. I'm currently using a 10W/40 semi synthetic oil but wondered whether I should switch to 15W/40 or maybe something even thicker? There are no noticable oil leaks from the engine (surprising but true), and no smoke from exhaust except under hard acceleration.
The engine has done approximately 135,000 miles, the heads were done by a local Range Rover specialist approximately 3,500 miles ago and it's not using any coolant.

I would appreciate some comments and advice from the wise folk of the forum.

theres lots of places for an oil leak, 3L/100 miles is rather a lot, are there no obvious signs? what colour is the smoke?
I use 20w50 standard oil, not semi/fully synthetic which does have a higher tendency to find weak points

Hi Kermit, there are no obvious signs of a leak. There is never a drop of oil on the drive where I park it. The smoke under heavy acceleration is blackish but I think that I may be exaggerating slightly as although I can see the smoke in my rear view mirror it's really not that bad.

black smoke is sign of an over rich mixture, although to be visible from the rear view mirror, there must be something wrong.
if you're burning any quantity of oil, the cats wont love you

Okay, thanks Kermit. I think I may have exaggerated the smoke but maybe I should change to a thicker oil?

lets see what other come up with, i dont know if simply swapping to a thicker oil will solve this

Compression test
If it’s not dripping it’s eating it.

If I change to thicker oil do you think the oil consumption will improve?

swac said:

If I change to thicker oil do you think the oil consumption will improve?

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I would say no, others may disagree, my 4.6 used less than a litre between oil changes, around 5k.

At the rate you get through it, you'll never need to do a change!
Start topping up with 20/50 instead but you'll probably still need to resolve the underlying problem

swac said:

My daily drive P38 has rather a thirst for oil, using about 3.0litres/1000miles. It drives great and fuel consumption on mixing driving is about 15.4 mpg. I'm currently using a 10W/40 semi synthetic oil but wondered whether I should switch to 15W/40 or maybe something even thicker? There are no noticable oil leaks from the engine (surprising but true), and no smoke from exhaust except under hard acceleration.
The engine has done approximately 135,000 miles, the heads were done by a local Range Rover specialist approximately 3,500 miles ago and it's not using any coolant.

I would appreciate some comments and advice from the wise folk of the forum.

Click to expand...

That's better than I got from a brand new BMW 325i Stick some 20W50 in it and see if improves.

Datatek said:

That's better than I got from a brand new BMW 325i Stick some 20W50 in it and see if improves.

Click to expand...

I had one of those, M50 engine, never needed to top up between oil changes, even when I sold it at approaching 1/4 million miles on the clock

20w50 or 10w60 is what should be used in a Rover V8

10w40 is too thin

As for the consumption it is either leaking it or eating it..

Compression test..

Any blowby?

Check your engine breathers are clear.

Regardless of the build date of your car remember that the RV8 dates back to the early 'sixties.
You need a good quality mineral 20w/50, a product with a high ZDDP content will be benificial as the engines' employ 'flat-tappet' technology.
Whether using these products will reduce your oil consumption remains to be seen, but RV8's are not generally known for high oil usage.

But they can leak a bit

Blocked breathers will create crankcase pressure which will force oil past the piston rings.

Thanks for all the helpful suggestions so far gentlemen. I will start topping up with a thicker oil. As far as I know the engine breathes through those pipes which go from the rocker covers to the air inlet manifold and those pipes are clear. Strange thing last night though, and I don't know if this will ring any bells for anybody, I thought I'd have a look under the bonnet before leaving work and I noticed lying on the front ns chassis rail a round aluminium disc, at first I thought it was just the inside of an oil cap which had fallen off as I'd topped the oil up but no, it was one of the two alumium discs which are siliconed into the air ilet manifold (I've no idea why they are there), anyway I siliconed it back in last night refitted it this morning and drove to work as normal. I hope to do a compression test this weekend and will report back. Thanks again guys you really are a great font of wisdom.

Aluminium discs in the inlet manifold? Not aware of these but how did it fall out?

There are two of these on my car Kermit, it's a very late Thor engined car, they look like they are just blanking up some redundant holes in the bottom of the big plastic pipe which goes from the air filter to the throttle body, the holes would be about 30mm in diameter. I thought it was for something that perhaps the GEMS engines had fitted and the Thor engines didn't. I don't know what caused it to drop off but I've been going up and down the M6 the last few days so it must've just happened because I can't imagine it would stay there for long.