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P38 drinking oil


poohbear

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High all,

Just after a concensus-

4.0 Gems, 156k, has had headwork done recently but by previous owner so don't know what.

I've had it 6 months and it's used around 4ltrs oil. Until today it has shown no obvious signs of burning or dropping any. Minor coolant useage but this may be down to not topping up properly having replace heater matrix o-rings.

I'm going to pull the plugs and have a look but what are the usual suspects - I'm guessing at valve guides or rings - or could this be left over after whatever caused the problem that needed the headwork douing. Is it worth trying to resolve or best got shot of?

Dave.

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What mileage has it done in that six months, to have consumed 4 litres of oil?

First things I'd check are the various crankcase-breathers, and whether the oil is the right grade: someone might have filled it with 0W30 or something similarly daft.

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Hi Tanuki,

It's only done 6k un 12months - average 100 m/week in my ownership, mostly short commutes.

Don't know about p/o but I've only used 10/30 part synth - had to fill from well under min when I got it.

There is no sign of smoke at start up or under normal driving. Now I've been looking for it there is blue smoke when you boot it and when the throttle is blipped on the drive.

Will be doing a compression test at the weekend, I'm leaning towards rings, bu we'll see.

Just a thought - can a badly set-up lpg system cause excessive oil use?

Thanks,

Dave.

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  • 3 weeks later...

Thanks for the replies. Still waiting to carry out a compression test - chuffing cold at the moment! Will try and get it done this weekend. Good news is that coolant level hasn't changed since original post, I need to do a proper calculation on oil usage.

Should a compression test be run with the engine hot or cold?

Anybody able to suggest a supplier of decent priced mineral oil? - I've been using standard motor factor semi-synth 10w40. The manual doesn't make any mention of 20w50, from the owners handbook -

"Oils must meet RES22.0L.G4 or CCMC G4 or API service levels SG or SH

5W/30 -30'C to +35'C

5W/40,5W/50 -30'C to +50'C

10W/30 -15'C to +30'C

10W/40 -15'C to +50'C"

If it's (as suspected) worn rings then anything to help oil usage would be good until I work out whether to rebuild or sell on.

Dave.

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  • 4 weeks later...

OK - finally had a chance to spend some tome on the truck. Pulled all the plugs and found no. 6 to be wet with oil - which is kind of what I expected to find.

Couldn't do a compression test as the 'cheapo' tester I bought won't hold pressure. I'll have to have a play and see if I can make it work.

So there is definately something amiss with no.6, next job will be rocker cover off for a quick looksee. Question is as the oil useage is down to a fault on one cylinder rather than just general wear, will changing to 20w50 mineral oil make any difference?

Dave.

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  • 2 weeks later...

Quick update:

flushed and changed oil out for 20w50 mineral as suggested and (so far) visible signs of oil burning have gone :). It has only been a few days and not many miles so I need to see how much of an improvement this has really made, but so far things are looking good - Many thanks to Chris for the advice.

As Idon't have the luxury of a workshop I'll do a proper compression test once the weather is a bit 'friendlier'.

Dave.

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  • 1 month later...

Quick update -

Still using oil - only obvious symptom is cloud of blue smoke when first pulling away in the morning. I've changed the pcv hoses and cleaned the oil seperator in the rocker cover with no improvement. I have had bank 2 rocker cover off in the process and I'm sure that at least one valve stem seal has lifted off the valve guide, I can actually see the top of the guide on no. 6, which would explain the blue smoke.

Assuming I can use the adaptors from my compression tester to pressurise the cylinder with compressed air, how can I compress the valve spring enough to get the collet out and replace valve stem oil seals?

Or is this a head off job?

Dave.

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  • 4 weeks later...

Years ago successfully changed stem seals on a Cavalier by pressurising the cylinders. We brazed a PCL fitting into an old spark plug without a middle. Remove oil filler cap before doing (there is a fair bit of leakage, and you'll need a reasonably beefy compressor) and have piston at tdc (in case it drops, then at least it can be retrieved...) Hardest thing I'd imagine is to find a spring compressor, though Sealey used to do one.

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Valve-guide oilseals can harden with age - they can also get knocked-out quickly if the valve-guides have worn and there is significant 'slop' allowing the valve stems to rock in the guides.

Still, new stem-seals are a cheap/quick thing to try. I always used to do them by pulling the spark-plugs then stuffing a length of thick cord into a cylinder and rotating the engine with a wrench on the crank pulley so the piston rammed the cord up against the inlet-valve.

Only engine this fails on: the 2.6-litre 6-cylinder 1960s IOE Land-Rovers. Which can really develop an oil-appetite when the valve-guide seals harden with age. 100 miles per pint of oil leaves a nice blue haze behind you...

--Tanuki.

"Badgers are never the answer, always the problem!!"

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  • 5 years later...

The later V8's (Disco 2 / P38 era) have a different front cover & oil pump to the earlier ones (which absolutely love 20W50 and hate thinner oil), the factory manual specifies lighter oils for the later engines although they will live with 20W50 it's by no means the right answer. Mineral or synthetic has nothing to do with it, just use good quality oil (it doesn't need to be stellar) and do regular oil & filter changes.

The early "external gear" type oil pumps struggled to self-prime or pick up thin oils but from the 3.9 EFi sort of era onwards they moved to the gerotor style pumps, presumably with good reason.

v8_oils.png

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  • 2 years later...

I have a 95 P38 4.0 that has been sitting for at least 2 years.  After getting all the front end (tie rod bar, sway bar, new tires, shocks, etc), I test drove it on the freeway at 80 mph, all of the sudden a slight knocking on the engine, the faster I go the knocks got worst, below 70 mph, no knocks.  I pulled over immediately to check the oil was completely empty.  I quickly bought Lucas oil and used 10w40 and a two days later, it was almost empty again.  I have to mention my P38 does have a bad leak but it's been this way for the past 5 years and it doesn't go empty this quickly, normally would take 3-4 weeks if driven daily with leak.  Does it sound like I have damaged heads and/or engine?

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Did the low oil pressure light even go out at any point?

If you drove it without oil under load to the point that it started to knock, then yes, you almost definitely damaged your bearings and maybe even the crank.

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I do hope when you say 'completely empty' you mean no oil on the dipstick, which means about 1l under minimum level or 2l to top up. Running it completely empty is almost guarantueed to cause damage. 😞

Always check if a car has been sitting for some time... And replacing if over a year old, engines like fresh oil.

I hope it's just a case of the leak getting worse while sitting. If it's a the front the pressure valve at the oilpump is a know cause of severe leaking.

Filip

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