Using oil only when on boost

[Heaveho]

In general, is it safe to assume that if a turbocharged car is using oil only when driven on boost for extended periods, the turbo is the culprit? It uses none on extended, off boost motorway trips. Performance is unaffected, people who have followed the car when it's being driven on boost for extended periods say that there's nothing visible from the exhaust, yet during such use it can use more than half a litre per 1k miles. The car is a stage one Evo 9 running 1,8 bar peak boost.

[Krikkit]

Do you still have the oil breather venting into the inlet? Might be worth fitting a catch-tank to rule out if it's the turbo or the rings.

[Heaveho]

Hi, yeah, the general setup is completely factory, so possibly worth trying. I had to replace the turbo ( which was the one under suspicion ) last year, as it broke up internally, and I haven't driven the car much at all since then, so it's possible it's already resolved. I replaced it with another original Evo 9 item which I knew had done less than 1k miles. I'm off to Spa in the car in a fortnight or so, I'll make a point of driving it hard on that trip and see where it's at as far as consumption's concerned.

I'm interested in how it could use oil, yet display no visible signs of doing so except for on the dipstick.

[E-bmw]

I agree that it is a lot to keep topping up, but 1/2 litre in 1000 miles you wouldn't see externally.

Some BM 6's can use double that with no outward signs at all.

[Heaveho]

I had a Corrado VR6 several years ago, and after nothing but Japanese cars, it came as quite a shock to have to do regular oil level top ups. Oil consumption does seem to be more likely with German cars from what I read, although, in fairness, my current Boxster doesn't use a drop.

Given the fact that the Evo seems generally to be in rude health, I'm not at all worried about the consumption, but it's obviously something I've introduced with the mods I did at 30k, as it didn't use a drop until then. It seems clear it's head or turbo related as they were the only things changed that could have had any instant effect. To my mind, it eliminates the rings as a possibility. This is the first of many Jap cars I've owned that has used any oil.

[Mr2Mike]

Oil use under boost could be down to excessive blow-by overwhelming the engine breathers, or a problem with the breather system itself. High boost conditions usually helps to keep oil within the turbo bearings, which is why knackered turbos tend to smoke a lot at idle.

[GreenV8S]

Heaveho said:

The car is a stage one Evo 9 running 1,8 bar peak boost.

That sounds like a lot of boost to me, and I would not be surprised if emissions, oil consumption etc were very different under those conditions than in normal gentle driving. Do you know what is the typical oil consumption for a similar engine under those conditions? Half a liter per thousand miles is on the high side for a typical road car but not completely unreasonable for a tuned engine driven hard.

[Heaveho]

GreenV8S said:

That sounds like a lot of boost to me, and I would not be surprised if emissions, oil consumption etc were very different under those conditions than in normal gentle driving. Do you know what is the typical oil consumption for a similar engine under those conditions? Half a liter per thousand miles is on the high side for a typical road car but not completely unreasonable for a tuned engine driven hard.

Hi, Evos tend not to use oil at this level of modification. It's a lot of boost, but a lot of Evos run this setup without experiencing this issue. It's usually when running forged pistons that this issue rears it's head. It ran 1.8 bar on the original, smaller turbo at about 320 brake for several thousand miles without a problem before I changed the head and turbo. It makes just shy of 400 now, feels very strong, and drives as well as ever. Considering how shocking they are on fuel, surprisingly it's within a whisker of being within the permitted allowance for emissions with the cat removed. Found out when I forgot to replace it come MOT time one year.

My VR6 used a litre or so every 1k miles, and most owners I spoke to when I had it said theirs were similar!