M3Cavalry

997.2 with 112k, used a quart in about 900mi (went from full to having no bars illuminated w/o an oil warning, just added a quart). What’s the effect of changing oil type as I replenish it? Specifically, it has Motul 5w40 in it. If I start adding DI 5w40 as needed, what impact does that have? Avoid until I do the next oil change? Thanks!

MrMoose

All the A40 oils are *generally* compatible. If they weren't you'd have issues changing oil brands because there's always some leftover oil in the system. That said, if you're topping off I'd just stick with the same brand, myself: If you want to change brands just do a full change.

If it's using that much oil then changing brands from one 5W40 to another isn't going to make a significant difference, though. Is this a sudden change, or a new-to-you car, or what? It's either going on the ground, going into the intake, or going around the rings or valve seals: you need to try to figure out where.

jchapura

Experts like Lake Speed Jr. suggest not mixing oils because of "additive" clash. In his most recent video, about an oil performance comparison in his "Wombat", he says he's going to do a "double flush" (two oil changes) before he relies on the used oil analysis results to measure engine wear.

M3Cavalry

Car is new to me. Oil consumption seems high compared to my experience in BMWs but I’m tracking that this level of consumption is not technically out of line with how Porsche defines normal.

MrMoose

Yeah, manufacturers will say 1qt/1000mi is within normal expectations, but that's higher than I'd like to see, and higher than typical for a 9A1. Changing oil brands is unlikely to make any difference. If it's something like valve guide seals 50wt might help but that would just be a patch.

I don't believe the 9A1 has the rear main seal issues of the earlier engines. I might check the intake and OVS tubing for excessive oil. No evidence of leakage? Any smoke out the tailpipes, oily tailpipe tips, that sort of thing?

SpectreH

With Mobil 1 oil (5w40), I was going through a quart in 1000 miles. I switched to DI 5w40 and just added 3/4 of a quart after 2000 miles.

Petza914

Do not mix oils, especially the A40 approved Motul that's in there with non A40 approved Driven DI40. The additive package in Driven oils is very different than all the others and why it works so well. Do a complete oil and filter change, put in the DI40 and buy a few extra quarts to have for top ups if your car has one of the "looser" engines that uses oil. Keep one or 2 of those quarts in the car for top-ups when on a longer trip.

yelcab

So it goes from:

It's OK to mix oil
Changing oil reduces consumption from 1000 miles / quart to 2000 miles per quart
...
Do not mix oil.

This is why you don't ask opinion on oil, on the internet no less.

SpectreH

I would add that when I changed from M1 to Driven Oil, I was only looking for a better oil. I was not expecting a significant change in consumption.

Petza914

The reducing consumption comment wasn't from him mixing in different oils over time it was from changing oils at an oil change.

As with any responses here, take the advice of the members you trust the most or think are the most knowledgeable.

MrMoose

Well, no. I was more going for "It's not going to blowed-up your engine but it's not best practice, and if you're looking to make an oil brand change to try to fix this then just change the oil".

I'd only mix oil brands in an emergency situation but if I had to do so I wouldn't worry about it too much. I mean, look: if you change brands at a fill you're already mixing oil brands given there's probably at least a quart of the old stuff left in there. People worry about this crap too much.

ANYWAY, without knowing where the oil's going it's hard to say if a different brand is going to help. Like, I'd definitely want to verify this wasn't an AOS issue before freaking out.

If it's a non-AOS issue then I'd be pretty amazed if switching to another brand of the same weight oil made a significant difference, but sounds like it worked for Spectre so who knows? At this point give it a shot, what else are you going to do? Just bear in mind that Driven's schtick is additional anti-wear additives, and that particular aspect is not going to help a car that's already burning oil. It's quite likely a bit thicker than the Mobil1, which might explain Spectre's results.

I was going to say maybe try Mobil 1 5W-50 as a bit thicker oil, but it looks like when they reformulated that to SP spec recently that it's no longer A40 so I don't know what to tell you on that.

Petza914

In this particular instance, A40 approved Motul xcess is a 5w40 and Driven DI40 is a 0w40 but right on the viscosity edge of being a 5w40 and is actually being relabeled as such, so in the original formulation, Driven being thicker is not the reason the consumption went down. However, we've seen Mobil 1 shear to a lesser viscosity grade pretty quickly, so over the course of a 5k mile change interval, it would not surprise me if consumption with Mobil 1 increased because it actually became thinner than the Driven DI40.

As you mention, because simply doing an oil change actually mixes oil since you don't get it all out is why it's recommended to do an engine flush with Driven BR40 for 100 miles before switching to DI40, DT40, or FR50 so the next UOA results aren't skewed and so you're not mixing very different formulations together.

MrMoose

I was talking about Spectre's results there, Petza. Like I said, I'm not expecting a change to Driven to impact consumption here: anti-wear additive levels are not at all relevant to an engine that's already burning oil.

It's all guessing until root cause is found. If it's the AOS, well, that's an easy one. If it were leaking that much I'd assume it would be pretty obvious. Valve guides or worn rings, only thing that may help is a thicker viscosity. Bore scoring, well, you're kinda #$!%'d on that one.

No point in doing an oil flush as, again, wear additives aren't your issue at this point. Were it me I'd verify OVS function and – if that's not it – maybe try a thicker oil and then drive it and monitor consumption. You can do a UOA or scoping if you like to rule out bore scoring, but not clear that helps you that much given there's nothing you can do about that (basically it'll just let you know if you need to plan for a rebuild). So might as well change the oil, drive it, and see if a different brand or viscosity make a difference.

But please do make sure it's not the AOS first as that's a possible root cause and a simple fix. There's a crankcase vacuum test for the 9x7.2 cars, not sure how well that works. Can you pull the AOS hoses, any excessive oil in them or in the intake?