"Hey any idea why I don't burn oil in the wintertime?"

"Flynorcal: pilot, offshore sailor, car racer and panty thief" (flynorcal)
11/16/2016 at 19:09 • Filed to: None

I had lunch with a BMW mechanic and asked him that question. The answer was a surprise.

My engine burns oil. It’s a V10 and there’s a lot going on in there and a lot of pressure. It’s common knowledge that you keep an extra quart of 10W-60 around as every two months you’ll need it. I assumed the more I mash the gas pedal the more oil it’ll consume but I have noticed I haven needed any lately. I ran 7 autocross laps full-out last Saturday and didn’t lose any. (It’s measured electronically to the 1/10th and it has a delay between checks that would have hit by now.) I also have taken it out on the mountain roads a bit and let it off the leash and still nothing. It’s full and staying full.

In June it was drinking oil on the regular.

Last December I didn’t lose a drop.

That’s the pattern.

Rather than give you the answer he gave me I’m going to leave this out there for folks to ponder. Many of us are on our commute home or about to be so it’ll give you something to noodle on, and I’ll post the answer I got from my mechanic friend in a few hours.

Not that it matters but I’m in CA, use 91 octane all year (93 is what BMW recommends) aside from when I might get 100 octane at a track or outside of CA. I also have the same driving habits all year.

DISCUSSION (13)

TheTurbochargedSquirrel > Flynorcal: pilot, offshore sailor, car racer and panty thief
11/16/2016 at 19:14

Engine runs on a different tune when it is cold resulting in less oil burnt?

Garrett Davis > Flynorcal: pilot, offshore sailor, car racer and panty thief
11/16/2016 at 19:17

“Rather than give you the answer he gave me I’m going to leave this out there for folks to ponder.”

You’re a dirty tease.

aberson Bresident of the FullyAssed Committe > Flynorcal: pilot, offshore sailor, car racer and panty thief
11/16/2016 at 19:31

because you shift yourself

e36Jeff now drives a ZHP > Flynorcal: pilot, offshore sailor, car racer and panty thief
11/16/2016 at 19:31

perhaps the air-oil separator works better at lower external temps?

Decay buys too many beaters > Flynorcal: pilot, offshore sailor, car racer and panty thief
11/16/2016 at 19:45

Oil stays thicker in cold temps (assume an M5 would have an air oil cooler?) Hotter oil in the summer time can more easily bypass the oil rings and burn in the combustion chamber?

Maxima Speed > Decay buys too many beaters
11/16/2016 at 19:48

This my 97 Nissan with leaky main engine seals was the same way. The solution was use slightly thicker oil in the summer.

Edit: btw not recommending it I just did it because it was thicker than recommended oil or increase my chance of lung cancer breathing in burning oil pouring onto the manifold.

Flynorcal: pilot, offshore sailor, car racer and panty thief > Decay buys too many beaters
11/16/2016 at 20:39

Alas, I neglected to add this detail: I always let my car warm up to at least 130 degrees before moving it. I put the “I’m in California” bit in as a clue to it not being the weather. Great guess though.

Decay buys too many beaters > Flynorcal: pilot, offshore sailor, car racer and panty thief
11/16/2016 at 20:51

Ok stupid guess time!

The extra butane in winter blend causes knock and more blow by leading to fuel dilution in the oil. You’re still losing oil but the lost volume is made up by fuel

BMW programmed it in as a way to make owners frequent the dealer, it shuts down the program in the winter as a “Christmas present”

The oil level gauge is European and annually takes a few solid months of vacation.

Gremlins

Flynorcal: pilot, offshore sailor, car racer and panty thief > Flynorcal: pilot, offshore sailor, car racer and panty thief
11/16/2016 at 20:56

ANSWER: ...or at least the answer I was given anyway is that is has to do with the fuel. Winter blend vs Summer blend. With that change the fuel burns differently and essentially has a different knock point and the ECU adjusts spark accordingly. In the summer the gas has a bit more punch and will rattle the pistons back down the cylinders whereas in the winter the fuel burns a bit more slowly and evenly — much like a higher octane gas, which my car prefers — pushing the pistons differently and combusting at a slightly different part of the stroke where less oil goes past the rings.

I mulled this over for a while and realized that my car burns much less to no oil when running on higher ocatane gas as well. Outside of CA or if I get 100 octane at the track, the oil level similarly doesn’t drop.

Kind of a neat answer. How accurate is it? Well it’s all anecdotal but it seems to match up with what I’m seeing and he rattled it off the top of his head so it’s something he clearly has thought about before.

I thought it neat enough to share anyway.

Flynorcal: pilot, offshore sailor, car racer and panty thief > Decay buys too many beaters
11/16/2016 at 21:18

You guessed it as I was writing the answer except less knock so less blow by in the winter. Winner winner chicken dinner!

gogmorgo - rowing gears in a Grand Cherokee > Decay buys too many beaters
11/16/2016 at 22:55

Ambient temperature doesn’t affect the internal temperature of the engine (and therefore the oil) much. And if it does, your thermostat isn’t working correctly.

Decay buys too many beaters > gogmorgo - rowing gears in a Grand Cherokee
11/16/2016 at 23:13

Depends, not the case on most cars with air oil coolers. Many oil thermostats have a pretty excessive bypass flow (most I’ve tested are in the 20% range fully closed) in cold areas this can keep oil significantly cooler. On my FR-S for example, I’ll see 30C cooler oil temps winter vs summer (coolant rock solid in all seasons) and need to block my oil cooler core to hit 200c (sump temperature)

Water oil coolers do not suffer from this but generally run out of capacity before air to oil.

gogmorgo - rowing gears in a Grand Cherokee > Decay buys too many beaters
11/17/2016 at 08:22

/me has never owned a vehicle with an oil cooler. That would definitely reduce oil temp.