Tik

The manual recommends Mobil 1 15W-50 oil for track events. Do we really need to change back to 5W-30 for street driving? Any harm in just using 15W-50 as default?

jbondfl

It depends on how cold it gets in Redmond. 5w-30 is formulated for "all" weather. 15w-50 will work in all weather,,, you just need to be more careful about letting the car/oil warm up before jumping on the throttle.

Bill Dearborn

The manual says to change back to 5W30 once you return from the track. There could be a good reason for that. Average oil temps on track with a good driver pushing the car to the limit are probably 40 to 50 degrees higher than the temps seen on the street or highway. At street temps it might be best to have a 5W30 oil in the engine while at the higher track temps it might be best to have the 15W50 which will not thin out as much. I imagine even at street temps the 15W50 oil has a 50W viscosity which would might keep it from getting through some of the narrower passages in the engine.

Bill

6Speeder

They probably say change back because of better MPG with the thinner oil.

occar

I have been told by my service department that they have no concerns about leaving the different weight oil in it, but your mileage may vary (figuratively, and literally in this case).

thebishman

Only problem with that is if you have a major engine related warranty claim it's the regional rep you have to deal with, not the service dept. Not saying it will be an issue, just that it could be.

Personally I'd change back to the 5W-30 after tracking the car as the lower weight oil might protect better upon initial start-up regardless of the ambient temp.
Bish

Tik

Mobil 1 has a 5W-50 variant - apart from slightly lower fuel economy, why wouldn't this be a good middle ground?

rob3

Castrol makes a synthetic 10-60. You may have to go to a BMW dealer to get it, though (it's the recommended oil for the V10 m5/m6).

SouthernSon

To make the stretch over the characteristics of different grade classes the oil has modifiers added. These modifiers do nothing for lubricity. The greater the percentage of modifiers, the less percentage of actual oil. Thus, the reason engine builders prefer single grade oil in controlled circumstances. As far as Mobil 15-50, more ZDDP than their other grades, among other reasons for use.

therza

The Mobil 1 15W-50 does not meet the dexos 1 spec that is required for warranty purposes. The 5W-30 does meet the spec, hence the "need" to change it back after the track time.

And I have been told that the 15W-50 does indeed have more ZDDP which, over time can damage the catalytic converters. If nothing else, GM may not warranty the cats if you have issues with them and are using 15W-50 full time. Same probably goes for the engine as well.

And yes, it is the zone rep's call, not the service manager.

SouthernSon

It doesn't have that much ZDDP, only more than the other grades. Your speculation on warranty issues is, more than likely, unfounded.

MitchAlsup

A 5-W-30 (street) speced engine wants the oil to be at 10 centiStokes of viscosity +/- 2 and it will have that when the oil is between 190dF and 215dF. The engine will not be suffering "excessive" wear until the oil gets down to 2.5-3 centiStokes.

That engine being used at (road race) track power levels will be operating the 15W-50 oil at <presto> 10 centiStokes of viscosity when the oil is 280dF to 315dF. This is the perfect viscosity of the oil for the engine.

Note: the grade-weight of the oil is not what the engine was designed to use--what it is designed to use is the actual kinematic viscosity of the oil; measured in Stokes (where centi means 1/100).

Why change back while driving on the street?

Well that M1 15W-50 oil has 125cSt of viscosity at 40dF (starting temps) and over 700cSt at 0dF,
While that M1 5W-30 oil has 61cSt of viscosity at 40dF and under 280 at 0dF.

Secondly, after a day or two at the race tack, the engine has "consumed" the additive package of the oil--the antiwear protective parts at least. The filter will be partially partially clogged with debris, the oil viscosity improvers may have sheared to the edge of the grade-weight,..... So, you want to refresh the additive package, and changing the oil is a good way to get this done.

Remember the engine wants 10cSt at all points in time, freezing, clod, hot, race track temps. No one oil grade-weight is optimal at anything but over a small range of temperatures.

descartesfool

In my Z51 I changed out from the 5W30 to Mobil1 15W50 for the track, Changing back and forth is a pain, and I don't buy that the additive package is consumed after a day or two at the track.

For my GT-R which I have had since 2008 and been beating hard on the track for 6 years, there is only one factory recommended oil type and viscosity for both street and track and that is Mobil1 0W40. There is no requirement from the factory to change it out after one or two track days, and I just change it out after 3000 miles if I have been doing a lot of track days on it. Engine is still running like a top, and oil was sent to Blackstone after lots of track driving and there were no issues with the report. I wonder why GM did not design the engine around Mobil1 0W40 and not have owners who track the Corvette deal with the bother of changing the oil in and out. Porsches run on Mobil1 0W40 like my GT-R, and you can beat on Porsches all day on track. No different oil required on Porsches for track use, just like the GT-R. Mobil1 0W40 is one of the best oils that Exxon makes. Since engine wear occurs mostly at startup, using a 0W spec will provide the most flow into the bearings when the car is started from cold. I can only assume GM is recommending 5W30 which meets Dexos spec as a marketing tool since Dexos is their own spec, and I believe any oil manufacturer that puts Dexos on its oil has to pay GM a royalty.

And about starting temps, I virtually never run my track cars at 40 F. Stingray like the others is in the garage waiting for warm temps. For anyone running their cars at cold temps, it certainly makes sense to change back to 5W30 from 15W50, but if you start the car in warm temps, then not so much.

SouthernSon

Thus we have actual observed vs. theory. I, too, have run hard track miles for 10 years or so. Let the oil come up to temperature and let her romp. Might get a little better perspective from aviation oil. No harsher environment seen by any engine. From the freezing high altitudes, to cold start ups in Alaska to the hot equatorial zones most planes run single grade. Even engine break-in procedure is tow plane out to end of runway, get clearance before firing up the engine, upon start up go full throttle and circle airport for an hour or so at low altitude and full throttle. Seriously!

http://www.shell.com/global/products...s-w80plus.html

Foxer55

This discussion is all well and good but I don't think it gets to the OP's reason for the question. If you change the oil for every track event and then change it back, things get costly real quick. As an example, if you track the car just 4 times a year that means you need to change the oil 8 times. 8 times at $80/change means you're spending $640 a year n just oil changes.

dvandentop

i have ran 15w50 on the street no problems in my c6z

Tik

Thanks, Foxer. Cost is certainly one of the reasons I'm asking, but so is practicality. It seems needlessly excessive to have to swap back and forth between different oil weights between driving on track and on street. I've been driving on the track for years (am an instructor with numerous clubs) and this car will see the track at least once ever other week once the season gets going. Previous cars I've driven called for one oil weight for all purposes (BMW M cars use 10W-60, P-cars use 0W-40, as highlighted earlier, etc.). This is the first car I've owned that suggests different weights for street and track - it's perplexing and doesn't seem at all practical. I think what I'll end up doing is switch to 15W-50 at the beginning of the season, run that on street and track until the end of the season (changing as needed based on total driving time), then switch back to 5W-30 at the end of the season.

Really wish we could just run 0W-40, as I agree that's a pretty bomber oil...

lt1z

The 15w50 will work with higher oil temps on the track in V8 mode but will not work well in V4 mode which is why the recommend switching back for regular driving.

thebishman

As previously mentioned, I believe that the 5W-30 is to mitigate first morning start-up wear especially in cold/cool weather, but having to switch to the 15W-50 is to help protect the engine in high stress events such as an HPDE. Furthermore, have you looked at the oil when its been freshly changed prior to and then after a three day track event? The oil turns black very quickly and goes to show the huge heat stress placed on it. In fact it could well be that the modifiers specific to the higher performance oil have been partially consumed. (I used Castrol Motorsports TWS 10W-60 in my '09 GT-R which I believe to be one of the best oils made for high stress use, but even it looked like crap after one event).

YMMV, but changing the oil after a high stress event like an HPDE is just extra insurance, and frankly given what you'll spend on tyres over the course of a track season, $680 for oil changes is nothing IMHO.
Bish

zeshawn

the funny thing about viscosity ratings is that the Mobil 1 0w-40 is less viscous at 100degree Celcius vs the Mobil 1 5w-30 based on the information from Mobil1's website. Ive had good experience with Valvoline VR1 oils however your catalytic converters will not like it.