Engine oil Castrol or OEM Mazda

Vw recommends Castrol I wouldn't use anything else

They should be using 0W20 full synthetic oil (not synblend crap). Its not going to hurt running the 5W20 in it instead but next time mention it at write up. Mazda claims benefits such as better cold start protection and better efficiency among other things.

Castrol Syntec 5w40 is stout enough for the 10,000 mile oil change.

I've used the OE spec Castrol syntec 5w40 since I bought the car brand new. Do my own oil changes every 5k with the stuff and no issues.

I bought a liter of 507 (don't use anything else) Castrol SLX, and 15K later... still haven't broken the seal or had the level go below full.

Castrol EDGE Professional LL03 5W30 Engine Oil. Meets VW spec 507 and is what VW recommends.

I am also running castrol gtx 10w40 regular oil with the Lucas oil stabilizer on my vr. I had some light smoking issues before while running synthetic and switched over and it completely stopped.

I did notice lifter noise with the 5w-40 so decided to go with Castrol Syntec 10w-40 and it made quite a bit of difference in quieting down the lifters. I use a Mann filter. After i get the engine flushed on my VR swap using ****ty conventional oil, i'm going to run Castrol Syntec 10w-40 in it as well. Lots of people recommend 5w-40 or 0w-40 for the VR but i've found 10w-40 works well and my oil temps seldom exceed 208*.

On all these cars I have only used one method and found that the vr6 runs the best and smoothest on castrol gtx 10w40 regular oil with an addition of one litre of Lucas oil stabilizer lubricant every 2nd oil change. I absolutely love Lucas oil stabilizer treatment for my vr6s. It is such a thick lubricant that it comes out like honey and you have to squeeze it out. I swear I can tell a difference every time I use it. In any case, back to my personal theory, I have also had throughout the years experienced long time vw technicians tell me that the vr6 12 valve motor runs optimal on regular oil. They explained to me that the vr6 motor runs optimal when using thicker grades of regular oil compared to the less thicker blends of synthetic. I have even heard some people using diesel oil for their vr6. Apparently, the vr6 likes higher viscosity type oils because they don't breakdown as easily from the heat. The vr6 likes to run hot, more then most v6, and needs a thicker oil to lubricate against breakdowns. Synthetic oils can deal with heat breakdown well too, but I just think at the end of the day it does not compare. I don't know but I have noticed a difference. The current car I have now, mk2 gti golf vr6, was apparently running full synthetic before I swapped the motor in my car. So I did a engine flush and refilled it will my personal blend of castrol gtx 10w40 regular oil with the Lucas oil stabilizer and the car ran way better. Less engine noises, smoother idling, etc.

German Castrol 0W-30 is group 4 Oil and is superior to all oils mentioned above. If you look at bottle it says made in germany, not new jersey like other castrol oils. I have used since 15K miles now over 50K miles and zero cam follower wear, no gunk on intake valves, and minimal consumption..