When and how have you personally deviated from the car owners manual


Jul 7, 2015
Down Under
I have 2006 Holden (Opel) Astra and the owners manual says to use 10W30 or 15W40 in ACEA A3/B3 or A3/B4. That's it. No other viscosity is listed, and no other standards like API are listed.

First oil I ran was Valvoline DuraBlend 10W40 A3/B4 semi-synthetic, close enough. Followed by other name brand A3/B4 10W40s as they are cheap and plentiful here.

I also ran some full synthetic A3/B4 oils such as Castrol Magnatec 5W30, Shell Helix Ultra 5W40, and Valvoline SynPower 0W40. Still no great risk, as they still carried the correct Euro spec, even if a slightly different viscosity grade, mostly the winter rating - which is nothing in my hot climate.

Probably my biggest deviation was Mobil 1 5W30, which was a ILSAC GF-5 and Dexos1 oil, so completely off grade and off spec. But hey, years down the road, and I'm still driving the car.
5w-30 and 0w-40 in a 2013 F150 specified 5w-20.

5w-40 in a Ford ecoboost specified 5w-30.

5w-20 and 5w-30 in a '15 4Runner specified 0w-20.

No loss of mpg or power that I could discern, and the UOAs performed were very good.

Other fluids: Amsoil, Valvoline and Schaeffer lubes/ATF used rather than specified fluids.

Tire rotation: frequently.
mainly just intervals. every 50k is a major service. every fluid in the vehicle gets changed. beyond that i use what it says.
vw calls for 502.00 specification for the mk6 2.0 I believe and same with the 2.5 when I had one,
both ran on 15w40 lol.

Power steering fluid was prestone universal
coolant was oem equivalent
atf was universal castrol lol.
Im running PP Euro L in my F150 Ecoboost right now. I also do 5k mile OCI’s because I genuinely believe it helps mitigate timing chain stretch and because it gets flogged towing a travel trailer in UT and the surrounding states

Im running M1 EP 10W-30 in my Lexus GX instead of 0W-20. It also gets used to tow my trailer.
Mazda recommended 30,000-mile intervals for repacking the wheel bearings in my Mazda. In over 600k miles, I never did it for 3 of the wheels, and never had any problem with the bearings. The left front was another story, due to water intrusion.
The owner's manual in my Mitsubishi has about 30 pages dedicated to using the Navigation system. Since new the unit has had outdated maps so I have deviated from it frequently. Plus mirrors have some annoying distortion;

I've been running 10w40 in all my engines spec'd for 5w20/5w30 for the past 30 years with no problems. One engine had 518K miles when the car was retired. Two of my current cars are in access of 200K miles and both use approximately a quart of oil every 5K miles. I'm running 7500 mile OCI's instead of the recommended 5K. This isn't owners manual related but I also exceed EPA fuel mileage estimates on all my cars by several MPG.
"Thick vs. Thin" thread in disguise........
Or is it? I'm a thicky and in my opening post, I never went thicker than the owners manual, but I did go thinner when I ran an ILSAC grade without problems.

Other posters have gone the other way, and gone thicker than the owners manual. Others are talking about OCI and not viscosity.

Looks like all are welcome here. It's a friendly thread.
What owners manual?
The only time I have ever looked at the owners manual is when I am looking for something else in the glove box...or when setting the radio's stations..

I bought a new van in 2002 and sold it in 2018. Never knew there was one until I cleaned it out for sale 16 years later.

That's not a brag...probably shoulda read it but when I saw 5-20 for oil on the cap I figured the manual was screwy also.
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My favorite way to deviate is to go against manufacturer instruction and make sure my car lasts as long as possible by changing fluid in everything. Transmission, Ford PTUs, you know, the things that definitely do just fine without maintenance. Least favorite is the battle of the tires, if I don't need a 125 load index, let me have my 121s.
I use 5-30 in my engines that call for 5-20. I change oil sooner than they say. I set my tire pressure a bit different. I change out my lifetime tranny fluid. And probably other things I am too tired to think about right now.