Question about Dexos

alvocado · December 14, 2023

Isn't this the same topic as your separate post from Sept 2022 running parallel in the replies?

Jworks · January 15, 2024

Well I have this to say, and I'll probably get some rebuttals and thats ok. I had sometimes noticed the engine "tick, tick" for a few minutes after I started it from cold. Then it'd go away as the engine warmed. I'd had all my oil changes at the dealer using the synthetic dexos1 oil they furnish which was I assume was ACdelco dexos1 and their basic filter they furnish. The last change I went to an independent and told him to put in Castrol s synthetic dexos1 and I wanted synthetic designed filter even if it costs more. The tick is gone -- even if it sits there a few days.

diyer2 · January 15, 2024

Dealer bulk oil I wouldn't use.

MaverickZ71 · January 24, 2024

Current GM light duty V8 engine oil spec is synthetic 0W-20. That's thinner than the tolerances in your (5W-30 semi-synthetic spec) engine were built for. That, along with extended service intervals, can contribute to the tick-tick.

Keep in mind that dealers do not usually stock bulk oil (in barrels) in multiple viscosities. My GM Tech at my local dealer laughed at me 20 years ago when I was requesting 10W-40 conventional, 5W-30 synthetic, etc on the work orders. You get whatever bulk oil from a barrel they are currently pumping from--today's vintage is 0W-20 "full-synthetic", the cheapest they could buy. I used to cringe when a friend of the family took his Z06 Corvette in for service.

Grumpy Bear · January 25, 2024

3 hours ago, MaverickZ71 said:

Current GM light duty V8 engine oil spec is synthetic 0W-20. That's thinner than the tolerances in your (5W-30 semi-synthetic spec) engine were built for.

Not picking on you Bret It's a common idea.

Piston to wall CLEARENCE is say .02" with a TOLERANCE of =/- .0025. Oil isn't spec'd on a tolerance or even on the clearance which can vary wildly within the motor. In a perfect world oil is chosen to fit the "Surface Roughness". The height and depth of the peaks and valleys. And for the expected parameters of the Stribeck Curve. That is a film thickness based on speed, load and viscosity that is thicker than the difference between the highest highs TO lowest lows. Purpose is to prevent surface to surface contact.

This is not totally possible in all regimes and/or operating conditions. Thus, the AW and EP packages.

The X axis of Stribeck where n = dynamic viscosity, N = Speed and P = Load. The Y axis is friction coefficient.

n then is dependent on chemistry AND TEMPERATURE. Why a higher SAE oil is specified for Track Day and/or Towing.

Did I say that? :crackup: SHOULD be specified for TOWING.

Ring to wall area gives the widest possible variation of conditions and the roughest surface finish thus the area the oil SAE Grade is specified for.

That is the perfect world. The REAL world the EPA gets a say and they say the lower the HTSH number the better regardless of reliability, durability and wear life.