Oil viscosity in V V T engines

[JimD]

These PDF files are too large to upload here and Photobucket will not accept PDF. Probably worthy of two different topic titles (Bruce?).

Two items of interest on this page as of 8/22/06. Under Recently Added Resources, "Repair Care VVT.PDF".

And under Recent News, 8/15/2006; "GM bulletin advises of normal...."

http://www.obdclearinghouse.com/

[Bruce Nunnally]

Variable Valve Timing Codes? It Could Be the Oil!

If all other components of a variable valve timing (V V T) system seem to be functioning

properly and the OBD codes will not go away, check to see if the oil has been changed

recently and if the proper grade of oil was used. Different grades of oil might look the

same, in the bottle, but do not act the same in the engine.

Vehicle oil must meet two criteria: It should be the proper Society of Automotive

Engineers (SAE) grade and viscosity and it should meet the American Petroleum

Institute (API) service classification for the vehicle. Both the SAE and API designations

can be found on the vehicle's oil fill cap or in the owner's manual.

The viscosity and grade of motor oil is what interests us here. Viscosity refers to how

easily oil flows. Two primary factors affect oil's viscosity: temperature and age. When

oil is hot, it flows quickly. Oil flows slower as it cools. As oil ages, the polymer additives

break down and the oil loses viscosity. The ability to flow smoothly in an engine is

important because most of the passages are tiny.

Most vehicles require multi-grade motor oil. This means the oil has characteristics of

both cold weather oil and warm weather oil. As an example, consider a vehicle that

requires a 5W30 grade of motor oil. This means that the oil has the flow properties of

a 5-weight oil when cold and a flow property of a 30-weight oil when warm. The "W"

means that the oil has been tested for cold weather use.

With more vehicle manufacturers employing variable valve timing systems on vehicles

to meet emissions and horsepower needs, how well oil flows through an engine

becomes very important. Many manufacturers use oil pressure or flow as the power

source to adjust the timing. If the wrong grade of oil is used or if the oil is old, the

flow properties could be insufficient. If this happens, the timing system will not work

properly and the OBD system may set codes.

[GreenMachine]

Very important information, really important for the newere members with the VVT engines, but intresting, especially this sentance for the rest of us:

"As an example, consider a vehicle that requires a 5W30 grade of motor oil. This means that the oil has the flow properties of a 5-weight oil when cold and a flow property of a 30-weight oil when warm."

I think this also may answer our long debate of 10w-30 versus 5w-30 in the Pre-2000 northstars. When warm, the differance is marginal if any (we all agree on that) and at startup is when the true test occurs (and sheering and this is where we get mixed results), especcially for us guys who need to get the baby cranking when stored outside in below zero weather, that 5w-30 will pour much better than the 10w in the cold weather, and the 5w is probibly not quite right at startup in the summer. Intresting when you think about it because our manusal even show that "gray area" where the two would overlap in performance.

Of course I'm speaking in Buffalo, NY terms of winter/summer where january has many below, at, or near zero days, and july-august has a few 90 days with the high 80s filling in around them, and on those rainy days 70's with humidity that will cause your glasses to fog up coming outside form air conditioning.