What oil is best for the 91 q?

[american v8]

So my brother just recently purchased a 1991 q45(1qikq45, I believe his user name is). Its his third q in the past few years. When we bought the car we found three quarts of Valvoline conventional 10w40 and a penzoil filter (still in the box) in the trunk. The oil in the engine is a dark brown, but not completely black yet, so it has about 1000more miles left before she needs to be changed. So my question is: Is the Valvoline 10w40 ok to run in these cars? I know I have to run a synthetic blend before I go full synthetic. But what oil would be best. In his other q45 he liked to run that Q oil. Should we do that? What oil makes the car last longer? Speaking of oil, we havent checked the transmission oil yet. What brand should we use? these cars are starting to grow on me, so I get to do the work in my auto class!

[Q45tech]

Selecting viscosity on oil is best done by measuring idle oil pressure in a high mileage used car.

The OEM minimum at idle is 14 psi.

Brand new oil with a new filter is the point where oil is the thinnest [thus lowest psi] since every mile of use allows evaporation of it's lightest components.

Synthetics are made from the same size molecules not a blend of small>large like convention, hydrocracked, or blended oils.

Thus a synthetic will hold it's brand new viscosity from 2-3 times longer in miles. See volitility index.

The most sensitive bearing are crankshaft, rods, and wrist pins...............without measuring them all you know is the clearances are wider [worn] than brand new.

Wider clearnaces show up as low oil pressure!

One selects oil viscosity to be with specifications [oil pressure] under the most extreme hottest temperature at lowest rpm.

IN DRIVE AT IDLE = 650 rpm.

Hook up an accurate oil pressure gauge and data log the psi vs coolant temperature thru warm up cycle. Then draw a graph

While Xw30 is new oem as the miles pile up it may be necessary to go up to 35, then 40, then 45.

My AMG C43 oem fill is 0w60 EU Mobil 1 BRAND NEW. BMW also uses this in performance models.

Unfortunately 0w40 is the only easy US Mobil product to find

Many PHD spend their entire life studying and blending oil.

Iwould read and follow the links here after 10,000 posts you might understand SOMEWHAT:http://www.bobistheoilguy.com/...age=1

[Skibane]

Mobil 1 works very well, both for engine oil and ATF.

For a California car, 10W40 is a pretty good choice, provided your Q's engine is healthy. The fact that Infiniti recommends a slightly thinner weight is due more to a need to meet CAFE fuel economy standards than to maximize engine life.

[american v8]

So, Basically, I should use a synthetic 10W40? But I've always heard that I should use a synthetic blend for at least one oil change before going full synthetic and if for some reason I need to go back to conventional, I have to run a synthetic blend again. So, what brand of synthetic blend should I use? Moblie 1, Q, penzoil, valvoline?

[Q45tech]

Since 250,000 miles [currently 325k], I've used conventional Valvoline 10w40 changed evey 90 days. because of low capacity oil filter and sump.

[qship96]

Why did you stop using synthetic changed every 90 days???