what is the best oil for this engine? mineral/syntetic? 5w30 or 10w40 ?

 

Personal preference i guess? I always ran non synthetic. 5w/30. I think the cap says 5w30 for the car so that would be why I used it.

But now I run straight 50W but its not exactly a daily driver application.

 

I live in a warm weather state, and I was told that since my car has 200K on it, I should be running 20w50.

So it depends on miles, and weather. I would think that up north 20w would turn to syrup in freezing temps

 

I've always been one to run whatever the manufacturer says to run. The cap says 5w30, they designed and built the engine, so that's what I would run. 58mark, where did that chart come from? I would imagine its not from our cars, since it talks about turbo engines.

 

it's a general chart to show the application of different oils in different temps

I believe the 5W recommendation is a CYA by GM to cover all people in all climates. And of course, they are speaking to people that have brand new engines during a break in period. (not exactly something most of us are dealing with around here)

 

Unless you're running a turbo or doing some serious high speed driving/racing (150 mph) I don't see the point in running 20W-50 or 10W-40. Phoenix in the summertime, I could see running 5W-40 or 10W-40. But for the average person here who is doing street driving with moderate corner carving in open traffic, just stick with 5W-30 or if you want 10W-30.

Even 5W-30 runs thick at startup during the summertime and pegs the oil pressure until the car is warmed up. So why run something even thicker that's going to send the pressure even higher? I want less wear at startup. Not more.

I run 5W-30 year round in Texas.

 

Something to remember about oil viscosity ratings that most people miss is that they're not necessarily the same.

0W-30, 5W-30, 10W-30, and 15W-30 all act the same way when the car is fully warmed up. They act as 30 weight oils..... The only difference is the cold start and how long it takes to thin the oil to 30 weight.

10W-30, 10W-40, and 10W-50 on the other hand act differently not only at fully warmed up. But act differently when cold as well. So in these cases the 10W-30 will be thinner than the 10W-40 which will be thinner than the 10W-50 when they're all cold.

It's this reason why a 5W-20 will be thinner than a 0W-40 at cold start.

Straight 0 weight will be thinner than 0W-30 when cold.
Straight 30 weight will be the same as 0W-30 when hot.

Those charts above are OK for comparison. But I don't think they're a good recommendation. Because there is a difference between the car starting vs the car operating well. The pour point of Mobil 1 5W-30 is -42°C. The pour point of Mobil 1 0W-30 is -50°. But if it's -38° outside, you'd still be better off with the 0W-30. Same thing with block heaters. People will say they can start their car at -35° without the block heater. But it will sound like a bucket of bolts. Better to use the block heater.

Now I know most of this has little to do with us. We almost all live in warmer climates and most of us don't drive our cars below freezing outside anyways. But the thin/thickness of oil is relative to all of us.

 

I'm in a warm climate. In my 2.8L, I've used Valvoline VR1 10w30, or other times, I've used VR1 20w50 mixed with cheaper 10w30.
Next time I'll use Quaker State Defy 10w30 mixed with Defy 10w40 (only mixing because I need to use up some leftover oil).

In the case of Defy, 10w40 has a higher ZDDP content than the 10w30 and other versions do. People disagree whether that matters, but I prefer the ZDDP closer to where it was when the engine was designed and built.
More generally speaking, as you move from 5w30 to 10w30 to 10w40 of any brand of oil, the HT/HS viscosity increases. My understanding is that HTHS is an important metric at points of extreme heat and stress (most pertinent to WOT abuse). Whether these differences matter is debatable, maybe it only matters on a race track, but it doesn't hurt.
Flip side of course is that when cold, 5w30 is better than 10w30 or 10w40. I'd worry more about that in a cold climate, and especially for people who don't wait for their engines to warm up before beating on them.

I'd select a hot viscosity based on your observation of hot oil pressure. According to 60degreev6.com it's supposed to be 30-55psi at 2000rpm. I don't know where they got that spec from though. Keep in mind that dashboard gauges aren't very accurate, so if you're really feeling bothered to measure it, it's better to hook up a mechanical gauge. I've seen huge discrepancies when doing that.
Pressure is regulated to a maximum, on my 2.8 it's limited to 60psi. You don't want it to be pegged under most circumstances - if it is, viscosity is too high.

Bottom line though, I wouldn't stress about it too much. The choice between 5w30 and 10w40 isn't going to blow anything up. My personal belief is that the long term effect these choices have is more subtle than people think. The most important thing is that it has something in it, that's always kept at the correct level and isn't so old it's turning to sludge.