DallasLoneStar

Title pretty much says it all. Which weight should I be using? Still stock or a little heavier? Appreciate all the knowledge on this forum.

This is for a 2003 Z06 if that matters.

Vetteman Jack

I have always run 5W-30 weight oil - lived in TX for four years and did not have any problems with the car.

Supercharged111

Stock.

jackthelad

Unless your idle oil pressure gets too low when hot, stick with stock 5-30. You could try 10-40, it won't do any harm, but probably not much benefit either. Mobil does a High Mileage full syn 10-40 if you are interested.

DallasLoneStar

Thanks guys. What is a hot idle oil pressure where I should think about going thicker?

I do plan on light track / HDPE in the car, if that changes anything.

grinder11

I'd go with Mobil 1 0w-40. Or as others have recommended, 5w-30/stock fill. If you're over 20-25lbs@idle, and over 40lbs just cruising down the freeway@65-70mph, you're fine.

SkyTigress

Not a Vette, but when I lived in TX my 350z ate waaaaaay less oil on Mobil High Mileage Syn vs all other brands I tried (Amsoil, Motul, Castrol, LiquiMoly, Royal Purple, etc)
You should ask the dudes at Vorshlag in Plano what they run and any advice on small oil coolers since they LS swap everything and do track events (they drive Vettes too).

Kubs

The rule of thumb is 10psi for every 1000rpm. Based on that, if the hot idle pressure is below 8psi you should consider going up. I also do track and time trial events and I use 40weight oil for the extra pressure when hot. Sometimes the car sees 280° oil temps even with an aftermarket cooler, but I am also revving to 7200 rpm. The extra RPM adds a lot of heat.

MWWarlord

I'd stay with Mobil 1 5W-30 unless you're having issues.

DallasLoneStar

Thanks guys. Going to stick with synthetic 5w30. Was probably overthinking it.

wydopnthrtl

In my 04 w/42k miles I run 100% 5W-30 M1 and change once a yr (3-4k miles)

On older cars I run M1 high mileage at stock specs but I run about 25% of the capacity at a +1 viscosity.
ONE thing to note though.. if a car has variable valve timing I don't do that. VVT and I stick to stock specs as those very small oil passages can starve bearings / journals at cold start.

Justin Raney

So 5w-30 is best? I read somewhere 40wt was harder on the oil pump and orifices and could cause premature bearing wear as a thicker oil but that was what i was reading on a 300k mile corvette ls1 survival article. So unless oil pressure is low use 5w30 if not run 10w40 with 10-15 psi idle pressure. My car idles 20psi with the oil completely hot or a long drive 15-20 minute drives usually is 27 psi hot idle. Is there any reason not to run quaker state 10w30 5w30 full synthetic oil? Not to thread hijack i just have the same question as in texas it gets to 100 degrees in the summer sometimes 107.
And for oil changes to completely empty out the oil the rear needs to be raised on a jack slightly higher then the front oil pan to run out the oil from the back of the pan?

acroy

I run M1 0w40 in everything including the lawnmower. Slightly thinner on startup, which is a good thing, slightly thicker when hot, not a bad thing. A bit more zinc etc, still cheap. Hundreds of thousands of miles across multiple cars. Engines stay spotless inside.

walleyejack

i do the 0 w 40 amsoil thing, lots of zinc, doesnt get about 85 here in the summer usually.

grinder11

With today's oils, I'd never run 10w-40 in anything I own. Some of the highest power dyno results are with 0w-20. That's dyno only, of course. My point is, thick oil runs hotter, and costs power. I'd never run 0w-20 in anything, unless I lived at the North pole!!! IMHO, a 0w-40 is the way to go. Cold flow is almost identical to 5w-30, but has a bit higher viscosity when hot, and better high rpm protection. I've been running the 0w-40 oil so long, it was only available in quarts back then. Glad Mobil 1 sells it in 5qt jugs now!!! I usually buy 3, then I have enough for the Vette, and wife's CTS, with some left for the lawn tractor, and an extra quart for whichever car may need it. It's good stuff.......

strand rider

Let me put it simply, if you were hiring a helicopter ride in Texas, would you prefer the service be done strictly by the book, or is some guy saying I always like this other viscosity lubrication, with no problems so far, be good enough.

for stock needs, the owners manual covers it, along with track instructions if memory serves. There are so many uninformed opinions on this subject, or good information applied incorrectly, that I might sound preachy on the subject. Because the entire deal is designed as a system, you start changing parts in a system, and it is very easy to take the system outside of the designed system performance, and it is a lubrication system, not just some oil passages and a pump, like the old days.

I used to be a sailor, and sometimes would hang with the engineers in my off hours. These guys were well paid licensed engineers and highly experienced men, with three billion dollar responsibilities on some supertankers , and they didn't make crap up. They had the operating manuals all around the walls of the foc'sole and followed the operating instructions to the letter. Many of the guys probably had the education and intelligence to write their own operating instructions since they knew the systems so well, but there was no need, and it would create a possible legal exposure, and no sailor wants to burn shore time going to court.

I once talked to guy with and old curved dash Oldsmobile that steered with a tiller and had a total loss oiling system, it didn't recirculate the oil, and left a thin trail on the ground behind it. One has to get with the times and the LS1 in the corvette application had supercomputer hours invested in system designs. But lots of guys are happy to wing it, and I am happy too, as long as I don't buy a used car from them.

the main concern with oil is not heat, but dirt. right now the top of line purolater synthetic extra guard , or whatever it is called, is testing best, but you should know what you are doing whenever you step outside of the designed for system parts. I have heard stories of guy carelessly buying an oil filter designed for the old three thousand mile oil changes, run it longer, and then cry that the oil filter was pure junk when it let go and clogged up the oil passages in the engine.

walleyejack

Everyone has an opinion tho.

grinder11

Yes, I agree, and oil today is much different (should be better) than it was in 1995-1996, which is about the time the original LS1 engine was nearing final design. I'm not even sure that Mobil 1 0w-40 was available nearly 30 years ago. I know it was in 2004-2005, but only in quart containers. I agree the manual has it covered pretty well.....For a stock LS1. There are a lot of modified engines in the C5 membership here. I believe 0w-40 is a very good oil for the modded ones. My .02........

walleyejack

I concur