Hello!

I'll soon be soon performing my second oil change and I'm debating what oil weight to use this time.

My car is a stock 97 Z28 with 43k miles that currently runs on 5w-40 Chevron Synthetic.

When I first bought the car it had regular 20w-50 dino oil that was put in at the dealership due to a minor oil leak (they eventually fixed the issue and I decided to put synthetic back in). Right now I have no leaks using de 40 weight Chevron synthetic, and the car has run fine for the past 3k miles.

I can get a great deal for 5qts of Mobile 1 Extended Performance 5w-30 synthetic on discount; trouble is I'll be missing around 1/2 a qt for a complete oil change.

At first I was just going to buy an extra qt of the same weight, but now I'm considering filling the rest with the same type of Mobil1 EP but in a 5w-50 weight.

That way I would achieve a slightly thicker overall mix.

From what I have gathered, according to the M1 website they seem to be able to safely combine (unless someone else knows better).

Has anybody successfully tried something like this before?

I keep reading all over the internet that plain M1 5w30 is too thin for our engines, however some of this posts are old and the formula has changed ever since.

From my research, it seems that viscosity has gone up from 10cSt @100º to 11.2 over the past 5 years (German Castrol which some use is 12.1 for comparison).

Extended Performance M1 also seems to have better additives and is better regarded in the oil forums than the traditional M1. Where I live, temperature is typically around 70º during the day, rarely below 32º or beyond 95º.

I don't normally race my car, but I do like to push it hard.

Is the new EP M1 5w-30 formula good enough or do you suggest I experiment with 1/2 quart of 5w-50 to be "more on the safe side"

PS. I have nothing against Chevron 5w-40 synth, but I can now get the Mobil1 EP for the same $, and much less than other brands some of you might suggest

Thanks for your help.

 

5w-30 is what the mfg recommends for the stock engine.
I run 10w-40 because my motor is completely built and has looser tolerances. There's also much more downward force on the pistons/rods, so thicker oil should help avoid metal to metal contact.

 

Wow, your concern and in depth of knowledge of your topic of concern is admirable. But be real, it's oil. Change it often, keep it clean, but a half a quart of a different weight aint gonna mean squat. You could use baby oil if you wanted and it wouldn't make a difference.

 

First I would NEVER run 50wt in a stock modern engine unless I was racing in the desert. And I'm not sure I would then. With your mileage the 5W30 should be fine.
And no, mixing small amounts of different oils will NOT hurt the engine.

 

I run moble 10w 40, just think 5w 30 is too thin, you will be fine with most weights its kinda up to you, i wouldnt run 50w or anything but you prolly could

 

Wow, what a thread!

Baby oil would be OK...obviously just trying to make a point but it's certainly not true LOL

5W-30 is too thin....certainly not true, it's what GM recommends.

There are a lot of threads out there on oil and one, in particular, is outstanding: www.bobstheoilguy.com . You'll learn a ton and be able to dismiss some misconceptions. For example, engine oil and gear oil, both SAE, are different scales...a 80W gear oil and a 20 engine oil have the same viscosity, about 75 centistokes at 100F...who'd have thought that.

I doubt it's a problem to add a half quart of the higher weight when you do this change. I wouldn't do it since I'm **** but it probably won't matter. Like some of the others, I wouldn't run anything heavier than 30 in the engine...it's just eating a little power by forcing the oil pump to work harder....

 

true... but thats for a new car, wear on the motor can be a reason to use a higher viscosity, also it get 100+F in OK all summer long so I prefer a thicker oil

 

of course..it's a personal choice..nothing wrong with that.

I guess I haven't ever seen the need to run thicker oil in my 120,000 mile Trans Am here in Florida. I still get great oil pressure even when it gets warm here.....

 

Thanks for all the input.

That does give me some peace of mind, have you run 5w-30 M1 since new?

Adding just 15% of 5w-50, as some of you mention, might not have a real noticeable impact - I just wanted to thicken things up just a bit. But from further research, it's now apparent to me that the end result cannot be predicted so I'll probably just stick to the basics

One thing that does concern me is that Extended Performance M1 lacks the GM 4718M (Corvette) spec.

Is this essential for LT1 Camaro's?

The '97 owners manual does not mention it.

 

I've only had the car since 2002 but the previous owner told me he used Mobil ! since new. I certainly have used it for the 60,000 miles I've had it for...

I can't help you on the specification question....sorry.