[vwalburn]

What's everyone's opinion on using a 10W-30 oil instead of 10W-40? Seems to be getting tougher to get 10W-40 of any brand. I only put 1K on my oil between oil changes and don't drive it hard, if that matters.

[Sirrotica]

FWIW, back in the 80s I worked in a buick dealership, and had access to see the GM tech bulletins. GM has recommended against using any brand of 10W-40 oil because of the additives problem with gumming up rings on the pistons. I quit using it then, and have continued to only us 10W-30 in my own, and customer vehicles.

I personally use mostly Pennzoil, and have had zero trouble in the last 40 plus years with their oils. On occasion I have used some Walmart full synthetic (Super Tech), but always stick with the 10W-30 weights in my cars, winter, or summer.

Pontiac originally recommended 5W-30 in the GTO LS engines, but later changed it to 10W-30, which is what I started using from the initial oil change when I bought it new.

From my experience, you'll be fine with 10W-30, and keeping oil clean is much more important than what weight, and brand, is in the engine.

[vwalburn]

Thanks for the advise! I should have mentioned that it'll be used in my '64 GTO but I think the advise is still good. 10W-30 will work fine in the old GOAT.

[Goatracer1]

I also use just 10-30 in all my old cars. One engine was rebuilt 24 years ago and it still works great. I worked for Pontiac in the 1970’s and by factory recommendations we used nothing but straight 20W20 motor oil in customer cars. The additives that make it a multi viscosity oil don’t last. The closer the viscosity range the better.

[b-man]

10W-30 either synthetic in my LS V8s or the same weight conventional oil in all my Pontiac V8s and air-cooled VWs has always been the oil I’ve used. Never had any oil related issues ever, even 5W-30 would be fine and I’ve used that as well.

[geeteeohguy]

10-30 was factory fill the original GTO's. I remember the 10-40 issues 40+ years ago. Forgot all about that! I've run 15/40 Rotella in all my flat tappet cars for the past 22 years with zero issues. I am in a very hot climate. I change my oil every 3000-4000 miles or 8 years, whichever comes first.

[Geoff]

I use 10W/60. It has exactly the same cold weather flow characteristics as 10W/XX oil, but does not thin out as much in the higher operating temps in very hot weather.

These old engines have larger bearings & looser bearing clearances than modern engines.

[Kenth]

To attain the relevent sae number the oil has to be at 100°C.

SAE 30 11cst approx
SAE 40 14cst approx
SAE 50 18cst approx

Centistokes (cst) is the measure of a fluid's resistance to flow (viscosity). It is calculated in terms of the time required for a standard quantity of fluid at a certain temperature to flow through a standard orifice. The higher the value, the more viscous the fluid.

As viscosity varies with temperature, the value is meaningless unless accompanied by the temperature at which it is measured. In the case of oils, viscosity is generally reported in centistokes (cst) and usually measured at 40degC and 100°C.

SAE 60 is in fact 24cst viscosity at 100°C!

This is 33% thicker than an sae 50, 70% thicker than an sae 40 and over 100% thicker than an sae 30!

So, what's the problem with this thickness?

Well, this is measured at 100°C and at lower temps (70-90degC) all oils are thicker than at 100°C so the problem is compounded to some extent.

The downsides of such a thick oil (when not specified) are as follows:

Additional friction, heat and wear.
A reduction of BHP at the wheels
Higher fuel consumption.

The 10w part is the cold start viscosity and it is the same regardless of the specified operating temperature viscosity, in case anyone thought otherwise.

FWIW

[Tom Vaught]

I would be interested to read about anyones experience (who have actually done Oil Testing in a controlled lab environment).

Post up if you have "been there - done that".

Examples of the testing would be Flash and Flame point of the oil for example.

Tom V.

[Geoff]

This quote comes from the Bosch Automotive Handbook, 3rd edition, 852 pages.
Page 223: ' A good multigrade oil extends through several SAE grades, eg SAE 10W-60'.

[Kenth]

True, but i would stop at 10w30 for a healthy classic GM V8, driven at normal engine temperatures.

Following the manufacturer's recommendation isn't that hard.

[Sirrotica]

10W-60 oil isn't at all common in the US, you'd have to order it if you wanted to use it in your car.

I've owned plenty examples of cars with the Stratostreak V8 in them in the last 50 plus years that I've rum 10W 30 oil in.....

When I owned my Pennzoil service station 1977-1982, I had capacity for one type of bulk oil, I always had 10W 30 weight for the bulk of my customers. I kept quarts of other oils for customers that wanted straight grades, racing oil, 20W 50, etc. Back then I specialized in servicing Pontiacs, and had many Pontiac owners as customers, both high performance cars, as well as daily drivers.

In 1970 I did my Co-Op time as a senior in high school in a Pontiac dealership on the grease rack. They had Pennzoil 10W 30 for their bulk oil for all the customer cars as well. In both cases from the dealership, and my own business, I saw no oil related failures in cars that were taken care of by the owners. I still use it in all my driver cars, no matter what's under the hood.

As I said much earlier, the viscosity, and oil brand is no where as important as keeping oil clean. Most anyone that has spent any time on this board knows I use a by pass oil filters, and endorse their use, along with the factory issue full flow filter. Two are much better than one. Twelve years using by pass filters, saves me money, and time, as well as extends engine life.

Anyone can certainly extend engine life by doing low mile oil changes with a conventional filter system, my father (mechanic for most of his adult life) changed his oil and filters at 1,000 miles as long as I can remember. I prefer using a better filter system in my own cars and trucks, and doing extended oil changes. Saves money, and time, as well as extends engine life.

I inherited my parents 99 Grand Prix, at just over 70,000 miles in 2018. It had oil changes every 1000 miles since they bought it in 2000. It's at 145,000 now and runs perfectly, and is clean inside of the engine. Two ways to arrive at the clean oil, clean engine goal. Clean oil though, is how to keep engines alive, and in good health.

[65madgoat]

Use any oil you want. Either will be just fine.

And drive it hard vwalburn. Ha.

[vwalburn]

Thanks for all the input! I've decided on using Valvoline Maxlife 10W-30. Considering it gets changed below 1000 miles, it should be fine.

[vertigto]

Might want to consider Valvoline VR1 10w30 for the high zinc content.

[gtopont]

Valvoline oil WITH ZINC ! is the proper way ...ONLY... I purchased my 65 gto New in hackensack nj blue and white pontiac dealer later in bogota nj simmons pontiac..when i went to the dealer s car show the owner noticed my window sticker that i taped on just for the car show..owner mr simmons asked main mechanis to come see my car that i purchased 40yrs prior 2005..offered to do anything i needed for free if i needed any work done ! anyways we all talked about the oil type and 30 weight or 10-30 with ZINC is the best oil to use..by the way i was 16 when i bought my 65 gto trapped muskrat saved the money and bought a mini bike and gto..only drove my gto once for 2 miles when 17 the it sat until i got home from vietnam in 1970 so now i have 43,093 miles on it..IRIS MIST 4 spd tri power black interior..i love it..

[gtopont]

Originally Posted by vertigto

Might want to consider Valvoline VR1 10w30 for the high zinc content.

YES !!!!!! this is the RIGHT way to go 30w WITH ZINC !!!!!...zinc zinc zinc

[vertigto]

Originally Posted by gtopont

...only drove my gto once for 2 miles when 17 the it sat until i got home from vietnam in 1970 so now i have 43,093 miles on it..IRIS MIST 4 spd tri power black interior..i love it..

Pics please!!