I have a 1978 Pace, L82 with 62,000 original miles. (no oil leaks by the way).

I have a question regarding the difference between various engine oil weights. The previous owner who sold me the car always ran 10W-40. Up until now I have always just stuck with 10W-40. However, a couple weeks back when I had my oil changed, the place no longer had 10W-40 available. They recommended a Kendell 20W-50 motor oil.

I am looking for someone to help me with my ignorance. What do the "numbers" in the oil weights really mean? What would be the difference for me running 10W-40 vs. 20W-50 in my, Southern Minnesota, climate? :confused:

Thanks for any insight! :cheers:

 

20/50 will be ok in the warmer months. But i bet it can get cold up there in the winter. In the colder months I would drop to 10/30. Its thinner and can flow better on cold starts. If you really want the best all climate protection, go with a brand name synthetic oil like Mobil1. Far better than any dino in most respects. Just costs more. But worth it if you plan on keepin yur car for a long time.

 

Looks like it's that time of year when everyone is changing their oil...good idea. I always change my oil when the season changes.

The numbers are there for comparison, there is no physical property associated with it directly. The number represents the oil viscosity which is a measure of how well it flows and has nothing to do with lubricating qualities, but is to some extent a measure of how well the oil will hold up under pressure like in rod and crank bearings. For example, a 30 weight oil is known to flow well at room temperature (72 degrees F), a 20 weight oil is thinner and flows easier, but at the same time will squirt out of rod bearings too soon and cause metal against metal contact which results in bearing wear and friction, while a 40 weight oil will be thicker, but may not flow as easily which could load up the oil pump and reduce the volume of oil that is being circulated. In addition to this, the thickness (viscosity) of the oil will change when it heats up and the oil will get thinner. Several decades ago we had only a few choices...20 weight, 30 weight, or 40 weight...the selection depended on what the lowest temperature would be during it's use...if it was not going to be below 40 degrees then 40 weight was selected. If it might get below 40, but not below 10 then 30 weight was selected...otherwise 20 weight was required so that the engine would have some lubrication while it heated up...or in more expensive machines the oil pan had a heater so that the thicker weights could be used to protect the engine after it got up into the operating range. I'd like to point out that a 50 weight oil was not used since it was way too thick in a cold engine to be pumped through it.

With this in mind technology developed oils which do not change as much when they are heated. Well, now that they had these better oils how do they inform the public? By the numbers! A 20W-50 indicates that at temperatures around 32 degrees F (The W indicates which number is for cold temperatures and is sometimes called the Winter number) the oil will flow like a 20 weight oil, but as the oil heats up to around 200 degrees F it will flow like a 50 weight oil. This is great! Cause when the engine is cold it will flow nicely and when it heats up it will still be thick enough to stay in the bearing caps!!!

Now, the only thing you need to consider is how cold it will get. The owners manual for my 75 lists the following:

For temperatures below 20 degrees F: 5W-20, 5W-30 but with a warning that the 5W-20 is not recommended for sustained high-speed driving, while 5W-30 IS recommended for Canadian vehicles, but I wouldn't risk it...if it's going to get this cold then go with a 5W-50 and get an oil pan warmer for when it drops down in the minus teens.

For temperatures between 0 and 60 degrees F: 10W, 5W-30, 10W-30, 10W-40

For temperatures above 20 degrees F: 20W-20, 10W-30, 10W-40, 20W-40, 20W-50

These numbers are SAE numbers and are still good today.

Also, lubricating qualities are not listed by a number of companies, but they may indicate the service rate which means how often the oil will need to be changed. There's two ways to determine lubricating qualities: 1. find an oil company that provides the specifications for their oil like Pennzoil, or 2. just rely on the popular brand. Personally, I use pennzoil; but, some of the other brand name oils have the specifications available as well.

Hope this helps.

 

thanks a lot rocknroll for the clarification.i posted earlier a similar question. :thumbs:

 

Here's the article that convinced me to go 5W-40 Shell Rottella T.
http://www.nightrider.com/biketech/oilinfo1.htm

 

Keep in mind that what was recommended in the owners manuals 25, 30, 40, or 50 years ago was based on the oil that was available at that time. Times, and oil, have sure changed since then.

With modern oils, the major wear occures at start up. That period of time from when the engine starts to crank over until the oil pump is able to get oil to the wear surfaces. To speed up that flow of oil you want something that is as light as possable, say a 5 or 10 weight. Once the engine gets going and is warmed up there is almost no wear while that engine is curising down the road. Then you need a good all around weight oil like a 30 weight. So what we have here is a 5w30 or a 10w30 oil.

With modern oils there is only two reasons to run a heavy oil. One would be a race/tow engine that opperates at high stress/temps for long period of time. The other would be for a highly worn engine that needs the thicker oil to fill in the gaps in the bearings.

Me? In my both my 73's, L82 and LSs4, my 90 coupe, and in my 2000 truck, I run 10w30 Mobil 1.

tom...


[Modified by Tom73, 10:27 PM 5/6/2003]

 

Great link, BS! After reading that, I think I'll continue to use Mobil 1! :D

JB