Why is 10W40 Oil So Popular

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May 27, 2002
London, AR
I have not used this oil in 20 years. If I feel a need to use a 40W oil I will use 15W40 or 5W40. For 2 years I have watched post after post talking about using 10W40. What am I missing?

I guess about 5 or 10 on the W side...

Old habits. But I'm sorta with you.

In theory a 5W-40 would require a better designed oil and basestock than a 10W......

OK here's my real answer. They make 10W-40 petro oil. Haven't seen a 5W-40 petro.

As for the 15W....I guess a few people live in Minnesota.
I think 10-40w provides better protection when the engine is cold. I would use a 20-50w when I think an engine could handle it.
The thicker is better mentality is alive and well. The last time I used 10w-40 was in an 89 Honda Accord that was sold 5 years ago. The old Honda hated the 20w-50 even then since it started the tighter valve clearance over 15 years ago. Before that I used 20w-50 in an old Mazda GLC/323 sold 10 years ago.

When I bought a 94 Nissan Altima, I went with the 10w-30 and have been happy ever since. It allows for 10w-40 and 20w-50 over 50 deg F.

If the average joe started doing UOAs and seeing the shearing of the 10w-40 versus 10w-30 and 15w-40, he would probaly change his tune.
I'd say a lot of the popularity of 10w40 is from hand-me-down thinking. It was very popular and even recommended many years ago and that has been passed down from parent to child.
Seems to me that a 10w40 dino is no worse than running a 5w30 dino. Both have pretty big spreads.

I switched to 40 weight in my pickup (oil pressure was a bit low with 30 weight) and so far have run 10w40 and 15w40. May try 5w40 for next winter. My other two vehicles (wife's actually) are both run on 10w30.
You cant get 5W40 in Dino oil. I heard the closer the numbers are the less additive the oil has. It requires a lot of additive to make 5W40 Dino oil.

I have been using 10W40 Dino oil in my VWs for years. My dad also uses the same oil in his VW.
Beats me. My 1996 Volvo owners manual specifically says NOT to use 10W-40. 10W-30 or 15W-40 are recommended for summer weather conditions.

As others have said, for non synthetic the only choice is 10w or 15w. Since I change my oil at 3k and it doesn't get that hot...I use 10w40.

Originally posted by kickster:
You cant get 5W40 in Dino oil. I heard the closer the numbers are the less additive the oil has. It requires a lot of additive to make 5W40 Dino oil.

I have been using 10W40 Dino oil in my VWs for years. My dad also uses the same oil in his VW.

Same here. If you look at the 80's VW/Audi owners manuals, you'll see if you live in a climate that gets up to 90-100F in summer, 10W-40 is the choice according to the chart. 10W-30 only is recommended up to 60 or 70F on the chart.
And ditto. My new Kia Sedona (Hyundai's 3.5L V6?) viscosity recommendation for areas like mine, >95 degrees F., is both a 10W-40, and a 10W-50. (Is there a dino 10W-50?). Their chart absolutely does not encourage the 5W-20 because it is only acceptable up to about 40 degrees F. The ever popular 5W-30 isn't acceptable for any hot summer climates, as well. Even a 10W-30 is not recommended at temperatures over approx. 95 F.

I'm using the SuperTech full "faux syn" 10W-30, and I'll switch it to the Amsoil 10W-30 PAO, but if I went dino, looks like a 10W-40 for this engine.
Hey, it was good enough for Arnie's grandpa, must be good enough for me!!

Surprisingly, I still sell a bit, though not much.
Have a few customers who buy it for use in their diesels (been using it for over 20 years and not about to experiment with something new).
For years the viscosity improvers needed to make the 10-40 spread caused terrible sludge in engines. GM threatened to cancel warranty coverage for engines using 10w-40 at one time. On our LR (recommends 10w-40) the engine was completely sludged and I have only recently cleaned it up.

There may have been improvements in the oil technology since, but I would stay away from it. Use 15w-40 or 20w-50 if you must use the thick stuff.

The thicker is better mentality is alive and well.

I used to not be crippled by this affliction ..until I did a UOA. I embraced the thinner stuff for about a decade. Now I've rethought it.


I don't think I've seen it (dino 10w-40) on store shelves for at least ten years.

When you see a "Dollar Store" ..stop in ..find the oil. They've got 10w-40 usually ...for about $0.75/quart.
I've wondered about the popularity of 10W-40 too, and always chalked it up to the ignorance of consumers.

I work for a major lubricants distributor, and it's incredible the amount of 10W-40 we sell. Just guessing (no sales figures in front of me), I'd say it's 2 to 1 versus 5W-30, which has (as you all know) been a common recommendation by many manufacturers for several years. Just two years ago (2002) the ratio was about 3-1.

It's also hilarious how much "Type A" and "Type F" transmission fluid we STILL sell (more correctly, that our customers STILL demand!). When was the last time you saw a transmission that was designed for those? These products mainly sell to convenience stores, and I sometimes imagine Joe Consumer stopping by the 7-11 at 3:30 a.m., "checking" his transmission, deciding it needs fluid and going into the store to get some. He sees on the shelf "Type A", which must be the best available, right? (think "grade A") He buys a couple of quarts at some crazy price and pours it right in. Of course, this is an excellent way to rid our society of "beaters" and polluters...
As I recall, 10w-40 motor oils in the 1970's were the Kings of oil lubrication. They were the most expensive and most heavily advertised. If you bought 10w-30 oil, people would feel sorry for you because you could not afford the 10w-40. I know a mechanic who has his own business that uses nothing but 10w-40 oils even though 95% of the cars that go through there require 5w-20 and 10w-30. He states that he knows what he is doing.
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