10W-40 Is it still bad to use?

[Drew]

Is 10w-40 still bad to use? Has the problem with deposits due to viscosity improvers been resolved? I would like to use 10W-40 in my vehicle this summer but if its still not good, I'll stick with the 20W-50.

Thanks

 

[97tbird]

I'd like to know this too, because currently I have 2.5 qts of MC 10/40 mixed in with 2.5 qts of MC 10/30 in my 4.6L.
So far it's been one smooth idle/running experience.

Can I drive around with it or will I be caught and charged by the Anti-10/40 police?

Drew,
Just curious: are 20/50's better than 10/40's? The visc. "spread" is the same, isn't it? or do they have less VI's somehow?

 

[TallPaul]

I had a great UOA with 10w40 Maxlife SL at 3000 miles. Blackstone said I should be good for 4500 miles, and the viscosity held up in the correct range, so no sheer. This was in a Ford 300 cubic inch straight six. I expect 10w40 Durablend would do well also.

Edit: Link to the UOA

[ February 28, 2005, 11:03 PM: Message edited by: TallPaul ]

 

[Geoff]

If you are using 20w-50 vs 10w-40 why not use 15w-40? Should give you better start up and longer OCIs. Most agree the best dino oils out there are 15w-40 HEDOs. Although I am not in the 5w-20 camp, 20w-50 is too thick for most applications in my opinion.

 

[jthorner]

I'm with Geoff. Any application for which 10W-40 or 20W-50 dino oil would be used is IMO a great opportunity to run one of the good 15W-40 fleet oils like Delo or Delvac. I don't see any application where a 10W-40 dino would be better than an 15W-40 fleet oil. If conditions are too cold for a 15W-40, they you are in 5W-30 territory.

John

 

[TallPaul]

quote:

---

Originally posted by jthorner:
If conditions are too cold for a 15W-40, they you are in 5W-30 territory.

John

---

I agree a 15w40 in warmer weather, but if it is too cold for 15w40 (below about 10F per my Haynes manual) a 10w40 will get you down to around zero F. If you get colder than that, then a synthetic 5w40 can be used.

 

[KJA426]

I've read that the 20w-50 is better because even though it has the same thirty point spread, it uses a heavier base oil. Apparently, making a 20 weight act like a 50 weight is better than making a 10 weight act like a 40 weight.

 

[KJA426]

I forgot to add that 10w-40 is still a decent selling grade of oil. Personally, I would want a true synthetic if I was going to use it but it would probably be okay if you stuck to sensible intervals. I would be concerned about shearing in a conventional oil though.

 

[TallPaul]

If we look at viscosity index (VI) as an indicator of how wide the spread is on a multigrade we get the following for Valvoline Durablend SM:

VI / Grade

169 / 5w30
161 / 5w20
155 / 10w40
141 / 10w30 and 15w40
135 / 20w50

So in this case, 5w30 has the worst spread (widest) and 20w50 the best (or least). YOu can see that 10w30 and 15w40 are pretty good too and that 10w40 actually is not nearly as bad as 5w30.

But a wide VI spread is not so bad if it is acheived by higher quality oil. According to the MSDS sheets for Durablend, narrower spreads like 10w30 and 15w40 have more Group I dino than the wider spreads like 10w40 and 5w30. (This is one reason I stocked up on 10w40 Durablend, even though I like the idea of a 15w40. Of course, if I wanted to I could make my 10w40 into 15w40 by mixing in a quart or so of straight 40 weight to beef up the base oil.)

This is not the case with all oils, though, as Maxlife is pretty much the same over all grades (mostly Group I dino and about 15% PAO).

 

[Drew]

I can't use a diesel oil since the engine is oil injected-from the crankcase. Don't want to risk excessive carbon/deposit buildup or potential cat damage.

 

[bmwtechguy]

What? You lost me there. "engine is oil injected from the crankcase"? What kind of engine/ vehicle are you talking about?

 

[Ugly3]

What viscosity does your manual call for?

 

[Alan]

There is nothing wrong with using a 10W40,especially with todays oils.

Don't worry about deposits as long as you use it with sensible intervals.

 

[Patman]

I don't think most 10w40s use as much VII as they once did. If you look at the specs on a lot of the dino 10w40s nowadays, they are very thin 40wts, usually around 12.9 to 13.5. So they don't need all that much more VII to get that type of viscosity. Plus the base oils on newer 10w40s are much better than before, also allowing for less VII.

 

[jsharp]

Looking at the datasheets for Pennzoil, the VI of their 5W-30 is 156, for their 10W-40 it's 153. Close enough to not matter. After seeing how badly their 5W-30 sheared down in a couple thousand miles in my Ford 5.0L, I still wouldn't use a 10W-40 dino oil. Of course I won't use a 5W-30 dino again either unless it's part of an Auto-Rx treatment...

 

[sprintman]

if 10W40 is bad a lot of Australians are in big trouble!

 

[Jimbo]

The dreaded "black death" from 10W-40 of 20 years ago should not be a problem with modern base oils and VII's.

From a viscosity spread standpoint, I have never liked dino 5W-30 either. If it is so cold that a 5W is necessary, maybe a synthetic or blend would be better.

 

[Camu Mahubah]

I really am frightened of 10w-40 and 20w-50 because of a Popular Mechanics magazine I read from the late eighties. Some guy writes in asking a question about which oil to use in his car and the editor/mechanic tells him to steer away from 10w-40 because of VII's.

From what I have learned though I think 10w-40 could be used in someones car you don't like...

 

[sprintman]

That may have been true in the 80's but not today. Mobil Australia tech-line some 6-12mths back said 10W40 now their biggest seller replacing 20W50

 

[ZR2RANDO]

If more folks were actually reading up on oils, the 10w-40 could just maybe make a comeback. From what I have read, it really is a better oil than it used to be, the old problems have been fixed. It may not be a routine 10k oci oil, but for 3k ocis should be just fine. I've got some out in the garage now what with all the discounting/clearances going on.