Why is 10W40 so bad?

Messages
70
Location
Iowa
Here's a good question. Why is 10W40 so bad? I know people say that since it has a larger spread than a 10W30 (30 points instead of 20) that it can break down a lot faster and cause sludge, ect... But my arguement to that would be this: almost all Honda, Kawasaki, and Suzuki motorcycles recommend 10W40 motor oil for their motorcycle engines. Now remember that an oil for a motorcycle must lubricate BOTH the engine and transmission, operate in higher temperatures, operate in a higher RPM range, and most are air cooled. Also, like my brothers Honda, the motorcycle has no oil filter. On top of all this the manual for the Honda recommends changing the oil every 4 months or 4000 miles. It seems to me that oil for motorcycles would get a pretty good workout. Plus no oil filter and a longer OCI and you get the picture. I just can't believe the bad claims of a 10W40 if it has to be used in these conditions without breaking down. What do you guys think? Oh on a side note I have another good question. My car manual says you can use 5W30 from 32F and anything below (for really cold weather as in -10F, -15F, ect...) It recommends not using the 5W30 above the 32F mark. It also states you can use 10W30 from 0F - 100F+. My question is why can't you use 5W30 when its 80F outside? They are both 30wt. oils when at operating temp. It seems to me the 5W30 would only be icing on the cake - better flow on start up. Is it because the 5W30 can shear down more than a 10W30? Someone please comment on this. Thanks everyone. [Smile]
 
Messages
524
Location
Central Oklahoma
There's a bunch of anti-10W-40s on here, but it seems its OK to have an Amsoil 5W-40, or Mobil 1 SUV/Truck with 40 wt. (BTW, how does the oil know what vehicle its in?!!). The Canadian product MotrLube (a PURE PAO!) is available in 10W-40, 15W-50, and bernardschau from Edmonton reports that he is going to share with us the oil analysis on his car with the 10W-40 soon. He was running long drain interval (15K km's), I think. I find it interesting that the further north you go...often the greater the viscosity. (Euro 5W-40; Motrlube, etc.). Head to Texas, Mexico, and its 5W-20, 0W-30!!! The excuse, er...reason...is no doubt the specific type of engine characteristics. Logic would tell you it should be just the opposite.
 
Messages
250
Location
Phoenix, AZ USA
I THINK the bad rap 10W-40 gets is in dead-dino oil only. Getting that already-thin, much-thinner-when-hot, petroleum-based oil to a 40-hot viscosity requires LOTS of viscosity-index improvers, and we all know there's nothing else good about VIIs. Surely the majority of synthetic 10W-40s require no or at least very little VIIs; I know Red Line 10W-40 contains none.
 
Messages
43,667
Location
'Stralia
The bad rap apparently comes from the old viscoscity index improvers that sheared and sludged....back in the good old days. The 20W-50s with viscoscity indexes of 125 odd. The 15W-40s with viscoscity indexes of 135 odd. Were considered pretty stable. The 10W-40s were close to 150 v.i., and had consequently more of the nasty V.I. improvers. In comparison to today's premium products, M1 5W-50 has 187, and the 0W-40 is 196.
 
Messages
47,789
Location
Everson WA - Pacific NW USA
Nothing at all wrong with a well built synthetic 10W-40. Bad rap is from old (and they were nasty) poorly built petroleum oil based 10W-40's. A very high percentage VI's and pour point agents blended with some crappy group 1 oil....just to call it an SAE 10W-40, fully meeting API. Ahh...the good old API, they'll look out for you.............NOT!
 
Messages
1,462
Location
MD
Do you guys really think todays 10W40 will cause an engine to sludge with sensible OCI's? I don't think so.
 
Messages
5,069
Location
Saratoga, NY
I'm with Shannow & Pablo. 10W40s were introduced decades ago and were consider a miracle-do-everything oil ... but had very early and unstable VII and tended to sludge heavily when pushed hard. I have not been impressed with the conventional 10W40s we have seen here ... even the Chevron sheared down fairly quickly into a 30 weight. [Frown] As Pablo pointed out, a specialty real synthetic is a totally different animal. Do you guys really think today's 10W40 will cause an engine to sludge with sensible OCI's? I don't think so." Probably not ... but the key here is sensible. If you want a 40 weight oil, you're gonna have to change the dino-based lubes fairly often ... maybe follow the standard 3K mile guideline? For most applications, I'd prefer a 15W40 if I want a 40 weight oil in an engine. --- Bror Jace
 
Messages
772
Location
Ohio
Thirty years ago, 10W40 was probably as popular as any other weight. I think GM stopped recommending 10W40 back in the 80’s due to warranty issues. I believe there were a large number of problems on engines under warranty during one very cold winter. And it’s my understanding that the use of 10W40 was believed to be a major contributor to those problems. I don’t know whether the 10W40 issue was related to sludge build-up or low temp pumping, but based on the relative “newness” of the engines involved, I suspect the latter. Twenty-five to thirty years ago, recommended oil change intervals were just beginning to be increased beyond 3K, and typical warranties were 12mo./12k miles. By 1984, an S-10 Blazer came with a 12/12 warranty, and a 3k severe service/7.5k normal service OCI. Recommended oil weights included 5W30, 10W30, and 15W40 depending on expected ambient temperature. 10W40 and 20W50 were not recommended.
 
Messages
2,533
Location
Pittsburgh, PA
quote:
Originally posted by Brian Barnhart: Thirty years ago, 10W40 was probably as popular as any other weight. I think GM stopped recommending 10W40 back in the 80’s due to warranty issues.
[Cool] I was working in an Olds & Cadillac dealer in 1983-84 when we got a letter from GM saying not to use 10w-40 any more. As I recall they said the spread was so wide that it just didn't protect well enough. They said to use 10w-30 for normal use and temps even though the owner's manuals at the time said 10w-30 or 10w-40 were okay. But again, we're talking 20 year-old technology too.
 
Messages
2,480
Yeah I really don't get it either. A dino 5-30 has a spread of 25, a 20-50 has a spread of 30....so what's wrong with a 10-40 with an equal spread of 30? Unfortunately I've stopped using dino altogether so I'll never have the pleasure of personally finding out...although somethin's buggin' me to try a 20-50 dino this summer just for kicks.... [Big Grin]
 

gtm245

Thread starter
Messages
70
Location
Iowa
By the way the motorcycle is a 2003 Honda Rebel with the 250cc 4-stroke engine. It is a street bike but it has no oil filter and recommends 10W40 with 4 month or 4000 miles oil changes. Also this bike is mainly ridden on the highway at 55 - 65 mph. Now for a 250cc bike this is pretty hard on it. The RPM's are getting pretty darn high when your going 65 mph and you have a 200 lb. person on the bike. Anyway I don't think a 10W40 can be as bad as some people say if the oil has to go through this without shearing down and sludging up. Also I am talking about using conventional 10W40; not synthetic. The bike recommends just plain old conventional 10W40 year round. Would there be any negative effects of using a 10W40 in my vehicle over a 10W30 during the summer? The car has 150,000 miles on it and has the Chrysler 3.5L 24V V6. Oh and what else could I use besides AutoRX to clean out some of the varnish and maybe some sludge in it?
 
Messages
903
Location
CA
Even Redline 10w40 will shear if you beat on it hard enough. My last RL 10w40 run went from 14.7 Cst to 12.8 Cst in 5200 miles.
 
Messages
5,069
Location
Saratoga, NY
gtm245, I think in both applications you'll be fine as long as you don't push the interval long enough for crud to build up. In your Rebel (my baby brother had one of these), I'd use a 2,000 mile interval because the shearing will happen quickly. Keep in mind these bike's sumps supply both the engine and the tranny with the same oil. Shearing begins immediately. Sitting for long periods of time shouldn't bother it. Does it have a spin-on filter? Likewise, in your car's engine, the oil will shear down to a 10W30 in a few thousand miles so it won't be "too thick" for very long. Use a good brand (I'd pick Chevron, Havoline or Pennzoil because of the additive package and quality group oil) and change it fairly often. --- Bror Jace
 
Messages
43,667
Location
'Stralia
This is the prime reason why the ratings 10W, 40, 20W, 50 etc are meaningless. It's not a 30 point spread, it's the viscosity index that's important. The 30 point spread 20W-50 is less than the 30 point spread 10W-40 when the viscosity index is looked at.
 
Messages
2,480
So what exactly does the Viscosity Index mean? Should one look for a high number or a low number?? I always thought that higher was better. Or is for eg. M-1 0-40 at 197 a bad thing because it's been known on this board to shear/thin severely/quickly?
 
Messages
509
Location
Las Vegas, NV
<b>Shannow</b>, is correct. For a conventionl group I or II or II+ oil a low viscosity index will mean that the oil is more shear stable since it will need less viscosity index improvers added to the finished product. This is less of a concern for a synthetic motor oil but a synthetic oil with a lower viscosity index will also usually be more shear stable than a similar oil with a higher viscosity index. A good example of this is when you compare Mobil 1 10W-30 to Mobil 1 0W-40. The 10W-30 is very shear stable and the 0W-40 will shear fairly quickly under extreme circumstances.
 

gtm245

Thread starter
Messages
70
Location
Iowa
Do you think a 10W-40 motorcycle oil (such as Honda GN-4) really needs to be used in the Honda Rebel or can I just use a good automotive SL rated 10W-40? The motorcycle oil says it has a special additive package for use in the engine and transmission of the bike, better detergents, blah, blah, blah. Anyway would a good auto oil like Havoline 10W-40 or Castrol GTX work just fine for 2000 miles OCI? [I dont know]
 
Messages
5,570
Location
New Zealand
I am using Fuchs Ultra MC 10/40 in my Japanese Diesels (Pajero,LD20 Nissan)On the Fuchs site they talk about 80,000km oil change intervals with this oil,not an auto oil - but Fuchs aren't too worried about it shearing down if they are prepard to let it go that long.
 
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