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What oil viscosity / weight for motor or tranny

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Even though Ive been riding for 8 years, I'd like to hear the opinions on this.

I ride an 08 crf450

Im using synthetic motorcycle oil in both my motor and transmission. Now, the manual basically recommends 10w-40 for both based on the typical temps I ride in 50-90 degrees. Now, some of us riders are rebels and chose not to go by the manual either because they'd rather go the cheapest route, believe its not important what weight to use, or believe that their logic supercedes whatever craziness the manufacturer is trying to convince us of.

Since I'm not an automotive/motorcycle engineer or chemist, I personally would be inclined to follow the instructions to the T, however ive been around many people who have "been around the block" with motors and they all have their own theories.

Quick example: my uncles blazer recommended 5w-30 year round, he put 1040 in the spring and fall and 20-50 in the summer. Motor ran til 405k miles all original parts and didnt burn oil. He lead me to believe that thicker oil protected better than watery thin oil, especially on long 80mph trips we would frequently take. The Lucas oil additive basically reinforced this idea with the thick, gummy oil. I did that same thing with my 4.6l mustang until a few strongly warned me against the higher viscosity could blow the motor because it was too thick to reach the bearings and such properly.

So, whats the deal with my CRF450? Can I run Amsoil 20-50 when its 90 degrees? 60 degrees? 40 degrees? 20 degrees? Is thin oil better or thick?

I would think that the thicker oil would be better in the motor/valve due to the constant high revs of my mx riding, and the thicker oil in the tranny would be better due to the clutch abuse that I give it.

Can someone please set me straight???

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Honda user manuals show a recommended viscosity, as well as a chart showing a range of viscosities based on the ambient temperature. Well, at least all the manuals for bikes I've owned do. Does yours?

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Does oil get thicker as you go lower in number ie 0w-30 Than say 10 w-50

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I wouldn't run 20w50 in cold weather, but it's fine for temps over 60F. In the CRF tranny, the most important thing is to avoid "energy conserving" oil. The friction modifiers in them will cause the clutch to slip. All automotive/truck/diesel oils that are 10w40, or heavier, do not contain friction modifiers are safe. All 10w30, and lighter, auto oils are energy conserving and are not safe for your clutch.

You can use just about any oil in the engine side of the CRF.

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Use the manufacture recommended viscosity(s). Thicker is NOT better in a higher revving engine. Nor is thinner.

At high rpm too thick oil is easily aerated into a less than ideal foam/oil mixture, won't drain back the sump as fast , and the bottom ring won't function as intended.

Too thin, and the boundary layer of oil that the parts "surf" on may be thinner than the possible contaminates in the oil. More of a concern on a shared clutch motor (not your crf).

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hmmm. Ok, so basically I shouldnt deviate from the manufacturer's recommended oil viscosity for the motor. WHat about tranny oil. With all the abuse from the clutch, is there ever a point where 20w-50 would be too thick?

btw, im not trying to go cheaper here or anything, just wondering if people have "better" solutions. I hope this didnt come off as a newbie question, but more of a question where I can hear different oil use strategies and the reasoning behind it.

I know all about the non energy conserving which is why I run synthetic motorcycle oil, usually Amsoil or Maxima.

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hmmm. Ok, so basically I shouldnt deviate from the manufacturer's recommended oil viscosity for the motor. WHat about tranny oil. With all the abuse from the clutch, is there ever a point where 20w-50 would be too thick?

btw, im not trying to go cheaper here or anything, just wondering if people have "better" solutions. I hope this didnt come off as a newbie question, but more of a question where I can hear different oil use strategies and the reasoning behind it.

I know all about the non energy conserving which is why I run synthetic motorcycle oil, usually Amsoil or Maxima.

Lot's of people use heavier 15w50 oil in both sides of their CRF's during the summer. It will work fine, especially if you use long service intervals. If you use shorter service intervals, run 10w40 in both sides.

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Oil viscosities are measured at two temperatures, 100C and 40C, the viscosity values are centiStokes. Here is a chart and table of oil viscosity:

Scroll down to the table and you will get a better idea of how thin oil becomes at 100C compared to 40C.

Oil Viscosity Charts

There is one other very important index for oil and it is "High Temp High Shear" (ASTM D-4683) measued at 150C and thought to be more indicative of what actually happens inside an engine. The High Temperature/High Shear Test measures a lubricant's viscosity under severe high temperature and shear conditions. The minimum High Temperature/High Shear viscosity for a 30 weight oil is 2.9 cP. The HTHS values don't change much for SAE grades of 10W-40 and below, nor for those above 20W-40, but there is a 30% increase in minimum HTHS values between a 10W-40 and 15W-40 grade oils. Interesting that all of the 'fleet service' (diesel) oils are 15W-40. So if you want HTHS use at least a 20W-40 grade oil or contact the oil manufacturer for the actual HTHS value. (Some of the Reline oils have very high HTHS values).

What is interesting is this info is not on bottle labels but IMO is very important for engine life under severe conditions.

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very interesting stuff. Which side is more vulnerable to too thick oil? Tranny or motor side? Basically, which side should I be more cautious of putting too high of a viscosity oil?

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Put in what your manufacturer recommends. They have fleets of engineers who worked on the thing, know what they're talking about, have nothing to gain and everything to lose by making bad recommendations. In the minimum they'll give you way better advice about how their products are configured and should be maintained than anything you'll ever find on the internet.

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As far as your comment on auto recomended oil weights...Remember when the auto manufacturers started recomending 5W-30 all year around. That was quite a while ago, over 20 years. The EPA was enforcing CAFE ratings and manufacturers HAD TO improve their fleet mileage. R & D was hugely expensive for relatively small gains. They decided to start recomending a thinner oil like 5W-30 for summer because they would get a "free" boost in their CAFE with little or no R & D. Did it harm engine long term engine life? Do you really think they care if you only get 150K to 175K on a motor instead of 250K to 300K? Nope. They are quite happy with those numbers. A little bit of planned obsolesence along with a free boost in CAFE. Yes, people find they get better long term engine life using a grade heavier than your manual says, ESPECIALLY in summer! Obviously, if you live in the rust belt, you have to consider starting and adequate lubrication in below zero weather.

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5W-30 multiweight isn't "thinner" than single weight oil, that's a misconception. Multiweight viscosity only means that oil will flow as well at low temperatures as a 5 weight single-weight oil, for example, but still maintain viscosity at high temperatures equivalent to a 30 weight single-weight oil. You can achieve exactly the same lubrication using a 5 weight oil when it's freezing and changing to a 30 weight oil in the hottest part of summer. If you do either, change single weight oil according to the climate, or just put in 5W-30 oil and run it year-round, the lubrication of the engine will be exactly the same. You can't screw up by using a multiweight oil, but you sure can by using a 5 weight oil in the summer and 40W in the winter. And THAT's why fleet managers switched to multiweight oils, because the "right" oil was always in the vehicle so they got more mileage out of them. And they did so much better that today it's hard to even find a single-weight oil, and they aren't specified by any manufacturer.

"People find they get better long term engine life using a grade heavier"? Really? How do they do that? By long-term scientific testing? Or is that an old wive's tale? Think about it, "people" don't know as much as the manufacturer, they simply can't. Before there were multiweight oils "people" used to use a heavier grade in older worn engines, but that was back when new engine bearing clearances were three times what they are today. No, these days you usually wear out the rest of the vehicle before you wear out the engine. But if you run a heavier than specified grade oil in a modern motor you'll void the warranty. "People" won't void it, the manufacturer will.

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I'm familiar with the idea that supposedly, at operating temps - 200 - 250 deg., a 5w-30 will have the same viscosity as a straight 30 weight. But it doestn't seem like it lives up to it's numbers. Change oil on a hot auto engine with 5w-30 and compare it to the same situation with a crankcase full of straight 30. The 5w-30 gushes out like water, the straight 30 doesn't. Admitedly, this isn't scientific, just personal observation. The CAFE info I read in an auto publication. Which one I don't remember. It all happened a LONG time ago.

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Good observation and there are two reasons; 5W-30 starts with a 5W base with additives to reduce thinning at operating temperature and the additives break down resulting in a thin 30 oil. The second reason is the SAE grade label on the bottle represents a range of viscosities, Bob the Oil Guy site has a chart showing the ranges of viscosities for each grade. The result is a thick 20 and a thin 30 could have viscosities that are very close. I suspect that the 5W-30 is on the thin end of the range (less additives needed).

Not all oils are created equal which is why there are rating systems for oils, and the common systems such as grade and API ratings are minimums. Most of the engine manufacturers have their own rating systems that are much more stringent, all for longer engine life. The approvals are shown on the bottles of the better quality oils.

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So, can going a step up to 20w-50 be a good thing? yey or neh?

I'd like to know also, I've been running 10w-40 all year-round, but just picked up some 20w-50 for my next change as recommended by a friend with a lot of experience.

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15/40 Rotella T white jug motor and trans(Honda 450) 10/30 for cooler temps.Works for me.👍

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