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Discussion Starter · #1 ·
Hello, I’m new here and just purchased a 2004 bonneville t100 and was wondering what oil weight to use? The previous owner was using a combo of 2quarts 20w50, 1quart 10w30 and the last being 5w20.
The brand? Castrol gtx for all.
The PO was a mechanical engineer and had plenty of convincing reasons as to why I should use this mixture- I’m thinking I’m gonna stick with it unless convinced otherwise. Thanks
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I am a mechanical and aerospace engineer and I would like to hear the logic behind the mixture. Not knocking it - just curious. I am and have been a long-time proponent of Castrol GTX oils. Just seems a little odd to mix one qt. of semi-synth. with three of standard petroleum with all the different weights to end up with around a 10/30W ?

Nice looking bike & looks like a great find!
 

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"The PO was a mechanical engineer and had plenty of convincing reasons as to why I should use this mixture- I’m thinking I’m gonna stick with it unless convinced otherwise. Thanks"

Obsessive compulsive disorder? Typical engineer? Maybe both?
 

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Discussion Starter · #5 ·
Be interesting to share the logic of the mixture.
Castrol Power One was supplied with my 2012 Bonneville (Simi Valley California dealer) and my 2022 Bonneville (Las Vegas Nevada dealer)


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I think the idea was that the 50 would help in hotter conditions while the lower viscosity added helped dilute the mixture to provide better circulation upon cold starts/ all around
 

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Discussion Starter · #6 ·
I am a mechanical and aerospace engineer and I would like to hear the logic behind the mixture. Not knocking it - just curious. I am and have been a long-time proponent of Castrol GTX oils. Just seems a little odd to mix one qt. of semi-synth. with three of standard petroleum with all the different weights to end up with around a 10/30W ?

Nice looking bike & looks like a great find!
I think the idea was that the 50 weight would provide better protection on hotter days while the lower viscosity added helped with circulation and acted like a thinner to the 50 weight. Would you keep it? Change to one single weight? It seemed to work well for the PO
 

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That's exactly what I get using Mobil 1 V Twin 20w 50. Without all the extra work. Besides its all synthetic.
 

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I think the idea was that the 50 weight would provide better protection on hotter days while the lower viscosity added helped with circulation and acted like a thinner to the 50 weight. Would you keep it? Change to one single weight? It seemed to work well for the PO
Not knowing your temp range you will be using the bike - If it was mine, I would go with something down the lines of a 10W/30 or 20/50W or as I use in my Bonneville a 15W/40 Delo. I would not mix all the oils to make a mixture. By adding the lower viscous oils to the higher viscous oils you are just basically just thinning the 50W down. I really do not see the benefit. I do not believe it hurts anything at all if you wanted to stick to it, I just don't see why you need to go to all the trouble. Choice of synth or not is a whole other subject that always goes south when brought up, just as using diesel designation oils with the additional Zink protection debate begins.... :oops:
 

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2 part full syn, 1 part dino oil, 1 part bacon fat. Trust me.
Bacon fat. So that's why everyone wants to ride behind you.

eire49, depends a little on the temps in your riding environment. We've got pretty hot summers and I don't ride in the snow, so I use Amsoil 15W/50 full synthetic. I think mixing weights is generally discouraged. Just pick a high quality JASO M compliant motor oil with a weight range suitable to your weather. It's really not that critical, especially if you change your oil every year (and you should).
 

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Hi Eire49
I cannot see on any of the 4 bottles that the oil is suitable for wet clutch motorcycles.
As @PapaSmurfMC pointed out the wet clutch suitability standard is Jaso M, if the oil is suitable for motorcycles, this standard will be printed in the oil spec on the back of the bottle.
The Friction modifiers in non Jaso M oils contaminate the clutch plates and can cause clutch slip, these non Jaso M oils are meant for cars not motorcycles.

regards
Peg.
 

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I cannot see on any of the 4 bottles that the oil is suitable for wet clutch motorcycles.
None of them are. I checked.
As @PapaSmurfMC pointed out the wet clutch suitability standard is Jaso M, if the oil is suitable for motorcycles, this standard will be printed in the oil spec on the back of the bottle.
All of the Castrol products that meet the Jaso M specs also say "Motorcycle" on the front (and all the one's I've see recently have a drawing of a motorcycle on the front).
The Friction modifiers in non Jaso M oils contaminate the clutch plates and can cause clutch slip, these non Jaso Moils are meant for cars not motorcycles.
Indeed. Using non Jaso M oil with a wet clutch is asking for trouble.
 

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Be interesting to share the logic of the mixture.
Castrol Power One was supplied with my 2012 Bonneville (Simi Valley California dealer) and my 2022 Bonneville (Las Vegas Nevada dealer)
I'm sure there's an engineer somewhere that might explain it, but it's propably take 50k words.
 

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As Back 2-2 already pointed out, the concoction will reduce the high temperature capability.

I am not overly concerned with what brand of oil anyone prefers, although I strongly prefer to not change brands from what is first used.

I used the basic Castrol motorcycle oil for my first seven motorcycle. Never an issue.

I used Harley 360 in my two Sportsters, which is what they were prepped with.

However, I did not continue with Honda 10w40 nor BRP 10w40, because neither were rated over 104 F and did not have 10W50 suitable for my area. So Castrol Power One was my choice.

After the SoCal Triumph dealer introduced me to the Castrol 10W50 pure synthetic Power One, I have not looked back.

There are certainly other good oils, such as Rotilla and Mobil 1. Motul is excellent quality. 10W60 allowed my Moto Guzzi to operate in temperatures up to 116 F. with a capacity of only 2 liters.

Pick a major brand, change it within the recommendation, preferably much earlier, use pure synthetic and make sure to use the proper weight for the ambient range. That combination is cheap insurance.
 

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My suggestion to continue with the same oil brand is concerned that there could be a conflict between additives.

In 1977 I sold a 1971 Chevelle Malibu to my best friend. I bought it new and it was serviced with only 10W-30 Quaker State for over 70,000 miles.

My friend preferred Castrol and switched. Previously the engine had no measurable oil consumption but did do after the change.

After a few years he sold it to a mutual friend who went back to using Quaker State and the oil consumption stopped.

I do not view this as a negative for Castrol automotive oils but rather a case in point for not changing an oil brand.
 

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I'm a mechanical engineer too and one thing I know, get a bunch of them together and they will disagree and argue on a lot of oil related issues and everything else and with many hubris gets in their heads and it takes a tradesman like a millwright (fitter and machinist in Australia) to knock some practical sense in their heads.

for me I use an oil that is moto specific, and my bike has clocked up 180,000 kilometers and still goes well. brand not important as long as it's a reputable brand, which for me has been Silkolene Comp 4 only beause I can get it cheap on special, but lately Motorex being cheaper still..
the owners manual nominates 10w-40 or 15w-50. I use the latter as summers here can be warm.
with 20w-50, I have tried that but found when the engine was cold it was hard to shift gears until the engine fully warmed up. this is because it's thicker at lower temps compared to the former 15w-50, but the same viscosity at normal operating temps.
 

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this is what I use and have done for many years 143,000km on my Deauville had this bike for 13 years, and 220,00km on one of my bmws k100 that I had and never had a problem
 
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