straight weight syn?

[91FLTCU]

have a ? for the folks here please....
i have a 91 tour glide with the stock EVO, set of wild pigs and carb tuning. not ridden hard except thru the gears once in a while. replaced the oil main feed line with 3/8 ID all the way from the tank to the pump. then went to straight weight HD 50. it has had HD 20w-50 in it but i can tell from the oil pressure when its time to change because of the drop on given days with the same temp. and it gets hot here in central florida!! read about the polymers that are "installed" in the multi weight oils that can "break down" under heat. would like to change to syn because of its superior heat transfer ability but haven't found a "street" straight weight syn. anyone know of one? i can get racing but its not the right package of additives. thanks in advance, bill

 

[hk33ka1]

Well if you want to try a syn how about Amsoil's 20W50. I know more than a few people in Florida using this and other 20W50 syns in their Evo's and TC88-95's in the summer with great results. If you really want a straight weight Amsoil makes their racing SAE 60. You could call or E-Mail Amsoils tech guys about the additive package and it's suitability in a street ridin HD. I have been using the Amsoil 20W50 in the motor, Amsoil 10W40 in the Primary and the Amsoil 75W90 in the tranny of my 2002 Softail for a couple of years now and I do not need to top up between changes ie. no burn off.

 

[Chris]

I'd try M-1 15-50.

 

[91FLTCU]

thanks ya'll, i'm definately going to Amsoil after i do the gasket set. just wanted to know if there was a street version of a straight weight on the market...for the time being. thanks, bill

 

[DNS]

If by "straight weight", you mean a synthetic with no viscosity index improvers, Amsoil 20W50 and Mobil 1 15W50 come very close as they use little or none. There are a few synthetic oils that don't contain viscosity index improvers. From that standpoint, they could be called straight weights. However, since they usually display the same resistance to thinning at higher temperatures as a comparable multiweight dino oil (one with viscosity improvers), they are usually labeled as multiviscosity oils. It's primarily the viscosity improvers than shear down rather than the base oil.

 

[Michael SR]

quote:

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Originally posted by DNS:
There are a few synthetic oils that don't contain viscosity index improvers. From that standpoint, they could be called straight weights. However, since they usually display the same resistance to thinning at higher temperatures as a comparable multiweight dino oil (one with viscosity improvers), they are usually labeled as multiviscosity oils.

---

part of what you said there confused me. from reading spec sheets, it appears that straight weight oils have a higher ht/hs relative to their weight, as compared to multigrade oils of the same (hot) weight. the implication is that straight weight oils resist thinning better when going from 100° C to hotter.

yet you seem to be saying that a multiweight oil resists thinning better than a straight weight. i'm guessing you mean in the temp interval between very cold and 100° C? because that part is true.

but this suddenly made me wonder, then why does it not resist further thinning beyond that? do the VIIs simply break down past a certain temperature?

-michael

 

[Jim]

My understanding of VI improvers is that the molecules unwind at high temperatures creating the effect of higher viscosity. They can however be forced to collapse under high shear and pressure.
If they have totally unwound at 100 degrees C then further heating would make the multi weight oil start to loose out to the non VI improved oils.
I also think that Schaeffers makes a single weight synthetic oil but you have to buy a minimum of 5 gallons.

 

[DNS]

quote:

---

Originally posted by Michael SR:

quote:

---

Originally posted by DNS:
There are a few synthetic oils that don't contain viscosity index improvers. From that standpoint, they could be called straight weights. However, since they usually display the same resistance to thinning at higher temperatures as a comparable multiweight dino oil (one with viscosity improvers), they are usually labeled as multiviscosity oils.

---

part of what you said there confused me. from reading spec sheets, it appears that straight weight oils have a higher ht/hs relative to their weight, as compared to multigrade oils of the same (hot) weight. the implication is that straight weight oils resist thinning better when going from 100° C to hotter.

yet you seem to be saying that a multiweight oil resists thinning better than a straight weight. i'm guessing you mean in the temp interval between very cold and 100° C? because that part is true.

but this suddenly made me wonder, then why does it not resist further thinning beyond that? do the VIIs simply break down past a certain temperature?

-michael

---

I'm referring to multi-weight vs a straight weight of the same viscosity as the mult-weight's base oil. A conventional 10W40 for instance, is a straight 10 weight with viscosity improvers added. I doubt that a straight 10 weight will be any better at high temperatures than a 10W40. Even allowing for shearing of the viscosity improvers, the 10W40 isn't likely to thin down past a 10 weight. Now if you're comparing a conventional 10W40 to a conventional 30 weight oil, it's a different story. Over time, as the viscosity improvers shear down, the 10W40 becomes a 10W30 and then a 10W20. If the 10W40 has turned into a 10W20, it's not going to do as well at high temperatures as the straight 30.

The other part of what I was getting at is that most synthetic oils have viscosities at 0 and 100 degrees that qualify them as multiweight oils and they are usually labeled that way. Yet because they don't have any viscosity improvers, they could also be considered a straight weight. Many of them do however contain a small amount of viscosity improvers to extend their multi-weight characteristics. Amsoil's heavy duty 20W50 used to (and probably still does) meet the 0 and 100 degree viscosities required of 1 20W50 without any viscosity improvers. So it could be called a straight weight or a multi-weight. Many other synthetics such as Mobil 1 15W50 use very little viscosity improver. Without any viscosity improvers, it would still probably qualify as a 15W40.

[ June 06, 2004, 05:05 PM: Message edited by: DNS ]

 

[91FLTCU]

DNS, thanks for the very helpful information. thats exactly the info i was looking for. selection of oil just became a non-confusing issue. looks like Amsoil gets the nod for having little or no, viscosity improvers. thanks again to all the responded! bill