Can the HTFS viscosity be an indicator of oil burning?

[ExpandW]

In the car communities I frequent, many people are on the hunt for the elusive 'unicorn oil'—an oil that doesn't get consumed over the oil change interval (OCI). I've noticed that different brands of oil, even when they share the same viscosity grade, show varying levels of consumption over the OCI for different users. This observation led me to wonder why that might be.

My hypothesis is that the difference comes down to the High-Temperature, Full-Shear (HTFS) viscosity. If a given oil is getting burned because its passing the piston rings, then a thicker oil in that area should theoretically burn less, even if it shares the same viscosity grade with another oil. Since HTFS viscosity is particularly relevant in areas like the piston rings, could choosing an oil with a higher HTFS viscosity reduce oil consumption compared to one with a lower HTFS viscosity? For this discussion, I'm only considering worn or caked piston rings as culprits for consumption.

Take Ravenol, for example. Their 30-grade oils have HTFS viscosity values ranging from 1.94 to 2.92 — the former being a VW-specific oil and the latter a racing-spec oil, both fully synthetic. Is this range significant enough to notice a difference?

 

[edyvw]

In the car communities I frequent, many people are on the hunt for the elusive 'unicorn oil'—an oil that doesn't get consumed over the oil change interval (OCI). I've noticed that different brands of oil, even when they share the same viscosity grade, show varying levels of consumption over the OCI for different users. This observation led me to wonder why that might be.

My hypothesis is that the difference comes down to the High-Temperature, Full-Shear (HTFS) viscosity. If a given oil is getting burned because its passing the piston rings, then a thicker oil in that area should theoretically burn less, even if it shares the same viscosity grade with another oil. Since HTFS viscosity is particularly relevant in areas like the piston rings, could choosing an oil with a higher HTFS viscosity reduce oil consumption compared to one with a lower HTFS viscosity? For this discussion, I'm only considering worn or caked piston rings as culprits for consumption.

Take Ravenol, for example. Their 30-grade oils have HTFS viscosity values ranging from 1.94 to 2.92 — the former being a VW-specific oil and the latter a racing-spec oil, both fully synthetic. Is this range significant enough to notice a difference?

I had a higher consumption of some racing oils than street oils of the same grade.

 

[buster]

In the car communities I frequent, many people are on the hunt for the elusive 'unicorn oil'—an oil that doesn't get consumed over the oil change interval (OCI). I've noticed that different brands of oil, even when they share the same viscosity grade, show varying levels of consumption over the OCI for different users. This observation led me to wonder why that might be.

My hypothesis is that the difference comes down to the High-Temperature, Full-Shear (HTFS) viscosity. If a given oil is getting burned because its passing the piston rings, then a thicker oil in that area should theoretically burn less, even if it shares the same viscosity grade with another oil. Since HTFS viscosity is particularly relevant in areas like the piston rings, could choosing an oil with a higher HTFS viscosity reduce oil consumption compared to one with a lower HTFS viscosity? For this discussion, I'm only considering worn or caked piston rings as culprits for consumption.

Take Ravenol, for example. Their 30-grade oils have HTFS viscosity values ranging from 1.94 to 2.92 — the former being a VW-specific oil and the latter a racing-spec oil, both fully synthetic. Is this range significant enough to notice a difference?

Some oils for reasons I don't understand form a better piston ring seal. Noack doesn't correlate well with oil consumption. I think viscosity is a factor, but so is the chemistry.

 

[ARCOgraphite]

I would guess a little oil getting by stem seals and also into the second ring set is not a bad thing. On my Ford that can drink like a Frat boy when presented the "right sauce" seemed to poo-poo a purportedly low VM 10W30 QS.
Never had to add with that stuff.
Before D.I. I would top oil an engine if it was not a drinker

 

[OVERKILL]

In the car communities I frequent, many people are on the hunt for the elusive 'unicorn oil'—an oil that doesn't get consumed over the oil change interval (OCI). I've noticed that different brands of oil, even when they share the same viscosity grade, show varying levels of consumption over the OCI for different users. This observation led me to wonder why that might be.

My hypothesis is that the difference comes down to the High-Temperature, Full-Shear (HTFS) viscosity. If a given oil is getting burned because its passing the piston rings, then a thicker oil in that area should theoretically burn less, even if it shares the same viscosity grade with another oil. Since HTFS viscosity is particularly relevant in areas like the piston rings, could choosing an oil with a higher HTFS viscosity reduce oil consumption compared to one with a lower HTFS viscosity? For this discussion, I'm only considering worn or caked piston rings as culprits for consumption.

Take Ravenol, for example. Their 30-grade oils have HTFS viscosity values ranging from 1.94 to 2.92 — the former being a VW-specific oil and the latter a racing-spec oil, both fully synthetic. Is this range significant enough to notice a difference?

How are you arriving at the HTFS viscosities? Are you using Gokhan's estimations?

 

[ExpandW]

How are you arriving at the HTFS viscosities? Are you using Gokhan's estimations?

Yes.

Here's a table I made for Ravenol oils

I did mark in red oils that produced weird results from the formulas, not sure why.

 

[ARCOgraphite]

I reviewed Gokhan's table (valid or not) and chose an (available to me) oil with a high HTFS; and it worked in eliminating consumption in my application.
S1 or 1
whoop de do for the stats guys.

That oil has been reformulated since then. Not an ACEA or Euro approval fluid - not that it matters much in a typical passenger car driven conservatively.

 

[OVERKILL]

Yes.

Here's a table I made for Ravenol oils

I did mark in red oils that produced weird results from the formulas, not sure why.

OK, I think it's very important to keep in mind that these are just estimates and the results should be taken with a grain of salt. While the calculations MAY be illustrative of the amount of VII polymer and the base oil viscosity of the blend, it's based on working backwards the data from example blends and averaging them to arrive at results that seemed reasonably consistent. It cannot accurately predict the behaviours of the various base oil and VII combos, which is why we get odd results from certain products.

It's a fascinating exercise, don't get me wrong, and I appreciate the effort Gokhan put into developing and refining it, but I wouldn't use it to influence my oil selection.

Example: Valvoline Daily Protection SAE 30 has a -2.18% VII content according to the calculator, the SAE 50 is -1.92%.

But it gets better!

The Bio-based oils really go off the reservation.

The VII content of the EVOLVE EvoSyn oils ranges from 5.13% (5W-40) to -8.31% (5W-30)

The HPL No-VII oils range from 4.52% (10W-20) to -5.77% (Euro 5W-20), even though we know none of them have VII's at all.

 

[Jetronic]

OK, I think it's very important to keep in mind that these are just estimates and the results should be taken with a grain of salt. While the calculations MAY be illustrative of the amount of VII polymer and the base oil viscosity of the blend, it's based on working backwards the data from example blends and averaging them to arrive at results that seemed reasonably consistent. It cannot accurately predict the behaviours of the various base oil and VII combos, which is why we get odd results from certain products.

It's a fascinating exercise, don't get me wrong, and I appreciate the effort Gokhan put into developing and refining it, but I wouldn't use it to influence my oil selection.

Example: Valvoline Daily Protection SAE 30 has a -2.18% VII content according to the calculator, the SAE 50 is -1.92%.

But it gets better!

The Bio-based oils really go off the reservation.

The VII content of the EVOLVE EvoSyn oils ranges from 5.13% (5W-40) to -8.31% (5W-30)

The HPL No-VII oils range from 4.52% (10W-20) to -5.77% (Euro 5W-20), even though we know none of them have VII's at all.

That shows the numbers posted in product data sheets are likely off, possibly rounding errors compounding.

 

[OVERKILL]

That shows the numbers posted in product data sheets are likely off, possibly rounding errors compounding.

The problem is that different base oils, VII's and their combinations behave differently, and this can't be modelled via a single, universal, equation. I'm aware as to why the figures are all over the map for the HPL monograde products, but I'm not at liberty to share the details of that discussion without running it by Dave first. I can state however, that it's not due to PDS inaccuracy but rather base oil behaviour. VII doesn't factor in here, because the product doesn't have any.

 

[twX]

My hypothesis is that the difference comes down to the High-Temperature, Full-Shear (HTFS) viscosity. If a given oil is getting burned because its passing the piston rings, then a thicker oil in that area should theoretically burn less, even if it shares the same viscosity grade with another oil. Since HTFS viscosity is particularly relevant in areas like the piston rings, could choosing an oil with a higher HTFS viscosity reduce oil consumption compared to one with a lower HTFS viscosity? For this discussion, I'm only considering worn or caked piston rings as culprits for consumption.

The shear rate of oil between the rings and the liner changes throughout the stoke, and typically ranges from under 10^6 1/s near BDC, to over 10^7 near TDC between the late compression stoke and early combustion stroke.

You might expect HTFS to be relevant to oil consumption in the part of the engine cycle when shear rates are high, but these high shear rates only occur when combustion chamber pressures are high. Blowby will pushing oil toward the crankcase at this time, so there won't be much oil getting past the rings. Reverse blowby that forces oil into the combustion chamber will mostly occur closer to BDC where shear rates are lower.

Also, the shear rates I mentioned only apply to the oil film between the piston and liner. A lot of the oil consumption at the pistons will be from oil getting through the ring grooves or the top ring gap, where shear rates are probably low enough that the oil doesn't shear-thin at all. It may even be an oil/gas mist. HTFS could have some relevance to oil consumption, but I don't think it would be nearly as relevant as HTHS, or even KV100.

If two oils have the same HTHS and use the same type of base oil, the higher-HTFS oil will have thicker base oil and will be less volatile. This might reduce oil consumption, but not directly due to the viscosity.

 

[chris719]

The numbers are off for some of the oils, but you can see that "HTFS" definitely correlates with KV100 to HTHS ratio. A quick and dirty HTFS is just picking the oil with the highest HTHS per KV100.

 

[SubieRubyRoo]

In the car communities I frequent, many people are on the hunt for the elusive 'unicorn oil'—an oil that doesn't get consumed over the oil change interval (OCI). I've noticed that different brands of oil, even when they share the same viscosity grade, show varying levels of consumption over the OCI for different users. This observation led me to wonder why that might be.

My hypothesis is that the difference comes down to the High-Temperature, Full-Shear (HTFS) viscosity. If a given oil is getting burned because its passing the piston rings, then a thicker oil in that area should theoretically burn less, even if it shares the same viscosity grade with another oil. Since HTFS viscosity is particularly relevant in areas like the piston rings, could choosing an oil with a higher HTFS viscosity reduce oil consumption compared to one with a lower HTFS viscosity? For this discussion, I'm only considering worn or caked piston rings as culprits for consumption.

Take Ravenol, for example. Their 30-grade oils have HTFS viscosity values ranging from 1.94 to 2.92 — the former being a VW-specific oil and the latter a racing-spec oil, both fully synthetic. Is this range significant enough to notice a difference?

HT/FS is a theoretical calculation by one (ex-) board member who made this idea up. It has been discussed with several actual oil blenders, who have not placed much faith in that idea.

Stick with HT/HS. The other thing it appears you’re missing from your idea is the fact that oils with higher levels of poor quality VIIs will shear those down and give you the makings of stuff that will begin to accumulate in the oil rings, drain back holes, and end gaps and be “sticky”. Once they begin to accumulate they will attract more, and you end up with something like the Toyota oil burning issues.

Pick an oil with the correct HT/HS for your engine, that also has either low levels or high-quality VIIs, and then track oxidation & insolubles as you find your optimal OCI. If you’ve got an existing oil burner, use some HPL EC30 mixed in with an oil that has an HT/HS at least 0.5 higher than what you used in the past until it’s cleaned up.

 

[Plumb Bob]

I had a higher consumption of some racing oils than street oils of the same grade.

I've had the same experience.