HTHS and flowability?

[slybunda]

hello, was trying to understand HTHS rating with 2 oils rated at 5w-30

one is specced at
53 mm2/s @ 40c
9.8 mm2/s @ 100c
and hths of 3.1

other has rating of
57 mm2/s @ 40c
10 mm2/s @ 100c
and hths of 3.41

would there be a large difference in oil thickness between these 2? the viscosity numbers are very close but hths is bigger difference?

 

[slybunda]

just to add those mm2/s ratings are same as cSt rating.

 

[bobbydavro]

Viscosity is measured under gravity.

HTHS measured at high shear.

The difference here is the polymer used and its 'temporary shear stability'

Pumpability (is this ' flowability') is another parameter measured by CCS or MRV, which is under very different conditions again

 

[slybunda]

hmm so out of those 2 specs i listed, will there be any difference in thickness or flow?

 

[A_Harman]

The oil with the higher HTHS will form a thicker oil film on moving surfaces, and will have slightly lower flow through the oil system.

 

[slybunda]

hmm so how much % difference in thickness will there be between hths 3.1 and 3.4?

 

[147_Grain]

Originally Posted By: slybunda
hmm so how much % difference in thickness will there be between hths 3.1 and 3.4?

About 10%, which can mean a lot as far as engine performance or protection (IF necessary) is concerned.

 

[slybunda]

thats odd, those 100c ratings are a lot closer at 9.8 and 10 , so i thought there would not be that much difference.

 

[A_Harman]

It's the HTHS viscosity that is the bettter indicator of how thick the oil film will be in a bearing. Some oils are better than others at maintaining their viscosity when sheared between moving surfaces.

 

[slybunda]

So does that mean the oil with the higher hths will be thicker from cold?

 

[Quattro Pete]

Originally Posted By: slybunda
So does that mean the oil with the higher hths will be thicker from cold?

No, it does not mean that. HTHS only tells you the viscosity at 150 deg. C.

As was already posted by another user, CCS or MRV tests are used to determine flow at very cold starting temps.

 

[Shannow]

Originally Posted By: slybunda
So does that mean the oil with the higher hths will be thicker from cold?


With multigrade oils, they have two different "viscosities" depending on how fast the moving surfaces are moving, due to the polymers that give the Viscosity Index shearing (temporarily or permanently).

The KV is representative of what happens in the sump, oil lines, coolers, flowing back from the cylinder head etc.

The HTHS is representative of what happens in the bearings, the ramps of a cam, pistons and rings. It is the viscosity that you would design your bearing parameters.

HTHS of a 10cst SAE30 will be the same at both low and high shear rates, and be about 3.6...it will still flow back from the heads, through the lines, and from the sump into the pickup the same as either of your listed examples (at 100C).

As QP says...cold is a different measuring system for a different reason.

 

[slybunda]

Ahh that makes sense now. So the 2 oil specs I listed will be similar at 100c but at 150c in the bearings the one with the higher hths will be thicker.

 

[Shannow]

Close, but not quite.

In the areas that are under high shear rates, both will be thinner than their KV would indicated.

Most likely, at 100C, oil 1 would be 7.1cst (est) in the bearings and 9.8 in the galleries. oil 2 would be 7.5cst (est) in the bearings and 10cst in the galleries.

A non-VIIed oil will have the same viscosity in either. e.g. Pennzoil HD30 will be 11.5cst in the galleries AND in the bearings at 100C, as it doesn't have polymers. At 150C, it's probably also around 3.6+cst versus the other two...It will also be thicker at every temperature colder than 100C than either of your examples.

 

[slybunda]

ahh ok, the 2 oils in my example were mobile 3000 (hths 3.1) and motul 8100xcess (hths 3.4)

i will give the motul a try next time, seems like it may be bit better without being thicker when cold compared to the mobil oil.

 

[slybunda]

Does hths affect oil consumption?

 

[Jetronic]

not sure, but hths and KV are related anyway. chances are the oil on the cilinder walls and on the pistons will be closer to 150°C than to 100°C anyway. Same story around the valve stems or in the turbo bearings.

So in hindsight, yes.

 

[Doug Hillary]

Hi,
To the OP, as usual Shannow and A_Harman have provided great answers IMO

Endeavouring to establish the wear performance of a lubricant in a particular engine family let alone a number of engine families will typically only be a hypothesis here on BITOG. How the lubricant performs in terms of its durability – maintaining viscosity, TBN/TAN relationship - and the likes via UOAs is a great task and for some a lesson in lubricant economics

There are many variables in engine design such as metallurgy, ring pack positioning, valve train actuation, various internal operating clearances, filtration etc. and how the lubricant is utilised within the engine. In some it is used as a hydraulic medium, a prime coolant or an emission control medium and the likes

This is why OEM Lab Tests are typically followed by in-use performance monitoring (field testing) to confirm the Lab results and to establish the possible need for formulation changes.

API & ACEA Standards are set for Oil Companies to use as a base line in general terms and going any further than this requires specific OEM Certification. IMO this is as it should be and in my world as it has been for the last six decades!

As an example most real wear most likely occurs via abrasive particles below around 3microns so the oil film must meet the overall needs of the particular engine family. HTHS viscosity is therefore a critical part of the oil’s formulation and typically a minimum will be established by the OEM.

As another example; some pyrometer temperatures in heavy high speed diesel engine use would shock many here on BITOG
In my vehicles we established a “long climb” average of 450C. Normal use average was around 375C. The maximum allowable is higher than these figures. So the lubricant must have sufficient film durability at around these temperatures to avoid any likelihood of metal to metal contact and to resist excessive oxidation. The flow rate through the turbocharger must be sufficient too and the film must be clean as well bearing in mind the likely film thickness here and its strength! Again the minimum permitted HTHS viscosity is obviously important

So it is likely that using a lubricant with an HTHS viscosity lower that the OEM’s requirement will cause increased wear and most likely an increase oil consumption.

As to flow, I suggest you search Shannows’ many Posts on this subject to increase your knowledge

I my own case I have always used the lightest viscosity certified lubricant as mandated by the OEM

I hope this ramble helps a little

 

[slo town]

Doug, a very informative, well organized and sequenced, easy to read post. Thank you.

At the risk of sounding "silly", you seem like a very nice man. I'm sure your family loves you and that you have many friends.

Scott

 

[userfriendly]

Can the flash point be used as an indicator of a lubricant's
fitness for high temperature operation?

If we are seeing elevated temperatures as high as 450C
(that is not a typo is it?) how can we pick one engine
oil that is better than the next.

HTHS measured at a cool 150C.