Is oil pressure influenced by HTHS?

[Fast VW]

I have been searching and I cannot find an answer to this question. I was just trying to figure out if HTHS affected oil pressures. If you compare two oils that have identical viscosities but one oil has a higher HTHS than the other will it cause higher oil pressures?

This is probably a very newb type question but I cannot find an answer. Thanks!

 

[MolaKule]

Oil viscosity and temperature, oil pump wear, cam bearing wear, and filters all have effects on oil pressures.

HTHS is a factor of shearing (microstate) and not on the bulk characteristics (macrostate) of the oil.

 

[TallPaul]

I would think the higher HTHS would increase pressure in certain tight spots, but overall the effect would be negligible.

 

[HondaMan]

Everytime I see MolaKule add a reply, I search his posts to make sure I didn't miss anything else he may have added.

 

[AEHaas]

I would guess that at a sump oil temperature of 302 F there would be no measurable difference in pressure by normal automotive sensing devices. The oil delivered to the oil filter (the usual measuring site) would have a viscosity of 3 cS for a 30 grade oil and 4 cS for a 40 grade oil. The difference is only 1 cS.

Measuring the difference in pressures at 104 F would also be difficult. If there was 1 cS difference in the range of 67 to 68 cS, could any automotive sensor tell between the two viscosities? I say no.

Then again, my belief is that pressure only serves the function of delivering oil to the bearing surfaces. It has no function regarding the separation of parts within the bearing.

aehaas

 

[JAG]

Originally Posted By: AEHaas
I would guess that at a sump oil temperature of 302 F there would be no measurable difference in pressure by normal automotive sensing devices. The oil delivered to the oil filter (the usual measuring site) would have a viscosity of 3 cS for a 30 grade oil and 4 cS for a 40 grade oil. The difference is only 1 cS.

Measuring the difference in pressures at 104 F would also be difficult. If there was 1 cS difference in the range of 67 to 68 cS, could any automotive sensor tell between the two viscosities? I say no.

Then again, my belief is that pressure only serves the function of delivering oil to the bearing surfaces. It has no function regarding the separation of parts within the bearing.

aehaas

You are confusing HTHS viscosity and kinematic viscosity. You should know this, having posted articles online that you wrote on viscosity. I'll probably keep busting your chops until you take down that misinformation that is posted online. It's been years and you've been shown somewhat politely numerous times that you are confused so you had your chances to take it down without great insult.
Also, sump temperature of 302F is not why HTHS is measured at a temperature of 302F. Sump temperatures better not be 302F but oil gets that hot and hotter routinely in certain parts of engines.
Finally, let's suppose that a value of something does change from 4 to 3. In your example, you said the difference is 1 and implied it's not big. It is the percent difference that matters: 25%, which is very significant.

Fast VW, see Slide 9 in this presentation. http://www.astmtmc.cmu.edu/docs/diesel/hdeocp/minutes/2001/hdeocp.2001-05-25/052501ATT12.PDF
It's the best data I found (though doesn't directly answer the question posed) in the time I spent looking. There is some scatter in the data of course. The different oils have different shear stabilities indicated by SSI: Shear Stability Index, where lower number is more shear stable. Two oils with different HTHS but same initial kinematic viscosity (KV) at 100C will likely have different shear stabilities. During use, the one with lower HTHS will very likely be the less shear stable oil (more polymers in it) and if so it will lose more HTHS and KV than the other. So aside from answering the initial question which implied virgin oils, I'm answering it for used oils which is what matters. My answer is that the oil with higher initial HTHS but same KV at 100C is most likely to allow more oil pressure in the used oil condition. There may be exceptions and scatter in the trend but that's life. I think there is data to show better correlation between HTHS and oil pressure (fully warmed engine) than between KV at 100C and oil pressure, but couldn't find a source while I looked.

 

[ekpolk]

Originally Posted By: HondaMan
Everytime I see MolaKule add a reply, I search his posts to make sure I didn't miss anything else he may have added.

Every time (almost) I see Mola post, I stand back, realizing that I probably can't add anything more to the discussion. Thanks Mola!

 

[MolaKule]

JAG,

What I found interesting in the chart for page 9, is that for the higher viscosities, the 15 SSI is shown to have about the same oil pressure as for the 50 SSI.

 

[Fast VW]

Thanks to everyone for the replies. I will check out the link for the information.

Thanks!

 

[SpitfireS]

Unfortunatly the link doesn't work here.
Is that me or the astm website?

Is the statement about the oil pump part of the misinformation?
If I remember correctly I've seen posts on BITOG about crankshaft bearings generating much more oil pressure in the bearing itself by rotating then any normal engine oil pump.

 

[TallPaul]

Originally Posted By: SpitfireS
If I remember correctly I've seen posts on BITOG about crankshaft bearings generating much more oil pressure in the bearing itself by rotating then any normal engine oil pump.
That's the whole thing about energy conserving oils. Typically (and now with the higher quality base oils, this may no longer be true) the energy conserving designation was achieved by using VII that had a property of temporary viscosity collapse, that is, the VII would sort of nest together and reduce in viscosity when going through tight spaces like in the bearings. This, originally a defect in VII became a positive feature in the meeting of fuel economy standards. The temporary collapse was necessary because to make the energy conserving rating an oil had to perform as well as a synthetic in fuel economy. Only way to do it was by cheating, i.e., temporary viscosity collapse. So I saw it as a dirty trick pulled on the consumer and switched to high mileage oil that does not sport the Energy Conserving designation. Of course, all else equal, an energy conserving oil will have a lower HTHS than a non energy conserving oil.