Thin vs Thick Discussion Midterm Examination
- Thread starter AEHaas
- Start date
- Status
Only a cold start on the surface of Mercury or Venus during the day, but you'd need at least a -200W for the early mornings.
LOL, I like that!
Reading these threads would possibly leave some people thinking that if the oil is "too thick" and it is cold the filter is in bypass that the engine is grinding itself to a slow halt, by somehow not getting oil. As you know that's not the case. What I would be more concerned with is how clean that oil is while not being filtered being circulating through my engine. Another reason at least for me why I won't look to squeeze every mile I can get out of an OCI.
There's a problem at start-up that the OP has chosen to ignore over the last (20???) years ?
Cold engines rely on the hydrodynamics of thick oils to keep the parts separated....the primary wear time is the point at which the oil is thnning, and the additives aren't fully functional with heat.
The sequence IVA wear test specifically holds the oil at this sub optimal temperature, where hydrodynamics is poor, and additive function is too, to accelerate the wear by orders of magnitude.
This has been confirmed by at least three oil formulators (some of who worked for the majors), and are familiar with the test regimes, and what they are designed to do.
I know, it and know it well.
Yep. The old saw about 90% of wear happening at "start up" is not really accurate. At least not in the way that most people think. The wear is not just primarily occurring that first couple of seconds after startup when people imagine that no oil is circulating (that happens almost instantaneously, assuming no mechanical defect), it's the "warm up" before oil comes up to sufficient temp where most wear occurs.
LoL talk about start up wear. Just started my 968 after it has been sitting for quite some time. Clack clack clack for about 2 minutes. I guess the lifters were not pumping up. Not worried, might be interesting to see the UOA but I doubt it will show anything, especially being as I have only 1 from this vehicle. I missed driving this car, glad I got it going again. It fired right up which surprised me, the 951 needs about 2 minutes of cranking when it sits for awhile.
People are much more informed now that when this oil series was first posted. Years ago I rebuilt an engine for a friend's 67 GTO and when we first fired it up, one of his friends looked at the oil pressure gauge and saw the oil pressure was 70 or 80 psi and said you have too thick of an oil. I knew he looked a Ferrari chat as he had a Ferrari.
Food for thought:
In our laboratory, it has been observed that in a modern gasoline engine, well designed automotive bearings can be lubricated with oils as thin as [HT/HS] 2.3 mPa.s [or cP] WITHOUT ANY (my emphasis) observable wear on either con-rod or main bearings.
The assumption that lower viscosity lubricants automatically give rise to thinner oil films in key lubricated contacts in a gasoline engine is also open to question, particularly in the case of piston rings. Laser Induced Fluorescence measurements have found that, in a Nissan gasoline engine, the mid-stroke top ring oil film thickness was greater for an SAE-5W/20 lubricant than it was for an SAE-15W/40 lubricant. These effects were also observed in our laboratory for monograde lubricants. Similar effects have been observed by S.L. Moore of BP.
-- R.I. Taylor & R.C. Coy. "Improved Fuel Efficiency by Lubricant Design : A Review." Shell Research & Technology Centre
....And this was from 21 years ago during the earlier days of the use of 20 grade oils. We've had improvements since then.
AEHaas
In our laboratory, it has been observed that in a modern gasoline engine, well designed automotive bearings can be lubricated with oils as thin as [HT/HS] 2.3 mPa.s [or cP] WITHOUT ANY (my emphasis) observable wear on either con-rod or main bearings.
The assumption that lower viscosity lubricants automatically give rise to thinner oil films in key lubricated contacts in a gasoline engine is also open to question, particularly in the case of piston rings. Laser Induced Fluorescence measurements have found that, in a Nissan gasoline engine, the mid-stroke top ring oil film thickness was greater for an SAE-5W/20 lubricant than it was for an SAE-15W/40 lubricant. These effects were also observed in our laboratory for monograde lubricants. Similar effects have been observed by S.L. Moore of BP.
-- R.I. Taylor & R.C. Coy. "Improved Fuel Efficiency by Lubricant Design : A Review." Shell Research & Technology Centre
....And this was from 21 years ago during the earlier days of the use of 20 grade oils. We've had improvements since then.
AEHaas
Regarding question 4 where people say thickening is never the problem:
Evaluation of Oil Performance Using the Tu High Temperature Engine Test With a View to Extending Oil Drain Intervals, Bouvier et al:
Oxidation and thickening is the limiting factor for oil longevity. Generally modern oils thin only 10 percent then thicken up to 60 percent within as little as 96 hrs. of operation ( -in the accelerated test engine. Let me comment that all test criteria are designed to mimic real engine operating conditions but at an accelerated rate).
There is accelerated acidification and corrosive wear that occurs.
Oil thickening was also time dependent. Thickening at 30,000 km was 2 times more when done over 21 months than over a 10 month period. (Change your oil every spring as I suggested before).
AEHaas
Evaluation of Oil Performance Using the Tu High Temperature Engine Test With a View to Extending Oil Drain Intervals, Bouvier et al:
Oxidation and thickening is the limiting factor for oil longevity. Generally modern oils thin only 10 percent then thicken up to 60 percent within as little as 96 hrs. of operation ( -in the accelerated test engine. Let me comment that all test criteria are designed to mimic real engine operating conditions but at an accelerated rate).
There is accelerated acidification and corrosive wear that occurs.
Oil thickening was also time dependent. Thickening at 30,000 km was 2 times more when done over 21 months than over a 10 month period. (Change your oil every spring as I suggested before).
AEHaas
Valve train wear is normal when using 20 grade oils:
Development of the Sequence III G Engine Oil Certification Test, Clark et al:
Engine tests were made more severe again. (Over the years the oil ratings have improved but this has always been despite the increase in testing severity. It was III ...D, E, F, and is now III G). The oil inlet temperature was decreased from 155 to 150 C. The test was 80 and is now 100 hours. There were 8 oil level adjustments allowed now there are 5. The inlet engine air temperature was raised from 27 to 35 C. The engine load was increased 25 percent.
Despite all this the current 0W-20 oils were still GF-4 compliant and showed minimal valve train wear characteristics as long as ZDP levels were higher than 0.03 percent. (The SM rated oils I have seen so far have levels of 0.08)
AEHaas
Development of the Sequence III G Engine Oil Certification Test, Clark et al:
Engine tests were made more severe again. (Over the years the oil ratings have improved but this has always been despite the increase in testing severity. It was III ...D, E, F, and is now III G). The oil inlet temperature was decreased from 155 to 150 C. The test was 80 and is now 100 hours. There were 8 oil level adjustments allowed now there are 5. The inlet engine air temperature was raised from 27 to 35 C. The engine load was increased 25 percent.
Despite all this the current 0W-20 oils were still GF-4 compliant and showed minimal valve train wear characteristics as long as ZDP levels were higher than 0.03 percent. (The SM rated oils I have seen so far have levels of 0.08)
AEHaas
OVERKILL
$100 Site Donor 2021
You may want to visit the UOA section. I'm not sure how old those statements you are quoting are, but we very rarely see oxidative thickening in UOA's, but we see a lot of viscosity loss, particularly in GDI engines where fuel dilution is commonplace.
Journal bearings seem to be less sensitive to lower HTHS than other moving parts in an ICE because of their full hydrodynamic lubrication characteristics. For parts more susceptible to rub together due to low HTHS viscosity with thinner oils, those oils will typically have more AW/AF additives to mitigate wear (ie, giving more "film strength") when the MOFT goes to zero.
The viscosity is used to form the film thickness (MOFT) to keep moving parts separated, and AW/AF additives (film strength) are there to help mitigate wear when the film thickness breaks down and goes to zero, causing moving parts to rub together.
MOFT and HTHS viscosity headroom matters.
Last edited:
Oh boy, so if I put some of that 15w40 Delo 600 ADF in my engine with it's 1100ppm of moly I should be good starting it up when it's -25 out and doing some hard pulls.Moly ... good for redline cold starts.
<--- more sarcasm.Folks please stay out of the discussion if your only input is sarcasm or attempting humor.
Agree or disagree if your going to participate then stay on topic. That means being prepared to have your point challenged and having backup with facts not feelings.
Agree or disagree if your going to participate then stay on topic. That means being prepared to have your point challenged and having backup with facts not feelings.
Adding to post 54, IIRC there was a study previously shown/discussed here some time ago that showed wear rates with different oil viscosities, all formulated the same (having equal AF/AW additives) so that only the viscosity effect on wear was shown. No surprise that more film thickness/MOFT due to viscosity showed less wear in certain engine components.
Last edited:
- Status
Similar threads
