quote:
Originally posted by Eiron:
quote:
Originally posted by porterdog:
heyjay, thanks for a seriously informative series of posts; I really learned a lot from them.
Ditto!
I've got a few questions:
1) What is MRV?
2) In used oil, does HT/HS value follow viscosity changes?
3) How does mixing two different oils affect both the winter value ("xW- ") & the HT/HS?
Thanks!
The MRV (Mini Rotary Viscometer) is used soley to determine cold temp pumping capabilities of the test oil in question, it is a "yield" test under low shear conditions. It is defined by the appropriate ASTM 4684 test procedure.
This is in contrast to the CCS (Cold Cranking Simulator) test as defined by the ASTM D5293 test protocol. CCS is a fairly high shear (Ten to the third power or one thousand shears per second)test to mimic the friction encountered as the piston rings are forced to scape along the liner/cylinder wall.
The MRV is a DC electric drive motor with sensitive current monitoring, hooked up to a small test fixture that can be accurately chilled from temps of -18 C (0 F) to -40 C (-40 F). The current required to drive the test fixture is used to derive, with appropriate calculus and other nasty math, a measure of the low temperature FLOW properties.
Empirical testing has determined that a limit of 600 Poise or 60,000 cP (centiPoise)is the "yield" stress at which the vacuum created at the oil pump inlet is no longer capable of drawing oil. The oil tends to cease to slump and just sits there like taffy.
The "absolute" or MRV BPT is run by chilling the test fixture to an absolute 60,000 cP yield, which is not quite as accurate as the careful measurements made to -40 C. I believe the MRV BPT can be run down to -65 F, which is the limit of the chiller.
Depending on the nature of polymeric additives used, and how much used, the HTHS can proportinately track UOA viscosity changes or can even inversely track UOA viscosity changes.
For example, a UOA may uncover slightly higher kinematic testing (ASTM D445) from 12.2 cSt to 13.8 cSt at 100 C. The HTHS (ASTM D4683) may slightly increase from 3.2 mPa s @ 150 C to 3.3 mPa s @ 150 C.
Or, if there are excessive polymeric additives, say in a 5W-30 Dino oil, and excessive blowby, the kinematic testing may uncover a very large increase from 12.2 cSt to 16.8 cSt. Like sludge.
Likewise excessive condensation (Cold weather starting/idling, stop-n-go) tends to cause the polymers to actually separate from the carrier oil. Then you have this sludge of polymer in your sump and a base 5W in yout motor. Coolant contamination will also cause extreme additive separation and nasty sludge.
But that sludge will have poor lubricating properties and the apparent HTHS may have dipped to 2.1 mPa s @ 150 C. It should be apparent that oils can behave much differently in a virgin oil analysis VOA versus a UOA. Only testing can tell you what that change will be. It's a crap shoot.
Mixing is like playing with the Junior Chemistry set: you're in brave uncharted waters. Only VOA and UOA can tell you the results, and you would have to be VERY precise to get repeatable results.
The Chi Square Law tells us that number of samples "n" must be equal to or greater than 324 to have any degree of statistical confidence in such mixing. So I don't "blend" my own oil.
At one time around here, folks used to take 10W and put in up to 10% kerosene to make the oil flow better in extreme cold. That had poor results and often plugged filters.
Actually, the kerosene blend method is now used as a "poor man's" engine flush.
