Cold Crank Viscosity
- Thread starter Zach_1985
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OVERKILL
$100 Site Donor 2021
It's supposed to be a limit to help guide you in choosing the correct lubricant for the anticipated ambient conditions. So, a 0w-40 for example, has its CCS tested at -35C, so the oil provides an acceptably low impact on cranking speed at that temperature (and of course above).
Yes.
CCS is not about how well the oil pumps, it's about how much resistance the oil gives to turning the engine over. A higher CCS will cause more resistance, meaning more effort needed by the starter motor and more charge taken from the battery.
The MRV test is carried out at 5°C lower than the CCS to test for pumpability. Again, the lower the better.
The MRV test is carried out at 5°C lower than the CCS to test for pumpability. Again, the lower the better.
Good timing. I did a start this morning at -22 F. I have Pennzoil Euro 0w30 in the engine and a 1 year old AC Delco battery. It’s a 6.0 liter LS Chevy engine. The oil pressure sensor is at the top of the engine. There is basically a column of oil in the vertical oil galley between the oil pressure gage and the anti drain back valve in the oil filter sitting adjacent to the oil pan. In a normal 70 degree start it takes 3 seconds to reach 40 psi. This morning it took 10 seconds. This after the engine fired up with no difficulty. YRMV.
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- Nov 13, 2020
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That’s extremely cold to be starting an engine. What time is the day was this?
Why is it extremely cold to start engines at -22? I started it as low as -42c.
Early in the morning. Normally I plug in @ -5F but wasn’t planning on leaving. A change of plans occurred. Western Canada is in a cold snap.
And in terms of pumpability that's a binary value. Either it will or it won't, and that's included in the oil's winter rating.
I've seen -18 degs F this winter thus far. Hopefully, it'll be no colder. Right now, there's a high-wind warning in place till 6 pm tomorrow -- two straight days of 30 to 40 mph, gusting to 75 mph! The temp remains in the lower teens!
Next week, the weather hovers within a few degrees of 0 F -- all week long. Good grief.
For the winter, my GM vehicles are using 0W-40 or 5W-30 synthetic and Fram Ultra or Puro Boss filters, to include quality synth trans and diff fluids. All is good.
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But but but the pump is "positive displacement" and flow is not affected by viscosity.
True, but the main issue regarding pumpability, and a factor that is included in the MRV test, is one of yield stress. No yield stress should be detected in order to have a passing result. If yield stress is detected this means that the oil may not move freely under its own weight - in practical terms this means that in the sump of an engine, the oil pick-up may suck oil into the pump, but leave behind a 'crater' in the surface of the oil which does not back-flow quickly enough to fill itself in, leading to the pump sucking air.But but but the pump is "positive displacement" and flow is not affected by viscosity.
OVERKILL
$100 Site Donor 2021
But but but the pump is "positive displacement" and flow is not affected by viscosity.
The pump isn't affected, and neither is flow IF it isn't on the relief, but the pick-up can be. The delay was likely due to the time required to draw the oil up the pick-up, which @weasley touched-on, as even if the pump did end up on the relief, it wouldn't do so until the engine was enveloped and pressure already registered. That's the purpose of the MRV test (pumpability), however, a couple things to keep in mind:
- Oils are allowed to slip a winter rating in service, as PPD's degrade
- The MRV limit (60,000cP) used to be lower (40,000cP IIRC) when it was based on the AMC/Jeep 4.0L pick-up test, that was deemed obsolete and the new test increased the limit as newer engines were deemed less sensitive. Depending on the pick-up/pump arrangement, certain engine/engine families are going to be more sensitive to this than others.
