Oil specs

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Tx, USA
I'm not new to this by any means, but I'm trying to figure out which numbers best represent cold starting thickness. For example, the 40 degree C for Castrol 0w40 is 79, which is lower than most 40 weights, but higher than most 30 weights...but the Ccs at -35 C is still 5900 iirc, which is in the 5w range...what I'm asking is...is the 40 C more relevant to starting temp or operating temp? Since 40 Celsius is only 104 F
 
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40C is operating temp, but not fully warmed. The CCS of your 0w40 at -35 simply shows that the oil achieved what was required for a 0wxx oil. 5wxx has to achieve its numbers at -30 so it's not a direct comparison. But -- a 0wxx oil will be thinner at really low temperatures than a 5wxx. No difference between the two at (someone will get the exact # I'm sure) above freezing. You're in SC though, so unless you are taking a winter road trip to the frozen north you won't have to worry about it!
 
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Stang40

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Thanks Kuato, that's what I was thinking, but it almost made it look like a 0w40 was thicker at start up than a 5w30, which doesn't make since.
 
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Castrol is notorious for telling you the spec for the weight range, not their oil. They're not really helping the consumer looking for actual data. Look at PQIA for the 5w-30 Edge and the max for a 5w @-30c is 6,600cP...the oil tested at 5,544. PQIA Whereas their PDS shows max 6,600cP Castrol PDS
 
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Originally Posted By: Stang40
Thanks Kuato, that's what I was thinking, but it almost made it look like a 0w40 was thicker at start up than a 5w30, which doesn't make since.
Well, there IS a temperature at which the 40 weight becomes thicker than the 30 weight oil, and it will remain so as the temperature climbs. Someone referenced a site a few months back (couldn't find it) where you could plug in oil weights and get an estimate of viscosity, based on 3 data points (low temp viscosity, 40C and 100C). I compared a 5w20 to a 0w30, and the 0w30 was thinner until about the freezing mark, after which it became thicker and stayed that way all the way up the chart. I'd imagine your comparison would be similar, but the oil temperature where one oil becomes thicker might be somewhat different. The thing is that the right oil will act as the correct viscosity at a given temperature, and once operating temp (100C) is reached it will be the weight after the "w". I've moved exclusively to 0wxx oils year round, with Montana winters getting down to -35 at times it is IMO pretty much a requirement.
 
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3,557
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I would also look into the MRV(Mini-Rotary Viscometer) number to see how the oil flows(pumpability) at -40C.
 
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