Snagglefoot beat me to it - Pennzoil Euro becomes 'cheap' when bought on sale and after the $10 / jug rebate.
Switching from 5w30 to 0w30 for the winter months?
- Thread starter TheRuley
- Start date
You would have to look at the spec sheet for each oil and compare the CCS and MRV viscosity numbers. A 0W will have less CCS and MRV viscosity vs a 5W, and a 5W will have less CCS and MRV viscosity than a 10W.
But if you really want to split hairs you start comparing the CCS and MRV numbers between different oils of the same W rating - ie, just compare 0W oils to 0W oils and 5W oils to 5W oils. If you want the very best cranking and pumpability you would choose a 0W grade oil with the least CCS and MRV viscosity between them all. SAE J300 defines the max limits for each W grade - latest version shown below. Of course there are other aspects of motor oils that should be looked at besides just the W rating ... but what I said above would just be focusing on the W rating aspect.
The hardest part of the whole mechanism is getting the cold oil into the pick-up tube. Once it gets there it will make it's way to the pump and be sent into the oiling system.
I always thought this figure was interesting and gives some cold start-up perspective. The oil in the sump is moved in to the pump pick-up by both gravity and by the atmospheric pressure trying to push the oil into the pickup tube when the PD pump is creating a low pressure (suction) on the pickup tube. The moving force due to the atmospheric vs pump suction delta pressure is a much stronger force than just the gravity force.
Seems just the force on the oil due to gravity is essentially tied to the pour point of the oil in terms of how well it moves when cold. If the oil can't flow and fill in the created air void then it can't be pumped. Remember the thread about Ford specifying a lower W grade for high altitude use? Conclusion was because at higher altitude there is less atmospheric pressure, and therefore less driving force to move the cold oil into the pick-up tube during cold start pumping.
Typically the CCS is the limiting factor whether an engine oil gets a pass or fail on a given W grade.
The MRV usually passes at least one grade colder than the CCS.
The theory being and how the W grades were established, that if the engine starts. the oil will pump and flow.
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Yep, the last thing you want is for the engine to crank and start, without the oil being able to be moved by the pump. And look at the viscosity difference at the same test temperatures between the CCS and MRV viscosity in J300. MRV viscosity limits are roughly 9 to 10 times higher than the CCS viscosity at the same temperature. And MRV limits are defined and tested at 5 deg C lower than CCS limits.
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Interestingly, the MRV limit used to be lower with the old testing apparatus.
While on the topic of pour points, I think that gear lube channel points and pour points correlate somewhat.
For example, the 80w140 synthetic gear lube I used shows a pour point if -37C. I feel safe starting and driving the trucks down to that temperature and if it’s colder, I’ll drive very slow for the first mile or two.
Gear and transmission lubes typically don't use a PD pump, and therefore the dP the pump creates in an engine's sump pick-up tube isn't in play in a transmission or differential. So yes, pour point (the ability of the oil to flow just from gravity) would be representative of the oil flowability and therefore lubrication ability in a system where there is no forced lubrication by a PD oil pump.
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