Does a 5w conventional start as well at -20f as 5w synthetic?

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At -20°f yes. I'd say that they're very similar. It's when its even colder e.g. -30°f or-40°f that a synthetic oil would be showing its benefits. Other ways too but you're asking specifically about cold temp starting.
 
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Originally Posted by Char Baby
At -20°f yes. I'd say that they're very similar. It's when its even colder e.g. -30°f or-40°f that a synthetic oil would be showing its benefits. Other ways too but you're asking specifically about cold temp starting.


Wouldn't you be looking for a 0w for anything colder than -30f anyway?
 
Look at some product data sheets. Some brands show their viscosity at -30 C and you can see generally lower viscosity for a synthetic which likely would be easier cranking for the engine.
 
Originally Posted by Whammo
Originally Posted by Char Baby
At -20°f yes. I'd say that they're very similar. It's when its even colder e.g. -30°f or-40°f that a synthetic oil would be showing its benefits. Other ways too but you're asking specifically about cold temp starting.


Wouldn't you be looking for a 0w for anything colder than -30f anyway?


Absolutely!
Two vehicles in my sig(Altima/Civic) are using 0W20 oils and we're only getting down into the teens and maybe down to Zero overnight. But, we're using 0W20 for other reasons than just outside temperatures.
 
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If it's very cold and your battery is weak, I would prefer synthetic of the same grade over dino even if within the W spec.
 
NO. Mostly ...

The 5w winter rating means that the oil does not exceed a maximum viscosity in two very cold tests. A good synthetic 5w30 will often easily beat the 5w criteria, and almost meet the 0w criteria ( 5*C colder ) .

A conventional 5w30 will sometimes BARELY meet the 5w criteria, and not even come remotely close to meeting the the 0w criteria. Usually the cold temp cranking test is the harder criteria to meet.

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Using Pennzoil as an example ... the 5w30 PUP is noticeably thinner ( less thick ... ) at extreme cold temps than is the PYB HM. Yet both meet the 5w winter rating criteria. Realistically, if the oil can pump, both will work about the same. But it will take more energy to crank the engine with the thicker oil. And if your battery is only gonna give you one shot at starting, the synthetic will pump easier.

The conventional Pennzoil HM yellow bottle 5w30 is as follows:

[Linked Image]


Pennzoil Platinum Ultra synthetic 5w30 is as shown :

[Linked Image]
 
Full synthetic lubricants and greases are the only way to go in really cold climates (like my Alaska).
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The advantage will go to the syn especially when well into the oil change interval.
 
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