Is 10w30 oil really ok?

10w-30 is not fine unless your average ambient air temp will be no less than 40-50 degrees at startup (even all night at 40 degrees may be pushing it). 5w-30 5w-40 0w-30 0w-40 fine.

 

this can cause more problems if pieces of the hose get caught or ripped which they do. 3.8 is fine.

 

Dude no. What is wrong with sticking with the book weights. I listed them 0w-20 is NOT suitable for LA in any season except the coldest part of winter, unless you want to mess up your engine.

again 5w or 0w, 30 or 40.

 

This is definitely not correct. I believe you are very much underestimating the amount by which oil "thickens" as temperature decreases and the large range of operational viscosity that an engine needs to be able to cope with.

Let us consider the statement that 10W30 requires about 50F ambient before it's suitable, then by that same rational 5W30 would be unsuitable below 43F, which is clearly false. Yes I know you don't believe me, so before you say anything take a good look at this site Graph your oils and compare the viscosity of 10W30 at 50F (10C) with that of 5W30 at 43F (6C). Can you see they're the same!

BTW. Here is a scan from the users manual (Australian) of my 2005 Prius. Notice the wide range of suitable grades as indicated by Toyota, and in particular notice the lower temperature limits applicable to each grade.

 

let me say that chart does not align with what I've seen for the US. Why does the 5w weight has a clear band of application beyond the 7 degree or so difference you indicated that you'd gain? I personally would never even think of 15w or 20w in a prius as suitable -- edit maybe summer time if your ambient air temp is really high. 20w-50 I don't think would be ideal or recommended for a prius at any time by toyota so is this chart is for a prius?

Personally I run 5w-30 synthetic its cheap in jugs from walmart. I have run 0w-20 I didn't like it as much and 0w-30 which runs well too.

I stand by my statement. I would not run 10w as a winter weight in the USA excluding the South. I think your post provides provides a good counterpoint for people to consider though.

 

Please post a reference to where you get 40 degrees. That is silly and completely untrue. 10w30 is fine to 0 degrees F. It may not give the best fuel economy at those temperatures, but it's perfectly safe for the engine.

Again, 5w30 has a much thinner oil than 10w30. The prius wants 30 weight when warm. The 5w30 oil does a decent job of this but does with viscosity modifiers to thicken the oil. The tear and shear characteristics are not as good at the 30 weight equivalent for a 5w30 vs a 10w30.

 

You need to educate yourself more on oils before making those statements. 5W40 and 0W40 oils will be THICKER than 10W30 in above freezing temps.

 

Toyota's recommendation for prius gen 2 in Australia is 5W30 all the way up to 20W50.
USA has CAFE, thus 5W30 only.

 

Yep - we began running 0w20 in our gen II as well as our Lexus SUV hybrid, just as soon as it became available.
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