I read the owners manual for my wife's car and it says 10w30 for temps 0 and above,5w30 for when temps go below 0....I run RP 10w03 in her car,how low can the outdside temp go before you personally think this oil would be not useable... ..Thanks..
Well, the conservative answer would be 0 degrees F. Does RP publish as Borderline Pumping Temp for that oil? That would indicate the lowest temp it can pump sufficiently, although this spec tends to steadily degrade from the moment the oil's poured into an engine. I'd think that an occasional (but not routine) drop in starting temps slightly below 0 degrees wouldn't be a big issue for this weight.
Well this winter,especially january,proved to be down right frigid with some days not even breaking -2...I was thinking that the oil being synthetic it would handle some below zero weather and still provide good protection,even at start up...Will check with RP and see what the cold pourability is...Thanks for the insight...
Back in the brutal winter of 1978 my truck and car survived a whole month of never going above 0 degrees, and many nights approaching -30. I was running the recommended 10W-30 then. I am sure you see some below 0 weather in Connecticut most winters. At least using the recommended 5W-30 over the winter would give you easier starts and faster oil circulation. A good 5W-30 is easier on your engine in the cold, and still provides good protection to a hot engine. The question is not what can you get away with, but what is best for your engine.