ive been hearing some things about how 10-w40 is good to use in subarus? is that true? cuz the oil cap says 5w-30 but i heard that using 10-w40 makes it last longer or something? im not sure but any help from you guys can help!
thanks!

 

your motor oil acts as a thin film of lubricant between your gears so your gears don't rub. The higher the viscosity of your oil, the better it is for hotter days, since the viscosity will drop as temperature rises. If you're using too thin of an oil for hot days, your gears will have a higher chance of rubbing and lose torque also. If you're using too thick of an oil for the outside temperature, your car will drive pretty sluggish and use a ton more gas.

to really answer your question: though it says 5W-30 on the cap as an all around motor oil. I would not use it on a 90degree day in the bay area since the viscosity is too thin and the car loses torque; and engine wear and tear will happen. After my trials with many viscosities, 20W-50 is great for summer use and 10W-40 for winter time. For snow, I would use something with even less viscosity according to the temperatures im hitting. Hope those two viscosities can be a starting point to test what you enjoy driving with and adjust from there. Never hurts to have too thick of an oil, but too thin will definitely kill your engine. my spare 85 stock toyota pickup with original motor and transmission with 400k on the clock can still hit 110mph on daily basis and *no lie,* run with a first gen miata on the freeway up to 90mph. pretty impressive if you ask me; and i've shamed many 80's and early 90's 'ricers' with my pickup. motor oil makes or breaks your engine's performance, i can't stress enough to people that one of the most important things to invest in for the car is quality fluids that your car runs on.

personal tip: if you purchase massive amounts of Redline Oil from the distribution location in Benicia, they cut you a good deal. =)

-hope this helps. Goodluck

Redline FTW

 

for what its worth, i use rotella T 15w40 in my wrx in the summer. i have 2 UOAs on that oil and they were very good (the car was tracked during 1 of those 2 oil changes as well)

 

i use 0-30w Castrol European formula. many users on "iwsti" have done their own oil anaylasis and results have shown this oil performs well.

so if you want to be sure your oil is doing its job well send out an oil sample to "blackstone lab" and they can test it for abnormal wear, metalic pieces, and moisture etc..

 

o thanks for the info guys!

 

Oil lubrication is most sensitive to oil viscosity, which is what the xxWxx spec refers to. Personally if you're worried bout engine longevity then just stick to recommended oils for summer/winter use. Engine manufacturers know best which oil to use as they have worked this out using tribology theory. Have a read about hydrodynamic lubrication. Too thin an oil and you'll start losing oil film between rotating surfaces (ie big end bearings etc). You might gain some performance from less lubricant resistance but which are you chasing? Performance or longevity?

As for oil analysis, it good if you take continual periodical oil samples and get them analysed to form a normal trend so you know when something starts going wrong. A one off oil analysis won't give you a go/no go answer regarding oil suitability. A one off test (if off the scale) will only tell you that you've worn/broken something since the last oil change, well after the fact and well past the point when you can do something about it.

Anyway stick with the recommended oil and change it out regularly to keep it clean and within it's viscosity spec. Oil thickens up due to oxidisation, something that’s accelerated with higher oil temps (ie harder driving). This is where synthetic oil comes in, as it’s better at resisting oxidisation thus can be changed out at double the intervals of dino oil. Hope that helps

 

thanks man!