does oil "expire"

Additives probably do. Personally I'd use it anyway.

I'd hazard a guess and say that no, it doesn't expire as such. It may well not meet specifications as time goes on, but the oil itself is pretty old (couple of million years at least) and the additives are relatively stable considering what they have to do. And oil dated 2009 isn't that old at all... I've seen, and used, much older oil!

Only if the bottle is allowed to vent and has been exposed to high temperatures (80+ F).

Lynn

Yep. Used to buy a case at a time, usually about a year before it's all used up. Now I buy the big bottles (5qts) and at 6qts per change it takes a while to use up evertying. Think about how long the stuff stays in warehouses or on store shelves.

WTF? Vent? What's that got to do with it--in your engine the oil is 'vented'. High temperatures over 80 F? Goodness, just how hot do you think oil gets in a running engine.

If you had said high temperatures > 220 F for extended periods of time, I'd have bought it, but 80?

Oil that is exposed to air will slowly catalyze (forms longer chains) over a long period. Just take a look at the gummy residue on a bearing from an old electric motor or the inside of a vintage engine. But it takes a LONG time (years) and only the oil exposed to the air converts. I have no problem using a quart of 10 year old name brand oil that has been stored in the factory sealed container for my 4.2L Jeep. I might be a bit fussier for the Porsche race engine though...........

long period. Just take a look at the gummy residue on a

takes a LONG time (years) and only the oil exposed to

oil that has been stored in the factory sealed container

What he said.

Plus the light hydrocarbons will vent to atmosphere over time. I cannot tell you how much the time is but I would not use any lubricating oil that has been exposed to the atmosphere for a "while".

Lynn

Here's another follow on question on oil.

My son has a motorcycle, and his browsing/reading led him to use "Rotella T6 5w40" which is a diesel engine oil - for his motorcyle.... Comments indicating it would hold up better in the high revs engine.

SO - how is this diesel Rotella T6 5w40 different than a car engine 5w30 ? What would happen if you used it in a car engine ?

Different formula for higher temperatures.

engines run a lot cooler than diesel and oilratings are based on the temperature band.

If (big IF) the gas engine maker specifies a 5W-40 (non do that I know of) then it would work just fine probably. Diesel rated oil has better detergent capabilities mostly which are needed to keep the soot in suspension (why diesel motor oil turns black very quickly--not an indication that the oil is bad, either).

However, modern gas engines are not rated for 40 weight oil, and you are likely to damage some parts using the wrong oil. Old engines would probably be OK with it--modern ones much less happy.

As for the motor cycle, I can't answer, you didn't give enough information.

Disclaimer: I am not familiar with that specific formulation of Rotella T.

Folklore back in the 60's for those of us with high revving european sports cars was that indeed the Rotella T diesel oils were superior to the ordinary automobile oils for these engines that otherwise had a habit of burning oil or developing cold engine bearing rattle. The Rotella T oils were listed in the owners manuals as one of many recommended oils.

In any case, Rotella T6 is rated API SM, SL, and SH, and JASO MA, which means that it meets the warranty requirements for just about all cars and motorcycles manufactured prior to the 2011 model year (but do check your owners manual and make sure).

For 2011 there's a new API standard, SN, and it won't meet warranty requirements if that is specified.

Note that the SH rating means that it's also OK for older models that need ZDDP to avoide premature and excessive camshaft wear.

According to my "oil expert" (this is the same guy that gets to do my engines) The diesel oils typically have modifiers to reduce cam lube wear that are missing from the latest SAE oils. So any engine running plan old cams will run longer on either diesel rated or the SH rated oils. After that, I think there is a lot of folklore unsupported by real evidence. The race guys are REALLY into things like that, gives an opportunity for evidence based folk to really take charge.

You've over simplified that statement from the Wiki... Generally (overall) diesel engines in fact run cooler (as they are more efficient) and the higher temperatures are found in the upper ring area.

It is a complex thing, so summarizing it can be difficult!