5w30 vs 10w30 wt. oil

The synthetics by their nature are more stable viscosity-wise WRT temperature than conventional oils, and so require the addition of fewer polymers - or even none, possibly. I don't know of any synthetics that for 100% sure don't use any VI improvers, but it's possible that there may be some, esp if the oil does not have a wide viscosity spread (i.e.

10W30 instead of 0W30 etc.)

nate

Exactly! Following the manual, and documenting what you have done, gives you a leg to stand on if your engine burns up and you have to fight to get it replaced under warranty, as in the Toyota and VW sludge failures.

Toyota claimed that most of the failures were due to improper service (even though they seemed to change their oil change interval recommendations after this problem manifested itself.) They were pretty good to replace engines under these conditions.

Of course, VW's idea of warranty coverage is to put a sticker on the gas filler titled "check engine oil." and let the engine leak a quart a week.

I'm confused. If the owners manual says to use 5-30 oil then what would your reasons be to use 10-30 oil. If it will help the engine, please explain how.

I can explain changing oil more frequently than the minimum recommendation. Doing so will reduce the maximum level of contaminants in the oil the engine uses.

They seemed to change the oil interval or they did change the oil interval for the same engine. Big difference.

Yes, considering that Toyota required virtually no documentation of regular maintenance. I believe they required proof of one oil change per year!

If I couldn't find 5W30, I would not hesitate using the 10W30 as long as it had the same API rating.

------------- Alex

Often the owner's manual allows you a range of lubricating oil viscosities which are acceptable for that engine under different driving conditions.

If it does not, and you feel your warranty is in danger, then maybe you want to stick strictly with the manual. (All our cars are now out of warranty. I can run green coolant and even Amsoil if I wanted to do so;>)

I said I would feel no miscompunction. And I wouldn't, but anyone could argue I would be doing the wrong thing.

I feel that the rather minimal difference in the low temperature viscosity specifications in the case cited are all but meaningless. The lower number, IIUC, says that the oil will flow, when cold (unspecified temperature), like a 5 or 10 viscosity single grade oil.

I believe that the upper viscosity rating (30, in this case) is the more important specification in most cases. Some people here (Texas) even go up to higher viscosities (1) when the engine is old enough to have sustained a bit of wear and (2) during hot as hell summers where ambiental temperatures can approach

115F and where you typically may drive at the speed limit for hundreds of miles.

I put much more faith in running with clean oil than in worrying about the differences between the two multigrade specifications that were the subject of this thread.

I'm not sure I agree entirely. Yes, having the upper number "in the right range" is important, since that's the viscosity that matters when the engine is at normal operating temp (ie, most of the time that its running. But on the other hand, the *lower* number is the one that determines what base oil viscosity is used, and the upper number is set by friction modifiers. A higher low number means fewer (or maybe no, in the case of some synthetics) friction modifiers needed to achieve the upper number.

If I start to lose oil pressure at high temperature, I drop the pan and replace the oil pump, or even "roll in" new bearing shells. Thick oil is just a bandaid.

Yep, I agree. 5w30 and 10w30 are interchangeable in my opinion, especially if we're talking synthetic oils.