Another Oil Question

[MOturkey]

i read with great interest a thread the other day concerning, among other things, the wisdom of using 15-40 oil in mower engines. I understand the principle of multiple-viscosity oils, but not the chemistry. However, there is one thing I seemed to glean from all this is that the less the range in viscosity the better. In other words, many felt 15-40 oil would be superior to 10-40 because it has to have less additives to accomplish the viscosity change. At least I THINK that is what you guys were saying.

Now, for my question. I've been using full synthetic oil in my mower ever since I bought it. Since 40 viscosity oil is recommended at ambient temperatures of 90 degrees or so and above, I've used 10-40 synthetic, in a couple of brands. Well, the last two times I needed to change the oil, I haven't been able to find any locally. Instead, all the major brands seem to be switching to 5-40 instead, so I bought some Rotella full synthetic in 5-40.

I change my oil every 50 hours, and the other day, with 40 hours or so on the last change, when checking the oil, I found it to be a bit low. Not quite to the add mark, but this is the first time I've noticed any usage between changes (engine has approximately 400 hours on it). It has, however, been hotter than last year, and I operated it in triple digit heat a couple of days, so that may well be a factor.

In the opinon of you guys who really know and understand all this lubrication stuff, is 5-40 OK to use, or should I try and find a source for 10, or even 15-40? I would really like to stay with synthetic oil. They all seem to manufacture 15-50, but since Kawasaki and Gravely don't recommend 50 viscosity oil, I am reluctant to use it, thinking it might be too thick.

Thanks in advance for your help. I'm confused. :confused: :D

[2manymowers]

Amsoil makes a 15-40 in synthetic.

[o-so-n-so]

I run Mobil 1 in most everything I own and have noticed a little oil consumption with this oil. My 2002 2500HD 4X4, 8100 vortex, Allison Auto is the most noticeable. Uses 3 quarts between standard oil changes. :D

[MBDiagMan]

A SLIGHLTY higher amount of oil consumption when using an oil with a Winter range of 5 would be normal.

That said, I would not consider the 15W50 synthetic to be too thick for your conditions. It is a multi grade oil, so it would not behave as 50 weight except at VERY high temperature.

By the way, in the other thread you talked about I pointed out that it is not merely the weight of 15W40 that makes the difference although the narrower span of 15 to 40 does require less VII additive. What makes 15W40 different is that it is commonly the weight of what is called UNIVERSAL grade oil. This oil is designed for diesel engines and as a result has an additive package that works better in ALL engines, diesel or gas. It is a little more expensive than dino oils made for gas engines, but not near as expensive as synthetic.

The 5 40 rotella is a universal grade oil offering you the best of both worlds.

Good luck,
Doc