weakyota91

I guys i have a 91 3.0 and for the first 4 years i have owened my truck I have ran mobil one 15w-30 motor oil. The last year and a half i switched to 10-30 mobile one. my motor has 175000 miles on the ticker. I was just curious does running thinner oil v.s. the thicker make any difference at all. is one better than the other for higher mileage engines. thanks everyone for your answers in advance. summers here in redding average 110 and winters get down to low 30s

first4runner

they make high mileage oil in 10w-30 and 10w-40? They could make more I dont know, but they make high mileage specific oil.

oops edit: I use castrol high mileage in my 90 runner

TNRabbit

The only real difference in the high mileage oil is that it has a leak stop added (somthing like brake fluid). I'd avoid it unless you have leaking seals.

Thicker oil protects the lower bearings better but sacrifices the upper end in doing so. It's a balancing act.

Keith B.

15W-30? Was there ever such a thing? I recently did a test in my freezer at home: interestingly, 15W-50 Mobil One runs thinner(less vicose) at 0 degrees F. than 15W-40 Chevron Delo.

Mark in MD

I'm trying to figure this out.

According to the guy in the link below, both oils start out at 15 weight. Next come the additives. The oil that will be 50 oil will get more additives than the oil that will be 40 oil. The molecules that make up the additives are curled into little balls at room temperature. Do the molecules curl into even smaller little balls at 0 degrees F? If so, this might explain why the 15w-50 runs thinner than the 15w-40 at 0 degrees F: It has more additives in it.

From the link:

To make a 10w-40 oil, the manufacturer would start out with a 10 weight oil as the base stock. All by itself, this oil would thin out so much at normal operating temperatures that the oil film would be useless. So, they add these very special very long molecules, the VIIs. The VII molecules are as much as 1000 times as long as an oil molecule. The VII molecules curl up in a little ball at room temperature, but as the temperature gets higher they uncurl and stretch out, like a cat sleeping in the sunlight. The more stretched out the molecule is, the more it impedes the normal flow of the oil, thus raising the effective viscosity. Now, this sounds just a little too good to be true. Well, there are two catches: first, these molecules are not lubricants, so the more of them that you add the less oil you have sitting around lubricating things. Secondly, these VII molecules can be broken into pieces by various pressures and forces, like being squeezed through the transmission gears in a motorcycle or the hydraulic valves in a diesel engine. Every time a VII molecule gets broken, the oil loses some of its high temperature viscosity. Synthetic oils made from pure PAOs and/or Diesters typically have very few VIIs, so these oils are far less subject to viscosity breakdown due to shearing of the VII package. As a result, synthetics are far more stable...

http://motorcycleinfo.calsci.com/Oils1.html