I just picked up an 04 3.0 Outback with 147k and I thought it might be a good idea to move up to 10W-40? Not sure if the past owners used syn. oil or not.

 

Thanks guys,

 

Dave

The best way to get high miles is to keep using the same ol same ol.

Whatever the car manufacturer recommends for weight and you will be good. Anything else, disrupts natures course.

Look around in and on the car for any oil change stickers stuck on the corner of the windshield or on drive's door jam, also maybe a receipt in the glove box to see what previous owner used for oil.

 

On cars over 100K miles, I use 10w40 in the cold winter months, 20w50 oil the rest of the year with no problems. I learned this advise from a mechanic some time ago, and have no problems. The adage is that the heavier weight oil lubes better in an engine that has many miles, and thus some wear on the piston rings and cylinder walls.

No. The bearing clearances are not appreciably different at your mileage. In fact they never really change much unless one is about to give out. The oil viscosity called for is based on the oil pump and gallery sizes more than anything. You will cause more problems than you will solve with heavy oil. While it may cause less oil burning - that effect is less about the rings not passing the heavier oil and more about the cylinder walls not getting as much lubrication as they did before - the cylinders are lubricated via "sling" from the rod bearings - heavier oil doesn't sling as far or as much.

 

147k is nothing - I've torn down Subaru engines with 250k that still have the factory cross-hatch in the cylinders and no appreciable wear to the bearing inserts.

 

I would not go to synthetic at your mileage. Not unless the engine has been meticulously maintained. And even then I would flush it out first.

 

GD

Edited March 16, 201016 yr by GeneralDisorder

if you use thicker oil on a 4 cylinder that is not worn, the oil will be too thick to get to where it needs to be. Like GD said, you are probably causing damage.

Subaru engines don't start showing wear til after 300k, and even, then, use the recommended weight oil. If we are talking V8's Big blocks, etc. then what you are doing would maybe be okay.

Agree with GeneralDisorder and bheinen74. Stick with the recommended grade; going thicker hurts lubrication rather than helping. Also, if you change your own (or even if not), it would be preferable to stick to the same brand as well. Not as important as other things, but helpful for wear.