I have been reading on this forum about the different motor oil they use and Im slightly confused. I have 2002 WRX it has about 69,000 miles on it. I have been reading that the recommend oil is Synthenic Oil, is that true? 5W30 OR 10W30? I know it says in the manual ethier but I would like a honest answer for you pround Subaru Owners... So please help me out. I know there are many post on this issue but I can't get a straight answer. So please help me out. Thanks!

 

I don't recommend or use synthetic. Conventional oil at the weights and quality specified is the cost-effective choice. Oil and filter changes between 3 and 4K miles. Like the manual says, 5W-30 is the default with other viscosities recommended for certain temperature or driving conditions.

 

ok, so what about 10W30?

 

For my 03 WRX Sedan, 10W-30 is one of the viscosities Subaru recommends in climates where the low temp is above 0 F and the high is over 100 F.

Take a look at the oil recommendation page in your manual. If it says 5W-30 is good for the temperature ranges you will be operating in, then use it. You will get the best gas milage with 5W-30.

I use 5W-30 most of the year, but run 10W-40 during the summer because of the 90-100+ heat. I sacrifice a little MPG in the summer for the better lubrication qualities of 10W-40 at high operating temperatures.

 

I use 10w-30 because the 5w-30 is ONLY about fuel mileage, and not for engine longevity IMO!

I did try synthetic Mobile 1 5w-30 around 5k miles and it seemed to thin, later switched to 10w-30 Mobile, and now run a 10w-30 conventional/synthetic blend.... like that the best.

 

I used to worry that the 5W-30 was part of a MPG conspiracy too, especially since the turbo car I ran for 260K miles was run on conventional 20W-50. Then I started to noodle it through and decided that both oils and engines have changed a lot during the last 15 years and I was going to follow the manufacturers recommendations. When it comes to their cars, Subaru seems to be right virtually all of the time.

 

Yeah, not totally convinced one way or another, but I noticed much more engine noise when cold running 5w-30. This noise is much easier to discribe in an integra or something, where you get a lot of cold valve noise, and even in my old integra, 10w-30 or thicker seemed to quiet that noise. If it's quieter, that means the oil is a better cushion, right?

If this doesn't seem intuitive, look up the valve adjustment specs on a honda or acura motor... the cold measurement is much larger due to how metal expands when heated.

 

I use synthetic in my WRX because it tolerates more heat before breaking down when compared to traditional dino oil. Turbo makes a lot of heat, therefore I use synthetic. Overkill? maybe. But I spend less to change my own oil with synthetic than I would if I paid someone to put Penzoil in my car.

FWIW, I run 5-30 in the winter (I make a lot of trips to the snow) and 10-30 in the summer. My car consumes no oil and runs great.

 

Anyone who changes their own oil & filter at the right intervals gets a thumbs-up from me, regardless of the synthetic/convential oil issue.

Garage oil-changers save a huge amount of $$$ over time and don't have to worry about a botched job at the quick-lube. Back when Mobil 1 was beginning to get popular in the early 80's, I had a friend who bought a new beamer and bought a 40-50 gal drum of the stuff to keep in the garage. He had the hand-crank pump and everything. Some serious savings, there. I know some farmers who do the same thing.

I buy my convential oil (Castrol GTX) by the case and only when it's on sale. I keep the garage stocked a couple of cases ahead. Not as cheap as buying by the barrel, but not bad.

Yep, a cold engine seems to make more noise when run on the thinner oils, but OTOH the thinner oil will circulate and penetrate quicker in a cold engine than the heavier oil.

Pennzoil ain't bad. I use Pennzoil or Quaker State straight 40W in the boat engine. Talk about simple tech, that engine is a Chrysler Marine M-7, a 120 HP 250-inch L-head six that's a stump-puller. 200 lbs torque @ 800 (yes, 800) RPM. Built in 1947 and only weighs 840 lbs. Red-lines @ 2700 RPM.

 

Synthetic oil Polyalphaolefin (like Mobil 1) or Dibasic Organic Esters (like AMSOIL) have real benefits in applications such as gas turbine engines (for which they developed) but in turbo-charged gasoline-fueled cars like ours they represent a non-recoverable "overkill" expense. The only advantage of synthetic vs. conventional in our cars is that the synthetic oils will not boil off up to a maximum of 20% volume during the 3-4K useful life of either oil. Conventional oils with state of the art (turbo approved) additives (which are also found in the synthetic oils) bear an API service rating of SL, whether or not they are synthetic, "dino oil" or peanut oil (just kidding). It's all about SL.

 

A few days after reading my last post there is something I want to add. The API (American Petroleum Institute) service ratings are for passenger car use. They also have ratings for other classes of uses, but nothing else that's pertinant to our cars.

If I were autocrossing or racing my WRX a lot, subjecting it to conditions where that turbo starts to glow a lot, the oil temp really starts to soar and the oil starts to boil off faster than the rate of 20% of volume in 3-4K miles, I'd switch over to synthetic without hestitation.

But, I'm not racing or autocrossing. Even when I'm "driving the twisties" I don't put that kind of heat into the engine. There's plenty of time for the turbo and oil to heat-cycle.

If you are not racing but are a very demanding driver with conventional oil in your engine, you might want to consider the synthetic oils if: your engine doesn't leak or burn oil, but more than a quart of oil mysteriously "disappears" in 3-4 K miles.