Should I use a synthetic oil like Mobil one? Is it really any better than regular oil? And I heard once you use synthetic you can't go back to regular oil. would this be the best oil I can use?

how many miles are on the engine?

73,000

I'd probably say just stick with dino oil

Is there any reason why I should or shouldnt?

There is a possibility of the thinner synthetic oil slipping through the aging oil seals... 73k isn't very high, but not new either...

 

I use Valvoline 10W40 partial synthetic in both my cars. I can't say they run better or anything like that, but when I took my valve covers off my Legacy last summer, the valvetrain was spotless, so I'm not going to change something that works. Because of that, I use the same in my XT...

I started using Mobil 1 5w-30 in my 98 OWB when I got it with 75,600 miles on the ticker. I've had no problems since, and have no oil leaks or any other leaks for that matter. I would check out Bob is the oil guy before doing anything. A lot of people use Redline synth in their transaxle and differential boxes, which isn't a good idea from what I've read and heard. IMO switching the engine and tranny fluids to synth is a good plan, but the other fluids I'd suggest sticking with dino.

You can change to syn and back to dino as often as you like. That you can't is one of the 10 main fallacies about syn which just won't die off for some reason. Don't change without doing an Auto-Rx clean to remove contaminants in order to get the max benefit of the M1 or whatever. Rember M1 XW30 is formulated at the low end of the 30W range and I'd be looking for something with a little higher viscosity for summer use IMO.

Mobil 1 is the best engine oil there is. Yes, it may be my opinion, but it is based on many years of experience. 15 years to be exact.

 

I use 5W-50 in summer and 0W-40 in winter.

 

Under extreme heat and load, there is no doubt that a synthetic has the potential to perform, and a mineral oil the potential to break down. This may not be vital to everyone, and I wouldn't urge anyone to pay more for oil than their needs dictate. However, I regularly visit the redline on my tacho, and Mobil 1 lets me do it without feeling guilty

 

I drain and replace every 6k miles, filter included. Playing very safe yes, but many replace at 3k, which is definite overkill.

Originally posted by sprintman

Don't change without doing an Auto-Rx clean to remove contaminants in order to get the max benefit of the M1 or whatever.

 

I found this: http://www.auto-rx.net/index.html

 

But it says it's a transmission cleaner, is it okay to put in the crankcase too?

Thats Transmission medic site but same product. See http://www.auto-rx.com for engine site (there are three in total)

I started using Mobil 1 in our 99 outback at about 70k miles. The car leaks some oil but it hasn't increased since using synthetic. I think the oil is coming from the pan. The seals have never leaked. The engine used noticably more oil with Mobil 1 than the penzoil I was previously using. On the advice of my father-in-law I tried amsoil. The engine is quieter and uses less oil. I don't think amsoil is magical, just that Mobil 1 seems pretty thin. I remember thinking the stuff was water every time I drained it.

 

When I replaced the head gaskets on this engine at 118k miles I was amazed at the cleanliness of the engine. I don't know if it is a fair comparison but this engine was certainly cleaner internally than anything I had ever worked on.

 

The most important synthetic oil characteristic to me is cold start flow. I may even switch my junker over to a cheap synthetic to get this benefit. The increased oil flow at startup when it is near 0 F seems to quiet things considerably. The sound the 2.5 used to make with penzoil and a fram filter at those temperatures made me cringe.

Not so much the Pennzoil (an excellent dino now by the way) but the Fram filter. Cardboard end caps and shoddy anti-drainback valves you don't need if you care for your Sube. And yes M1 5/10W30 is a 'thin' 30W (10.0 cSt @100C). Interesting that the 0W30 is slighty higher in viscosity at 10.3 cSt @100C

I am using the amsoil SDF-20 now. Very pleased with the performance but ouch$$$.

I have OEM from Japan but would definitely use the Amsoil but at a much bigger 'ouch factor' than ever here in Oz. I'm interested in what oils other Subaroo owners use??

Wife's 1993 2.2 Legacy: Chevron Delo 15W40

My 2002 2.5 Leagcy GT: Mobil 1 15W50

 

If I can find it, i'm switching my 2002 to Mobil 1 Delvac 5W40.

http://neptune.spacebears.com/cars/stories/oil-life.html

Delvac 1 is an excellent shear stable oil many regard as Mobil's finest product. Doug Hillary who posts on BITOG from Airlie Beach Qld Australia has Delvac 1 in his Outback , 12 semi's (trucks), and his Porsche. I ran it in my Outback from day of purchase but currently doing Auto-Rx clean and dino a better choice. D1 is CI-4/SL rated, oils don't come much better than this IMO.