oil question. .forester

Not unless you have access to the previous service records. But, it doesn't really matter since you will be draining that oil out anyway, and all you need to do is use the correct viscosity for the expected ambient temperatures as called for in the manual. What was used before isn't important.

Hi,

What's in there from the factory is probably an unknown, and most likely always will be!

As Mulder noted, just pick the right weight for your conditions, in a brand you like and can get readily (NO, I'm not trying to start "oil wars" all over again!), and go from there. While lots of us have our own favorites, most of the "experts" I've read over the last 15-20 yrs indicate you can even switch between brands for top ups and such as long as you maintain the proper viscosity. While I try to avoid doing that, I've had to on occasion and nothing bad happened.

Rick

Or you just use synthetic that holds a more constant viscosity regardless of temperature.

More than likely, considering big business, correct viscosity and additives, but lowest bidder.

I got an oil analysis on the factory fill in my 2004 WRX (made in Japan). It was supposedly a 5W-30 oil and still maintained a 30 wt viscosity after I drained it at 3000 miles.

Anywhere from 80-90% of the oil is being drained out anyways. There's very little that can go wrong simply because the type or weight of oil is changed. Most cars are very tolerant of different oils. What's available 7 years from now isn't going to be like what's available today.

I don't know if that's a good way of describing it. Nothing holds a "constant" viscosity. Virtually all fluids thin out with an increase in temperature and thicken when colder. I've heard swimmers describe freezing water as "viscous".

A high-quality **true** synthetic oil (count out most Castrol Syntec or Valvoline SynPower) will still lubricate reasonably well at an operating temp where an equivalent weight conventional oil won't. The viscosity curve is definitely less pronounced.

Most of todays "conventional motor oil" is at least partly "group II/III" oils that some companies (like Castrol USA or Valvoline) market as "synthetic". These are generally better at maintaining viscosity at higher temperatures than their predecessors.

try changing oil outside in January try cranking on a sub-zero degree day

the synthetics flow just as they do in summer but the naturals "flow" like cold maple syrup

Nothing holds a constant viscosity vs temperature, but synthetics come pretty darned close over normal North American temps.

There's nothing "natural" about any modern motor oil. They all use polymeric VI improvers, pour point depressants, detergents, dispersants, and any number of man-made chemicals. In many ways, the terms "synthetic" and "conventional" are marketing terms. Mobil checmists originally wanted to call their product a "synthesized hydrocarbon", and sold their first Mobil 1 offering as "Mobil SHC".

Even in cold temperatures, a 20W-50 "synthetic" oil will flow out of the bottle slower than a "conventional" 5W-20. The advantage of many synthetic oils is that they don't contain waxes that tend to thicken in cold temps. Oil processing has removed a lot of conventional oils and pour point depressants help resist wax crystallization.

Depends on the "synthetic" oil. Many "synthetic" oils these days are primarily group III base oil. Some companies market products based on group III as "conventional". They certain do outperform oils made even a few years ago. Many conventional oils have quite acceptable cold weather performance.

Now - I'm not knocking synthetic oil. I live in a temperate climate but use Mobil 1 5W-30. It certainly is a good choice to withstand the stresses from a turbocharged engine.

changed my oil in my used 98 forester today for the first time. i put conventional 10w-30 in there. i live in so cali, i was gonna go synthetic but i read a lot of stories about how it will expose leaks on problematic older engines. and lets face it. the forester has a very fragile engine. no use in taking the risk. i'll just continue using that oil and change every 3000 miles. the car isnt burning oil at

do u think conventional 5w-30 will be ok for New york winter weather? or will i have to switch to synthetic before i move? what do u guys put in your old subarus? thanks

Works perfectly fine here in western New York; it's the only weight our dealers put in.