WRX Info

Frequently Asked Questions

Engine FAQ: Oil

What is the best oil? Simply put, there is no best oil. While I stand by my premise that there is no best oil, I will offer recommendations as to what I have found are the "best oils":

Synthetic: Mobil Delvac 1 or Lubrication Engineers 8530 MONOLEC
Regular: Pennzoil or Havoline
Synthetic/Regular Blend: Motorcraft

What type and amount of oil should I use? Refer to and use what your vehicle owner's manual requires for your vehicle and engine type. Special Note to Forester and STi owners: The amount listed in your owner's manual is incorrect. The corrected amount can be found via this link. For turbo model Subarus, there has been an important change, please visit this link for details on the new oil types, as well as important changes to oil change intervals that will trump the advice in owner's manual .

Does my new Subaru come filled with a special "break in" oil? No. All Subaru engines are factory filled with: Nisseki-Mitsubishi M1K 5w-30 with no special additives. Note: the manufacturer changes from time to time, but they always use 5w-30 mineral based (non synthetic) oil.

How do I check my oil? The oil should be checked warm. This means your engine has been run enough for the coolant temp level to be normal. The best spot for checking is during fill ups as most gas stations have 100% flat surfaces at the pumps. The distance between the holes equals 1 quart. If the oil level is in the middle of the holes, it is properly filled. The bottom hole equates to 1/2 quart low and the top hole equates to 1/2 quart too full. Keep in mind that you should check your oil several times in one session as occasionally, it will give false readings as the dipstick is a crude instrument for measuring.

A note about oil levels though. As long as you are between the two holes, you are 100% fine. If you are at the bottom hole, add 1/2 quart at your earliest convenience. If you are at the top hole, you can run your car as normal without removing any oil. Once you are outside the lower and upper oil limits, you should become concerned about an immediate removal or addition of oil.

Since I live in Alaska, should my oil weight be different than someone who lives in Phoenix? This is a hotly debated topic since motor oil weights are "designed" for different temperature ratings. There are many oil weight charts that show which weights are "best" for which temperature extremes. The American Petroleum Institute, Society of Automotive Engineers, and nearly every oil manufacturer state plainly that you should use what your owner's manual recommends. API Motor Oil Guide (.pdf document). If your vehicle is used in desert areas with very high temperatures or for other heavy duty applications, the following viscosity oils may be used: API classification: SL or SJ. ILSAC classification: GF-3. SAE Viscosity No.: 30, 40, 10W-50, 20W-40, 20W-50.

How often should I change my oil? Refer to and use the maintenance schedule in your owner's manual. For turbo model Subarus, there has been an important change, please visit this link for details on the new change frequencies that will trump the advice in the subaru.com instructions linked above.

Should I do my first oil change early on my brand new car? Not recommended and not needed. Many users will "violate" their oil change schedule by doing their first change early. The theory is to remove any break in contaminates during the first few hundred or up to 1000 miles. In practice though, contaminates are collected in the oil filter. While not necessary, this is one oil change that many feel much better about doing than not.

Why do some companies or even my dealer always recommend an oil change every 3000 miles? The more often you change it, the more money they make.

What do independent companies say with regard to oil changes and frequency? Consumer Reports tested 20 motor oils over 22 months on New York City Taxicabs. Their results basically stated to use the oil recommend and the change frequency schedule stated in your owner's manual. The full article may be read via this link.

Is it bad to change my oil more often than the owner's manual states? Changing your oil more frequently than required has no negative aspects other than increased maintenance costs.

My car has a turbo, isn't synthetic the best bet for turbos? Subaru turbos are cooled by oil and coolant using a convection system, with coolant handling the cooling needs once the engine is turned off. Older turbo cooling technology relied solely upon oil cooling and synthetics are probably a better bet for those systems.

If I want to use synthetic, when should I switch? This is a hotly debated topic and you will find many convincing arguments for waiting a certain amount of miles or oil change cycles. There is no evidence that one particular time is best, so switch to synthetic when you feel is best, be it at 10,000 miles or 10 miles.

My car has XX,000 miles on it, can I switch over to synthetic? Yes. Some recommend an engine oil flush prior to the synthetic conversion. An engine flush is usually a very thin oil designed to remove old oil deposits. There are many convincing arguments as to whether this step is required or not. Arguably the best engine flush treatment is Auto-RX.

Can I switch from regular oil to synthetic and back and forth willy nilly? Yes. No real reason to, but you can do so if you wish.

What types of motor oil are available? There are three main types:
1. Plain oil AKA mineral based oil or dino oil
2. Synthetic
3. Blends which are a combination of synthetic and dino oil

Are there different types of synthetic? Yes.
1. Group III is a highly processed dino oil.
2. Group IV is PAO (polyalphaolefin) based oil.
3. Group V is an ester, polyolester, or everything else not classified in the other groups.

Which companies make quality synthetic motor oils? Some of the more popular manufacturers are:

Red Line
Mobil 1
Royal Purple
Lubrication Engineers

How do I know what my synthetic or dino oil actually contains? Most motor oil manufacturers have .pdf or html documents listed on their website that contain physical property data and/or MSDS sheets that go over which basestock group it is, additives, and other information about their oils.

Are synthetic blends a good compromise? Yes and no. With commercially available synthetic blends, you have no idea of what the synthetic to dino oil ratio is. One would assume it would be 50/50, but it could just as easily be 10/90. A better and more economical compromise would be to mix your own using a quality dino oil with a quality synthetic. This is an undertaking for more advanced users and should be performed only after careful research.

What about extended oil changes when using synthetics? Extended drain intervals are possible with synthetic oil and some regular oils. To find out at what interval your oil needs to be changed, you need to institute a system of oil analysis. Blackstone Labs provides analysis services to help you determine your oil change interval. Keep in mind that even with synthetics, the oil change interval still should be the same according to the owner's manual. Use of extended oil changes through oil analysis should only be attempted by advanced users, and only after careful research.

What is the best oil filter? Simply put, there is no best oil filter. Popular opinion says the "top filters" are the OEM filter, Mobile 1 filter, and Purolator One filter. For further oil filter information, examine these oil filter studies:

a. Russ Knize oil filter study
b. Oil filter study
c. NTPOG Oil Filter Review
d. Engine Oil Filter Study
e. Armand's Subaru Oil Filter Study
f. LesabreT.com's Oil filter write up
g. Paranoid Fabrication's oil filter expose

These studies, though not all Subaru specific, outline the general characteristics of oil filters for comparison purposes. Visit your dealer or favorite online retailer for the current Subaru OEM filter. Subaru likes to change part numbers every other week, so rest assured your dealer will have the latest version. If you are using an "older" filter, you car is fine and you can continue to use up your old supply until your dealer gets the latest version.

How do I change my own oil? All the necessary tools, tips, tricks, and other oil change related advice can be found by visiting these links:

Scoobymods.com instructions for the Forester.
Scoobymods.com instructions for the Impreza
Scoobymods.com instructions for the Fumoto Oil Drain Valve
A complete n00b's guide to changing the oil in your WRX

Even if your car model is not listed above, these links provide excellent applicable advice for your particular model.

What about engine oil additives such as Slick 50, Duralube, STP, Prolong, etc.? You would be hard pressed to find an engine oil additive manufacturer that hasn't been successfully sued by the Federal Trade Commission. There are also several motorsports and consumer magazines that speak against adding anything to your oil. Here are some articles about engine oil additives:

Article by Chris Longhurst
Consumer Reports article
Snake Oil!
SOA's position on additives

What about magnetic drain plugs or magnets for your oil filter? An oil filter has the ability to filter objects smaller than the human eye can see. If you use a magnetic drain plug, magnets on the bottom of your oil pan, or magnetic devices on your oil filter, they do work, however, they are only holding particles that would normally end up in your oil filter anyway. There is no harm in these devices, however they provide no additional protection.

Any other good articles on oil? These articles may provide additional helpful information:

Engine Oil Bible
The Oil FAQ
Motor Oil Myths
Motor Oil Bible (zipped .pdf file)
Motor Oil by AE Haas

Where can I find more information about oil, oil filters, and other oil related information? bobistheoilguy.com's forum is the best source for this type of information. The folks on that forum eat, drink, and sleep oil information. Obviously there is good advice meeted out on NASIOC, but the folks on BITOG back their advice up with hard data and facts rather than personal impressions.