- One of the main things to realize about OEM oil recommendations is that they do NOT recommend an oil weight/viscosity (5w-30 in this case) that provides the best wear protection for the engine. OEM’s are fighting to meet the increasing mpg requirements put in place by the government. Using thinner/lower viscosity lubricants can get the OEM’s 0.5-1% better gas mileage. If you look at OEM’s viscosity recommendations over the last 30 years you can plainly see that they used to recommend 5w-30, 10w-30 and 5w-40 and now they are all moving down to 0w-20. There are graphs/data below that show the OEM recommendations decreasing since 2006 and that it perfectly coincides with government mpg regulations.
- My advice is to run a 5w-40 (at least) that is high in zinc. Subaru's run better and burn less oil on a 5w-40 than a 5w-30. This is based on my experience driving Subaru's since 2001, having oil analysis done on my 2002 WRX, 2006 WRX & 2015 WRX's along with downloading & analyzing hundreds of oil analysis sheets.
- Subaru recommends a 5w-30, but as soon as you start using the oil the viscosity begins to degrade/breakdown and by the end of your interval it can have the viscosity of a 5w-20 or lower. This is due to fuel dilution, water dilution and thermal breakdown. By starting with a 5w-40 the viscosity will stay in spec and over 5w-30 levels for the entire duration of its use.
- Many people run Motul 300v 5w-40, Motul 8100 X-Clean Gen2 5w-40, Schaeffer's 5w-40, Brad Penn 5w-40, Joe Gibbs 5w-40 and Rotella T6 5w-40. IAG has reported that they have seen carbon buildup on pistons from cars using Motul X-Cess and suggests NOT using it for DIT applications. Most of these oils have high zinc content which is one of the best anti-wear additives for protecting the bearings. The reason many people run Rotella T6 is that it has equal zinc content to all the above "racing" oils yet it is half the price and is readily available at Walmart, Pepboys, etc. for $20.
- Lots of people get scared of 5w-40 oil because they think it’s worse for cold weather use, but the “w” in the 5w part stands for winter. So the 5w-30 and the 5w-40 have the same cold temp viscosity. The only difference between the 5w-30 and the 5w-40 is that the 5w-40 performs better in hot temps and keeps the viscosity up as the oil degrades through usage. The oil viscosity intended temperature use chart is in the photo slideshow below. 5w-30 is only rated for use up to 95 degree ambient temps. 5w-40 = 104 deg, 10w-50 = 113 deg and 10w-60 = 122 deg. I suggest 5w-40 be used at a minimum and if you live in Arizona, Nevada, New Mexico, Texas or any hot desert climate then a 10w-50 or 20w-50 should be used in the summer. Subaru used to recommend exactly this right in the owners manual (pic in slideshow below), but OEM's are no longer legally allowed to recommend higher viscosity oil than what there government mpg testing was done on. Subaru recommended the use of 20w-50 for hot desert climates, racing and heavy duty use from 2001-2010.
- I did my last oil change on my WRX at 8,000 miles using RotellaT6 5-40. I don’t believe in running expensive oil and dumping it every 1,000 miles. To me that’s just a waste of money. I don’t recommend everyone run 8k intervals, but you can definitely achieve higher intervals if you are testing your oil.
- Base your oil change interval on your driving. If you beat on the car the whole time, change your oil at 3,000 miles…..if you daily drive your car and just get on it occasionally; change your oil at 4,000 miles. Beyond that send off a sample to Oil Analyzers Inc and get it checked to know for sure if you can go for a longer interval.
- The only way you can truly know what’s going on with your oil is to get it tested. It will let you know when something is going wrong. They send you a vile and you grab a sample of your oil and it will show if your bearings are wearing, or pistons, or block, or cams, or if your oil viscosity is wearing down too fast.
The word viscosity describes how easily an engine oil flows.
The viscosity of an oil is measured by its resistance to flow. There are two numbers that define the viscosity of an oil. The first number ends with the letter 'W', which stands for Winter. This measurement is related to how an oil flows when it is cold, such as at engine start-up. The second number is defined by how an oil flows when at higher temperatures normal engine operating temperatures.
The smaller the number, the better it will flow. So a 5W-30 will flow easier than a 10W-30 at start-up temperatures and a 10W-30 will flow easier than a 10W-40 at normal engine operating temperatures. This is important, as engine oils naturally thicken as they cool and thin as they are heated. Thin, low viscosity oils flow easier to protect engine parts at cold temperature. Thick, high viscosity oils are typically better at maintaining film strength to protect engines at high temperatures.
ORDER OF BEST OIL COOLING
- Front mount with air being funneled through the core.
- Top mount with air being funneled through the core.
- Front mount without air being funneled through the core.
- Top mount without air being funneled through the core.
Oil Coolers & "165 degree race thermostats"
- Oil coolers and cooler thermostats are not good mods unless you actually need them.
- The oil temperature is designed/allowed to exceed 212 degrees Fahrenheit to boil off water or possibly other contaminants.
- Combustion is better at higher temps. The lower the oil & coolant temps, the less hp the car will make. I've seen 20-30 whp differences at 160 degrees vs 200 degrees on the dyno.
- Engine wear is increased during cold starts when the oil is thicker, doesn't flow as well and therefore it's lubricating and protection properties are diminished. Adding an oil cooler can increase warm-up time, which keeps the car in a higher wear state for a longer period of time.
- If you live where it snows, you will likely need to cover half or more of the oil cooler core during the winter to stop the oil from being over-cooled.
I only recommend oil coolers and race thermostats for these situations:
- Cars in extremely hot climates that get abused: Cars in Arizona, Nevada, Texas, New Mexico and Florida are more likely to see excessive oil temps due to their extreme climates. I would consider sustained oil temps over 240-250 degrees the point at which someone should add an oil cooler.
- Race cars: cars abused for long periods of time w/ sustained high boost and high rpm where excessively high oil temps become an issue. I would consider sustained oil temps over 250+ degrees the point at which someone should add an oil cooler.
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