2020 WRX oil grade/viscosity thoughts

1193 Views 3 Replies 3 Participants Last post by Bowie base model, 1 mo ago

Bowie base model

Discussion Starter · 2 mo ago

I've got a stock model with stock tune but feel nervous about doing autocrosses with "only" the recommended 5W-30 full synthetic oil. After a 50 second autocross run, the OEM oil temp will rise from the mid 190F's to mid 21xF teens. While the monitored temp should be well within the full synthetic oils transient thermal properties, I don't know how well Subaru rod and main bearings are designed and I am considering moving up to a 5w-40 full synthetic during the summer autocross season.

I switched from my 100% dependable 1998 Plymouth Neon Expresso Coupe with the DOHC/5-sp after 215,000 total (street, autocross and track days) miles with zero engine problems and I'd like to be as fortunate with my WRX.

Your thoughts and recommendations will be helpful.

Thanks

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Trackrider54

· #2 · 2 mo ago

Oil temp is a byproduct of cooling, so adding an oil cooler may be the right move there. Where higher viscosity oil comes into play is if your oil pressure is dropping due to the oil thinning. Keep an eye on the pressure.

I'm old school, so I remember the days when 20W-50 was the preferred weight for performance cars....but today's technology makes thick oil like that unnecessary. In fact, if your engine is designed to run lower viscosity oil, then you may damage your engine if you use a higher weight oil as the oil passages may not be big enough to flow such a heavy oil.

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Gregb

· #3 · 2 mo ago

Bowie base model said:
I've got a stock model with stock tune but feel nervous about doing autocrosses with "only" the recommended 5W-30 full synthetic oil. After a 50 second autocross run, the OEM oil temp will rise from the mid 190F's to mid 21xF teens. While the monitored temp should be well within the full synthetic oils transient thermal properties, I don't know how well Subaru rod and main bearings are designed and I am considering moving up to a 5w-40 full synthetic during the summer autocross season.

I switched from my 100% dependable 1998 Plymouth Neon Expresso Coupe with the DOHC/5-sp after 215,000 total (street, autocross and track days) miles with zero engine problems and I'd like to be as fortunate with my WRX.

Your thoughts and recommendations will be helpful.

Thanks

Im there with Trackrider54. I run a 0w30 Amsoil Signature oil in mine. I do this for cold weather starts. It seems to run well in warm NW Indiana summers. Other than that minor change you stand a chance of causing oiling problems by bumping up the top viscosity number like that. Clearances dictate oil viscosity.

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Bowie base model

Discussion Starter · #4 · 1 mo ago

My 2020 owners manual states:

A. "In choosing an oil, you want the proper quality and viscosity, as well as one that will enhance fuel economy. Oils of lower
viscosity provide better fuel economy. However, in hot weather, oil of higher viscosity is required to properly lubricate the
engine. The following table lists the recommended viscosities and applicable temperatures.
. When adding oil, you may use different brands together as long as they are the same API classification and SAE viscosity
as those recommended by SUBARU."

and

B. "If 5W-30 synthetic oil is not available, 5W-40 conventional oil may be used if replenishment is needed but should
be changed to 5W-30 synthetic oil at the next oil change."

So I am confused by the lack of a clear direction from Subaru:

1. 5W-30 synthetic oil is recommended which I assume means full synthetic oil and then they switch categories.
2. 5W-40 conventional oil may be used if replenishment is needed.
a. Why did they switch between oil types?
b. Why do they exclude 5W-40 full synthetic?
c. How much "replenishment" is permitted? 1/2 quart, 1 quart, 3 quarts? Why is a maximum volume not defined?

and the key statement by Subaru which is the basis of my post is:

3. However, in hot weather, oil of higher viscosity is required to properly lubricate the engine.

How am I as an owner which reads their Subaru owners manual for their WRX interpret Subaru's own statement that a higher viscosity oil is required in hot weather?

Since my oil statement was the use of 5W-40 full synthetic oil vice the 5W-30 synthetic oil:

i. The "cold" weather "viscosity" rating is the same at "5W" for each and "cold oil" is significantly thicker than hot oil so "small oil passages" only come into play with cold oil.
ii. My alternate "hot oil" viscosity increase from "30" to "40" stays within Subaru's "approved" alternate viscosity.

I don't want to drive my WRX out of warranty period on 5W-30 oil only to find out my rod bearings crapped out with less than 200,000 miles on them because they should have been filled with 5W-40 oil?

I rest my case of confusion! LoL

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