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Premium Member
2006 Forester XT 5-Speed Manual
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380 Posts
Discussion Starter #1
Hey all,
I was doing an oil change today. After I drained the old oil and when I went to fill with new oil I discovered that I only had 1 qt of Mobil1 5w-30. My wife was out and didn't feel like leaving the car up for a while so I decided to mix the 1 qt of 5w-30 with 3.5 qts of Mobil1 5w-20.

I don't expect it, but are there any issues with this?

BTW- I've got a 2006 XT with a VF-39.

Thanks,
 

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2003 Subaru Forester XS
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167 Posts
Really it'll be better if you pour some water from the garden hose ! 5w20 in that engine is just NO, and especially Mobil one. Put some Red Line 5w30 or Motul
 

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Premium Member
2006 Forester XT 5-Speed Manual
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380 Posts
Discussion Starter #3
Really it'll be better if you pour some water from the garden hose ! 5w20 in that engine is just NO, and especially Mobil one. Put some Red Line 5w30 or Motul
So what you're saying is that tap water is a better alternative than what most manufacturers (Acura/Honda/Ford etc...) call for as their preferred oil? Seriously? If you have a legitimate point it gets lost in that senseless reply.
 

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2003 Subaru Forester XS
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167 Posts
hahaa, i'm saying that oil isnt good for that engine .. . Acura and Honda. . etc engines are made for thinner oils, but still i would not use M1 in them, infact i used M1 5w20 in my accord and got terrible UOA, so my point is - get better oil for that car
 

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2017 VW Golf SportWagen 5MT
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How is your oil consumption with M1 now? Personally I wouldn't run M1 5w20. I wouldn't run M1 of any weight, but that's a personal choice.

You are about half a quart low at 4.5 quarts, I'd be more worried about that.

Stan
 

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Premium Member
2006 Forester XT 5-Speed Manual
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380 Posts
Discussion Starter #6
How is your oil consumption with M1 now? Personally I wouldn't run M1 5w20. I wouldn't run M1 of any weight, but that's a personal choice.

You are about half a quart low at 4.5 quarts, I'd be more worried about that.

Stan
Stan,
I am not married to M1. It is just what I had on hand at the time. I typically use M1 or Castrol Syntec. I will buy whatever I can get locally. (no one sells Amsoil near me)
Actually I did put in 5qts. I was thinking of my wife's car when I said 4.5 qts. So I've got 1 qt 5w-30 and 4 qts. 5w-20. My question wasn't so much about the brand of motor oil but rather, are there any issues to running mostly 5w-20. (4-1 ratio)
My consumption is 1/2 qt per 5000 miles. I have 70,000 miles on the car, (65,000 of which were on the VF-39). Not sure if this is good or bad.
 

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Premium Member
2006 Forester XT 5-Speed Manual
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380 Posts
Discussion Starter #8
Perfect mix for a winter like this!

It'll be fine.
And what a winter its been. I am still sore from my latest gas/electric bill.
I figured that because it is cold the thinner oil would be ok.
 

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05 WRX STI
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200 Posts
Thin oil seems to not be good in Subarus and the ones that say energy conserving are the thin ones! The thin oil causes the engine to consume oil at a higher rate than normal.
Second my local Subaru tuner DOES not recommend any Mobil 1 oil for Subaru's . He has a locked up motor in an STI and says Mobil is the cause.
Third the research I did on the oil consumption issues I had were cured by using the oils with the European specs of ACEA A3 which is specific for turbos.
The Motul 5w40 is what I am using during winter and Valvoline Max Life 10w40 for Summer. 40 weight is good for the turbos heat!
 

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Premium Member
2006 Forester XT 5-Speed Manual
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Discussion Starter #10
Thin oil seems to not be good in Subarus and the ones that say energy conserving are the thin ones! The thin oil causes the engine to consume oil at a higher rate than normal.
Second my local Subaru tuner DOES not recommend any Mobil 1 oil for Subaru's . He has a locked up motor in an STI and says Mobil is the cause.
Third the research I did on the oil consumption issues I had were cured by using the oils with the European specs of ACEA A3 which is specific for turbos.
The Motul 5w40 is what I am using during winter and Valvoline Max Life 10w40 for Summer. 40 weight is good for the turbos heat!
I understand that it may cause more oil consumption and because of that I will probably change it sooner rather than later. (I usually go 5K miles between changes, in this case 3K might do it)
As far as Mobil1 goes, I've been using Mobil1 since 1990, the cars ranged from a 1989 Ford Probe GT (4-cyl turbo) to a 1996 Ford Mustang Cobra (V8 32V). I've never had any issues. I am not saying it is the best, I probably would have been ok with Dino oil. Manufacturers are ok with Dino oil, so I figure even half decent synthetic is a step up.
As for a tuner blaming oil for an engine seizing, I would take that with a grain of salt.
 

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2003 Subaru Forester XS
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If u're so confident that this mix will do, why would u bother asking at all . . .
In my opinion weight 20 is very thin for that engine coupled to that turbo . . . i'm sure most of the turbo guys out here will agree with that
And, Mobil 1 isnt as good, as it used to be, their synthetic is group3, not a real one
It is your car though, so therefore it is your choice . . but i dont think its the right one
 

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99 UK S-turbo
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Just to add that 0W20 is the specified oil for most Subaru's in Europe including the Turbos (and its what I'm running in mine), so I really can't see this being a problem unless your running big mods.

Simon
 

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The Sub kit guy
2005 Forester X & XT VF39
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I've run M1 5w30 in my XT since I got it. I have zero usage issues and my UOAs have all been perfect. I'm well above stock power, make tons of short commutes and live in a hilly area. Pretty much all the things that can be hard on motors.

I personally wouldnt run a 0w20 by choice, but it is winter time and cold in your area right now so I dont think it will be much of an issue as long as you change it before it warms up.
 

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2015 XC diesel CVT
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For what it's worth, while the 0w20 is a recommended oil for many models, the '09 service manual states that it's ABSOLUTELY not suitable for the 2.5l SOHC engine, and will cause "malfunction".
 

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2004 Subaru FXT MT
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1,841 Posts
Considering it was just one quart of 4.5, putting 5w20 in isn't going to cause an issue. Personally, I like to mix viscosities anyhow...

My opinion: My WRX has always gotten 5w30 M1. 141k miles later, with many trips to the drag strip and running 12's, leakdown is great, compression is well within spec. Not saying its the best oil on the face of the planet, but it certainly gets the job done that its supposed to do: protect your engine from wear and damage.
 

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2006 Forester XT 5-Speed Manual
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380 Posts
Discussion Starter #16
If u're so confident that this mix will do, why would u bother asking at all . . .
In my opinion weight 20 is very thin for that engine coupled to that turbo . . . i'm sure most of the turbo guys out here will agree with that
And, Mobil 1 isnt as good, as it used to be, their synthetic is group3, not a real one
I was never completely confident in the mix of 4 qts 5w-20 and 1 qt 5w-30. Not sure if this works out this way but if I average my oil it is 5w-22.
Somehow for you that turned into Mobil1 is harmful to your engine. My question was about running mostly 5w-20 (I almost regret putting in that it was Mobil1). Asking about Mobil1 on car forums is almost like asking a question about a Microsoft product on a computer forum...you will always get someone that will say "Switch to a Mac, MS sucks".
Is Mobil1 the best synthetic? Probably not, but it is readily available everywhere. Now if I can find syntec (pure synthetic...not the blend) I use that.

So when you chimed in with that comment about being better off adding water, I was pretty annoyed. It was of zero help and just your attempt to bash Mobil1. I want to know about the viscosity that I used. (22?). I am good with the weight (5w) and don't want to hear about personal biases against oil manufacturers.

Anyways, from the sounds of it, I feel better about sticking with this oil for 2 months.

Also, a few years back I worked with someone who had previously worked at Mobil. (In Northern Va, before the Exxon merger). He used to give me crap about running Mobil1. Not because there was anything wrong with Mobil1. He told me that Mobil had run their own exhaustive internal tests on synthetics. (Using not just Mobil1 but a large cross section of different synthetic oil manufacturers) They had a bunch of engines setup to test various oils (I want to say they were GM engines, almost like the Castrol commercials). They found that changing oil at less than 5000 miles, all synthetics fared no better than Dino oil. Now at over 7500 miles you would start to see marginally better results. But they found that if you are a jiffy luber (change at 3k miles), there was no benefit to using any synthetic. Suffice it to say, these test results remained internal. I tend to go 5000 miles.

Now, I am not saying that this holds true for Subarus. Especially Subarus with high psi turbos. But I thought that it was interesting.
 

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2006 Forester XT 5-Speed Manual
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Discussion Starter #17
For what it's worth, while the 0w20 is a recommended oil for many models, the '09 service manual states that it's ABSOLUTELY not suitable for the 2.5l SOHC engine, and will cause "malfunction".
I agree with going with a lower weight is risky. I used 5w-20 though.
 

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5w20 is definitely a little too thin for USDM subarus, europe has MUCH better oils so comparison to over there isn't really usable.

The normal (non ep or hm) mobil1 5w30 is already pretty thin and with a tune + bigger turbo 5w20 is not really the best idea. Its probably not going to do anything terrible, but I wouldn't want to run the engine very hard with it in there. Of all the mobil1 oils I've found the 5w30 EP to give me the best results in my XT. The biggest problem I have with oil is fuel dilution, and a thinner oil would make it worse (mostly due to the shorter commutes ~15minute I take to campus).
 

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2007 Forester XT 4EAT-VTD
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Not all oils with the same viscosity ratings are created equal. M1 5W-30 is supposed to be more like 5W-20. That said, I used M1 5W-30 in my WRX for 20,000 miles until I traded it in. I did notice that in the summer, that oil tended to burn off if I drove the car hard - usally a quart in about 4,000 miles.

The last few oil changes on the WRX was with German Castrol 0W-30. That oil held up far better and never required topping off between changes.

I've been running the GC 0W-30 in my FXT for over 55,000 miles and never had to add between 5,000 to 6,000 mile changes.

I think you'll be OK with the M1 5W-20 in the winter, but just keep any eye on the oil level. At the next change, go back to 5W-30.

The synthetic vs. dino oil is another entire debate. For me, changing oil every 5,000 miles, the extra $$ spent on the synthetic is really a non-issue. Over the course of 100,000 miles, the extra spent is a pittance compared to the money I've invested in mods and still only an insignificant fraction of an engine replacement. When it comes to oil, I buy the best and don't give it second thought.
 

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2004 FXT / 2020 Outback Onyx XT
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Most Energy Conserving xW-30's in N. America will have an operating viscosity of a 20 grade oil anyway. Just look up a used oil analysis in any hard driven turbo.

Having said that, I don't run them and definitely wouldn't run them in a modified FXT. I prefer robust oils like Red Line xw-30 and Syntec 0w-30.

Just run the oil to 3,750 miles and do a used oil analysis.
Blackstone Labs
My guess is that it wouldn't look much different than a uoa on Mobil1 xw-30 anyway. High iron, and maybe some other wear metals, and the viscosity probably wouldn't be that much different.

Note that a 5w-20 would not have much of a benefit over 5w-30 in cold weather. The first number is your cold cranking viscosity.

-Dennis
 
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