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118 Posts
Discussion Starter #1
Hi everyone!
This forum is such a treasure of experience to learn from!

So to my question: my wife and I are planning on getting a popup camping trailer and towing with our Forester (see sig). It'll be close to the 2400 lb limit. Anyways, weight is not what my question is about (I've read lots of threads about towing and weights), but it may affect the choice of oil.
We'll be towing in all kinds of places, including deserts in Utah/Arizona, but not always that hot. Also a lot going to the coast and back (over the Coast Range). I'm sure sometime we'll be going over the Rockies.

So I found this in the manual, page 11-12:

- Recommended grade and
viscosity under severe driving
conditions
If the vehicle is used in desert areas, in
areas with very high temperatures, or is
used for heavy-duty applications, use of
oil with the following grade and viscosities
is recommended.
API classification SM (or SL):
SAE viscosity No.: 30, 40, 10W-50,
20W-40, 20W-50
I'm wondering what y'all use for towing, especially if you tow a lot, and/or with high heat or inclines. Subaru gives a lot of different oils to choose from, and I don't know if the 20W-40's enough or if I should go with 10W-50 or 20W-50. Also, what about the classic standard 10W-40 (not on the list)?

P.S. - I plan on putting in synthetic, if it matters.

One more related thought - For the 5MT, I assume I don't need to worry about tranny oil; stock should be fine. Is that a good assumption?

Thanks much!
 

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Premium Member
2008 XS 4EAT
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9,827 Posts
I'll also put this out there. Is a transmission cooler benifical for a manual as it is with an automatic?
 

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2008 XS 4EAT
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9,827 Posts
I'll also put this out there. Is a transmission cooler beneficial for a manual as it is with an automatic?
 

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2003 Forester X Auto
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947 Posts
Castrol makes a 5W-40 synthetic. That's what I used in the summer and for towing my 2K lbs camper.
 

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118 Posts
Discussion Starter #6
Thank you for your replies.

Sounds like I probably don't need to go any higher than 5W-40 synthetic then.
I'll probably do 5W-40 during the camping season and 5W-30 (or even 0W-30) during the winter.
 

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2003 Subaru Forester XS
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167 Posts
Castrol Syntec 0w30 aka German Castrol would be most appropriate since it is pretty thick weight 30 at operating temperature and it is a true synthetic
 

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none none
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I'd actually try a 5w40 or 0w40. I might try the mobil1 0w40. No reason to go for something thicker than the oem specced 5w cold weight.

For the trans I would just make sure you change the fluid regularly (at least every 30,000). Theres no way to run a tranny cooler on the MT as theres no fluid pump.
 

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2009 & Jamboree Motorhome
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347 Posts
Hi everyone!
This forum is such a treasure of experience to learn from!

So to my question: my wife and I are planning on getting a popup camping trailer and towing with our Forester (see sig). It'll be close to the 2400 lb limit. Anyways, weight is not what my question is about (I've read lots of threads about towing and weights), but it may affect the choice of oil.
We'll be towing in all kinds of places, including deserts in Utah/Arizona, but not always that hot. Also a lot going to the coast and back (over the Coast Range). I'm sure sometime we'll be going over the Rockies.

So I found this in the manual, page 11-12:



I'm wondering what y'all use for towing, especially if you tow a lot, and/or with high heat or inclines. Subaru gives a lot of different oils to choose from, and I don't know if the 20W-40's enough or if I should go with 10W-50 or 20W-50. Also, what about the classic standard 10W-40 (not on the list)?

P.S. - I plan on putting in synthetic, if it matters.

One more related thought - For the 5MT, I assume I don't need to worry about tranny oil; stock should be fine. Is that a good assumption?

Thanks much!
We run 10-40 std oil in both our Foresters in Summer when pulling our trailers.. Summer temps run well over 100 F here and we pull 6 to 11 mile 6 to 11 percent grades.. We have had no problems with our 99 or 01 Foresters and run the same in our 09.. I change the oil every 90 days or 3000 to 3500 miles.. And we always change back to 5-30 in the winter..

Snowdance

Flickr: snowdance38's Photostream
 

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I run Mobil1 in our LLBean.

We occasionally tow a Kendon trailer with a loaded BWM R1150RT on it, about 1000lbs total.
Since 1000 miles, I run Mobil1 75w90 in the differentials and I bought the Mobil1 5w40 "Truck&SUV" in the 5qt jugs from Wally World and run that in the warmer months and 5w30 (also 5qt from WW) in our brief Texas winter, which really isn't, if you know what i mean LOL!
FYI - I installed Fumoto valves in both the engine pan and the tranny pan for quick changes. I drain the tranny fluid every 20k and use Castrol Import ATF.

57k quiet and happy miles so far!
 

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09 Forester Limited
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183 Posts
I would suggest Shell Rotella Synthetic 5W40. It's available in jugs from Wallie. In the manual tranny you might want to switch to Red Line in whatever viscosity is recommended.
 

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2009 Forester 2.5X
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216 Posts
I will be towing a 2K+ LB trailer as well in hot temps (AZ, Northern Mexico)I asked the folks at my local Subaru performance shop and they said Motul 10W40. I also changed the rear diff fluid to the Motul (100%) Gear, and for the transmission (5MT)/front diff to a cocktail of Motul (50%) and Shockproof Lightweight (50%). Maybe overkill, but better safe than sorry
Semper Fi
 

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2015 Highlander AWD XLE 6AT
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I will be towing a 2K+ LB trailer as well in hot temps (AZ, Northern Mexico)I asked the folks at my local Subaru performance shop and they said Motul 10W40.
I've done a fair amount of summer towing and camping in that area. My primary tow vehicle is a 3/4-ton pickup equipped with separate coolers for engine oil (oil-to-water, aka OTW) and ATF {oil-to-air (OTA) and OTW plumbed in series}, so I've stuck 5W-30 for year-round use.

AZ and northern NM are, for the most part, stunningly beautiful locations, and we visited this general area (~ Four Corners) while on last summer's road trip. This part of the U.S. is typically at or above 7K feet elevation, so available power from an n/a engine is reduced by ~25% or more.

I agree that towing is a severe duty application. Not only is there the trailer weight to deal with, but the additional aerodynamic drag and trailer tire rolling resistance adds stress to the tow vehicle's drive train even when towing "in the flat".

The combination of altitude, ambient temperature {avg July high in Farmington, NM = 91 F (33 F)}, road conditions (i.e. Glorieta Pass on I-25 "north" of Sante Fe), high-desert head winds (if you're going the "wrong way"), western "speed limits", trailer weight, and increased drag will present quite severe towing conditions.

In fact, it's my view that it's this specific combination of conditions found in the U.S. that is behind some "low" tow ratings compared to those for Canada or Europe (both generally farther north and therefore cooler).

I'd consider bumping up the oil viscosity another notch or two. 20W-40 or 20W-50 will help with cool summer morning starts and provide high temp / high load protection.

BTW, old US 550 from Bernalillo to Bloomfield via Cuba is quite a nice drive. :cool:

HTH,
Jim / crewzer
 

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2009 & Jamboree Motorhome
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347 Posts
I've done a fair amount of summer towing and camping in that area. My primary tow vehicle is a 3/4-ton pickup equipped with separate coolers for engine oil and ATF, so I've stuck 5W-30 for year-round use.

AZ and northern NM are, for the most part, stunning beautiful locations, and we visited this general area (~ Four Corners) while on last summer's road trip. This part of the U.S. is typically at or above 7K feet elevation, so available power from an n/a engine is reduced by ~25% or more.

I agree that towing is a severe duty application. Not only is there the trailer weight to deal with, but the additional aerodynamic drag and trailer tire rolling resistance adds stress to the tow vehicle's drive train even when towing "in the flat".

The combination of altitude, ambient temperature {avg July high in Farmington, NM = 91 F (33 F)}, road conditions (i.e. Glorieta Pass on I-25 "north" of Sante Fe), high-desert head winds (if you're going the "wrong way"), western "speed limits", trailer weight, and increased drag will present quite severe towing conditions.

In fact, it's my view that it's this specific combination of conditions found in the U.S. that is behind some "low" tow ratings compared to those for Canada or Europe (both generally farther north and therefore cooler).

I'd consider bumping up the oil viscosity another notch or two. 20W-40 or 20W-50 will help with cool summer morning starts and provide high temp / high load protection.

BTW, old US 550 from Bernalillo to Bloomfield via Cuba is quite a nice drive. :cool:

HTH,
Jim / crewzer
I agree with the 15-40 or 20-40 or even 20-50 oils.. We have pulled for years with many vehicles.. And when pulling the long grades in high temps when you had a temp gage you would see that heavier oils would lower the engine temp a great deal.. And with an oil temp gage you will also see the oil temp come down a lot.. Subaru uses a cooling system type oil cooler so if you run thinner oil you run the water temp up.. Making it all worse.. For years we always ran air oil coolers but those are seldom found any more..

So we always run at least a 10-40 15-40 or higher in the summer.. But we pull a lot in temps over 100F.. And lots of very long steep grades often down into low gear.. I think the oil I like best for summer pulling are the Diesel oils in the 15-40 grades. We have ran many engines up to 400,000 miles using it in the summers.. Also some car companys are now using diesel grade oils in their gas cars.. VW is one..

There is still no question that the best winter oil is 0-30 or 5-30 depending on where you are..

Snowdance

Flickr: snowdance38's Photostream
 

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2015 Highlander AWD XLE 6AT
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4,255 Posts
Subaru uses a cooling system type oil cooler...
Very interesting! I'd like to learn more about this... any details available?

Update: Found some info here, of course! :icon_wink:

Thx,
Jim / crewzer
 

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Discussion Starter #16
Thanks for all the info!

I decided on Mobil 0W-40, since I've used Mobil in the past with good results, and it was on sale. Also, around here it seems pretty hard to find an xW-40 synthetic for reasons unknown to me, and Mobil was one of few choices.

BTW, we'll be traveling 2 weeks in June, to Utah and Yellowstone/Grand Teton. I'll post how it tows after the trip. :Banane35:
 

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Discussion Starter #17
So on Saturday I had the oil changed and put in the Mobil 0W-40 oil I bought.
The mechanic said "That's interesting. We haven't tried that viscosity yet," with an affirmative tone.

This morning, I was really impressed with the 0W part of the viscosity for normal driving. Instead of the "gravelly" boxer sound in the first minute or so after the usual morning start-up, it sounded as smooth as when warm :banana:. Granted, it's not all that cold now, but has been getting down to mid 40s at night.

I'll post more feedback later, and especially after towing a significant distance.
 

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2010 Forester XT
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A note about running oils like 10/40 0/50, and others with more than a 20 split between the cold and hot viscosity numbers- this especially applies to non-synthetic oils:

The greater the split between cold and hot numbers means that more viscosity extenders have been added to the oil. Viscosity extenders are notorious for shearing in high-temp/load conditions (LIKE TOWING), which means that over time in high stress conditions, the oil will lose its thickness. You can see this by a drop in hot oil pressure.

Because of this, running 10/40 instead of 10/30 can actually reduce the lubrication in your engine, because the 10/40 is less durable oil and can break down faster in the conditions that you need it most.

For that reason, I would stick to a 10/30. I would also use a 15/40 before a 10/40 for the reason above, although I would not do so for the Subaru engines- at least not until they get to 270,000 miles like the EA82 in the car I just gave to my little brother. :)
 
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