10w 40 motor oil

[murphsubaru]

Is it harmful to use 10W 40 Motor oil in a Forester???

[Twitch de la Brat]

I don't believe so...

Unless of course you're driving in 0* or lower temps.

Then go with a thinner oil, aka 10-30 or 5-30.

 

Twitch

[idosubaru]

Is it harmful to use 10W 40 Motor oil in a Forester???

yes, depending where you put it!

 

for real - no. is there a reason you're asking?

 

be prepared for an oil debate, folks like to spend pages and pages on all sorts of oil idiosyncrasies.

 

frankly the "weight" motor oil you use isn't nearly as important as making sure it never runs low (leaks) and is changed frequently (mileage or time based). whether you use 5w30 or 20w50 or anything in between won't frankly show much functional difference to the average user over the life of the vehicle.

 

if you don't have an owners manual, order one off ebay or post for one in the parts wanted forum here. that will list lots of info like this that will be helpful in the future.

 

good luck!

[OB99W]

Is it harmful to use 10W 40 Motor oil in a Forester???

That depends on how you define ''harmful'' -- to your wallet, using 10W40 instead of the recommended 5W30 might cause a slight reduction in gas mileage. For modern OHC engines, lower-viscosity oil is usually prefered in order to have the cams/valves lubed as soon as possible after a cold start. Unless engine wear is so bad that 5W30 causes problems, it's probably better to use it. However, unless the temperature is very low, 10W40 isn't likely to be ''harmful'' to the engine.

 

 

[...]whether you use 5w30 or 20w50 or anything in between won't frankly show much functional difference to the average user over the life of the vehicle.[...]

10W40 is unlikely to cause trouble under most circumstances, but while the engine's bottom end might not have a problem with 20W50, its top end could. Besides, 20W50 would almost definitely hurt gas mileage to a noticeable degree.

[idosubaru]

i'm not recommending 20w50 nor did i think he would try it, someone concerned with 10w40 probably starts shaking when they're within 15 feet of 20w50 labels:lol:. i've never noticed a difference in gas mileage with oil or synthetic fluids.

 

that being said, i only pay attention to highway mileage as it's the most consistent indicator for me and i drive a lot. under straight highway conditions 20w50 doesn't look much different than lower weights. of course when it's cold it looks like glue! so i can imagine with more cold start and running that could change things.

[lostinthe202]

 

that being said, i only pay attention to highway mileage as it's the most consistent indicator for me and i drive a lot. under straight highway conditions 20w50 doesn't look much different than lower weights. of course when it's cold it looks like glue! so i can imagine with more cold start and running that could change things.

 

+1, I've been using 20w50 in the summer months and 10w40 every other time of year and never noticed a difference in mileage. I also really only do highway miles. I live so far from everything, that if I'm going anywhere, I'm driving 50mph at least.

[greenleg88]

That depends on how you define ''harmful'' -- to your wallet, using 10W40 instead of the recommended 5W30 might cause a slight reduction in gas mileage. For modern OHC engines, lower-viscosity oil is usually prefered in order to have the cams/valves lubed as soon as possible after a cold start. Unless engine wear is so bad that 5W30 causes problems, it's probably better to use it. However, unless the temperature is very low, 10W40 isn't likely to be ''harmful'' to the engine.

 

 

i thought recommended was 10w30. thats what i saw for my 97 legacy. and thats whats been in it since i got it. it was my sisters and she had 10w40 in it but she lives in sacramento.. and now im in rochester.

 

how much difference in gas mileage is likely?

i dont know what it was liek when it had 10w40.. but with 10w30 its really not that great... 25.6 highway max. and ive had as low as 14 mpg but usually aroudn 17-18.

[OB99W]

[...]i've never noticed a difference in gas mileage with oil or synthetic fluids.

 

that being said, i only pay attention to highway mileage as it's the most consistent indicator for me and i drive a lot. under straight highway conditions 20w50 doesn't look much different than lower weights. of course when it's cold it looks like glue! so i can imagine with more cold start and running that could change things.

Murphsubaru indicates his location as Ohio, where winters might be harsh enough for ''glue'' to be a concern.

 

 

 

i thought recommended was 10w30. thats what i saw for my 97 legacy. and thats whats been in it since i got it. it was my sisters and she had 10w40 in it but she lives in sacramento.. and now im in rochester.

Murphsubaru seems to have a '99 Forester (determined from his other posts), so my mention of the recommended viscosity was based on that.

 

how much difference in gas mileage is likely?

i dont know what it was liek when it had 10w40.. but with 10w30 its really not that great... 25.6 highway max. and ive had as low as 14 mpg but usually aroudn 17-18.

I doubt that your gas mileage has much (if anything) to do with running 10W30. My own '99 OB (in which I use 5W30) only gets slightly better mileage than your '97. I don't know if this is true for you, but many of my trips aren't very long (especially in winter), and that will negatively impact mileage for sure. You've probably heard this before, but keeping tires properly inflated (typically a few psi over spec), making sure brakes aren't dragging (corrosion due to road salt can stiffen calipers up a bit), and checking that the front O2 sensor isn't ''lazy'' are some things to consider if mileage is a concern.