Switch 5w30 to heavier? 233k

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Nov 12, 2018
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Wife's 03 Subaru has 233k and while me engine wear levels are fine (Blackstone testing 1x/year) I am noticing oil consumption, not leaking. One change I had to hadd .5 qt, another 1.5 qts. I run 5w30 full synthetic. Been thinking of 10w-30, my mechanic buddy said he switched to 25w-50 for his old honda CRX that sucked up oil. seems a bit drastic, but he knows more about cars than I. I know it's an old timer thought to use heavier weight oil to get better sealing, but does that compromise anything else? The tech at Blackstone even said it may quiet lifter noise and be overall smoother.

I also have noticed vibration lately, but don't think that's correlated to the oil levels.
 
10w30 isn't any heavier than 5w30 at operating temp, it tends to be less volatile and more shear stable at least when comparing oils from the same product line. but otherwise will perform pretty much identical. What kind of OCI are you running, losing a quart or so on a 18 year old high mileage engine over the course of an oil change sounds pretty normal to me.
 
A flat opposed 4 cyl may be more prone to oil ring seepage but I defer to any Porsche/Subaru gurus. At that mileage going to a 10W40 high mileage may be a good experiment since it is warming to summer.

Check and change your spark plugs. If becoming oily your O2 sensors and catalytic converter is at risk.
 
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I have owned three Foresters.

Have you ruled out head gaskets? is there oil in your coolant?

If not then suspect valve seals.

If you plan on keeping it up to 400K get the head gaskets done and go thru the heads and install new valve seals.

If you just want to try the 'different oil will fix it' Give Maxlife 10w40 a run

I
 
Changing from 5W-30 to 10W-30 most likely wont change anything as the only thing different is the Winter grade....Still a 30 grade at operating temp....

I would consider a 5W-40 - don't a lot of Subaru owners love using that in their engines anyway?
 
Not a Subaru but for my Tiburon I run a 40wt in the summer and didn't notice it burn any oil but when I went to a 30wt for the winter it burned a quart over 1k so stepping up a grade could help and it's worth a shot going into warmer weather.
 
As mentioned, moving from a 5W30 to a 10W30, you're still a 30 grade at operating temperatures. If there are no oil leaks and the PCV is working properly, I would try adding something towards the end of an OCI like, Kreen, Rislone, or MMO to clean up the ring packs. Run it for 1,000 miles or so and keep an eye on the oil level. Drain the sump and repeat at the last 1,000-1,500 miles of the following OCI. If that doesn't work you could move up to a 0W40 or a 5W40 oil.
 
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