oil consumption increase later in the OCI??

[SuperEd73]

Hi BITOGers,

I'm really not sure why this happens but I definitely notice that my Subaru WRX 2.0L H4 turbo engine tends to eat more oil as the oil ages. What I mean is the engine consumes basically no oil for the first 2,500 miles after a change. Then it starts to eat some as the oil ages. This has been happening for as long as I can recall. I purchased the car brand new. I'm currently running my first OCI of Pennzoil Platinum 5w30 (preferred oil grade as per the manual) after an Auto-Rx clean/rinse cycle using conventional oil. Since that 2,500 mile mark I've had to slowly add about a 1qt of top off oil.

I do plan on doing a used oil analysis in the near future and hopefully that may help answer the question but any ideas as to what may be causing this to occur? Could it be fuel dilution, oil shearing down to a thinner level later in the OCI?

Thanks,
Ed B.

 

[Jim 5]

Originally Posted By: SuperEd73
Could it be fuel dilution, oil shearing down to a thinner level later in the OCI?

Thanks,
Ed B.


That would be my guess. Are you running extra boost or a "chip"? I have read that chipped turbos can richen fuel mapping, which can lead to fuel dilution. Oil shearing over time is common as well even without fuel dilution helping it along.

Have you UOA'd? This would tell you if you have fuel dilution, and would tell you what your viscosity is looking like at the end of your OCI.

 

[TwoWheelRider]

I have a Subaru Forester 2.5L non-turbo and I see the same behavior. No oil consumption until the oil hits 2K miles. Then between 2K and 3K a about half a quart might disappear. I ran Quaker State Synthetic to 5K once only and I had to add 1.5 quart during that time to keep it full.

Subarus are said to run rich by design and they can have fuel dilution problems easily. At least that is what I gathered at the http://www.subaruforester.org site.

Currently I am running an Auto-RX cleaning phase with Pennzoil Platinum 5w30 also. It has another 1K to go before switching to the rinse phase. The engine feels more enregetic already. This is my first ARX treatment at almost 77K miles on the car.

 

[TeeDub]

As the oil becomes more contaminated the quality of your piston ring seal degrades and more oil is consumed. You can actually use this behavior to determine when the oil should be changed under varying driving conditions, once you correlate it to oil analysis data.

 

[RISUPERCREWMAN]

I have seen this with most oils, & on most vehicles I've ever owned! After 2500 miles or so, I have to add a bit.....

 

[bluesubie]

Yes, Subaru turbos do run rich. Try using a more robust oil if you want to curb consumption, espeically since you're at 91k. I've run GC for 7,500 mile OCI's with no consumption. Don't forget that 5w30 is preferred for fuel economy and thicker viscosities are allowed in high temps and in severe conditions.

IMO, you will always have oil consumption running Energy Conserving 5w30.

-Dennis

 

[Gary Allan]

Classic oil fatigue with non-linear consumption. The UOA will tell what's beat in terms of if it's shearing or dilution. One would reason that higher visc would move the onset out a bit further

 

[steve20]

same thing with my 92 Camry- 4cyl.-didn't use a drop until 2K then between 2K and 5K (change) a full quart was consumed-used 6-30 conventional

 

[rationull]

My Civic exhibits sort of similar patterns and the last UOA came backing with high TBN and low fuel. I'd added a half quart of make-up oil in the 6000 mile OCI and IIRC the oil was down between 1/2 and 1 quart when I drained it. I'd expect the make-up oil to up the TBN but not affect the fuel, right?

 

[Jim 5]

Originally Posted By: TeeDub
As the oil becomes more contaminated the quality of your piston ring seal degrades and more oil is consumed. You can actually use this behavior to determine when the oil should be changed under varying driving conditions, once you correlate it to oil analysis data.


That's a new one to me TD. Thanks for posting this. I always learn something when you post!

 

[chevrofreak]

Subaru recommends a 3750 mile OCI for the turbo cars. It makes sense to me.

 

[Jim 5]

Originally Posted By: Gary Allan
Classic oil fatigue with non-linear consumption. The used oil analysis will tell what's beat in terms of if it's shearing or dilution. One would reason that higher visc would move the onset out a bit further

If a used oil analysis showed the oil was suitable for further use, and viscosity was the only issue, maybe a good strategy would be to top up the oil with a heavier weight, like a 20w-50. Presumably when you add that to at least 3-4 quarts (remaining in the sump) of already viscosity sheared oil, you'd get back up to the target viscosity. If you're adding oil anyway, maybe this is the strategy. If you had the used oil analysis viscosity info, you could use the viscosity calculator to figure out what weight of top up oil to add late in the OCI.

It would be an excellent use of a used oil analysis to fine tune your intervals and top-up oil choices.

 

[mechtech2]

My old 320I started using oil at 2-2,500 .

 

[Gary Allan]

Originally Posted By: Jim 5
Originally Posted By: Gary Allan
Classic oil fatigue with non-linear consumption. The used oil analysis will tell what's beat in terms of if it's shearing or dilution. One would reason that higher visc would move the onset out a bit further

If a used oil analysis showed the oil was suitable for further use, and viscosity was the only issue, maybe a good strategy would be to top up the oil with a heavier weight, like a 20w-50. Presumably when you add that to at least 3-4 quarts (remaining in the sump) of already viscosity sheared oil, you'd get back up to the target viscosity. If you're adding oil anyway, maybe this is the strategy. If you had the used oil analysis viscosity info, you could use the viscosity calculator to figure out what weight of top up oil to add late in the OCI.

It would be an excellent use of a used oil analysis to fine tune your intervals and top-up oil choices.


I wouldn't really have an argument with this approach. I'd rather find an oil that could endure the meat grinder a bit better ..but you have to balance the cost:benefit end of it. Linear consumption isn't really a big deal. It bothers us ..but it's mostly a perception thing. Nitpicking, really ..at least over the spans that we typically see. Non-linear consumption tells me that I'm mismatched between the oil selection and the operational conditions (the application over the specified duration of use).

Going to something like a 5w-40 may correct the condition (from the beginning) ..but at what cost ..and to what gain (under the assumption that only viscosity seemed to be lacking in the used oil analysis)?

 

[SuperEd73]

Hi,

I figured I'd answer some questions that came up during the discussion to date.

My engine is bone stock. No reprogramming or other mods performed. I do use Lucas UCL pretty often. It does tend to make the engine run silky smooth at idle. It's also helped my mpgs. My last tank of mixed driving yielded 26mpg. Perhaps a downside of the UCL is it could be getting into the oil and lowering the viscosity.

I will be getting a used oil analysis done on my next oil change which I will hopefully perform this weekend. This is my first OCI using Pennzoil Platinum 5w30 so I'm not sure if I should give it another shot to see if things settle down or if I should up the viscosity on PP or try another oil altogether. Pre BITOG days I was using Mobil 1 5w30 and I was getting similar late OCI burnoff. That was also before I started using the Lucas UCL.

Ed B.