Engine flush - pros and cons, Subaru 2.5L turbo

[Kamen]

I just purchased a Subaru Outback XT, with the 2.5L turbo engine, which is notorious for having the turbo charger overheat. The direct reason is the oil starvation caused by clogged inline screens in the oil supply lines leading to the turbo. The latter being caused by infrequent OCI. The previous owner believes they have changed the oil regularly, but they have kept records and in those records there are two lapses of over 10,000 miles.
While I am getting some advice at the LegacyGT forums, I was referred here for oil-specific questions. I had an engine oil analysis done and the results are posted here:

The concern is that if the oil running through the turbo is mostly used for cooling and not lubrication (couldn't get an answer to that), then any wear on the turbo shaft would not be reflected in the test results. However, while I plan to inspect those inline screens, I am wondering if I should do an engine flush, and if yes - what product and procedure is recommended here?
Kamen

 

[Astro14]

Oil analysis looks good. I don't really understand your concern...cooling vs. lubrication? If you don't have enough oil going through...you think there won't be wear?

Either way, I am not a big fan of flushes, though I did them with OHV V-8s decades ago, I think they cause more trouble than they're worth. If you're worried about clogged screens, the best remedy is to remove and clean/replace those screens...more work, but much more certain results...

 

[HM12460]

Don't think I would do a flush. The oil going to your turbo is very critical, and IS used for lubrication. A flush would be detrimental to the bearings. Definitely inspect your screens for peace of mind. I betcha they will be in better shape than you are thinking!

 

[Donald]

Welcome to BITOG.

I would use a quality synthetic oil like PP or PU that is the proper weight called for in the owners manual. Its excellent oil and a good price at Walmart.

The oil certainly lubricates the turbo, as it spins at high RPMs. And cools it.

The UOA (should always get TBN) will show wear metals from every place the oil runs through, so both engine & turbo. It would be hard to determine wear metals from the turbo vs engine. Unless there were some odd metals used in the turbo.

I assume the filter has a lower micron rating that the screens to it should always pick up the particles in the oil and none should clog the screens. Thats the theory. I would certainly check the screens if its not a big deal.

Turbos get coke deposits which is a hydrocarbon heated in the absence of oxygen. Mainly from quickly shutting down the engine when the turbo is still spinning. No more lubrication or cooling.

A quality synthetic oil will clean the engine slowly which is what you want. Forget the flush.

 

[Turk]

Originally Posted By: Donald
Welcome to BITOG.

I would use a quality synthetic oil like PP or PU that is the proper weight called for in the owners manual. Its excellent oil and a good price at Walmart.

The oil certainly lubricates the turbo, as it spins at high RPMs. And cools it.

The UOA (should always get TBN) will show wear metals from every place the oil runs through, so both engine & turbo. It would be hard to determine wear metals from the turbo vs engine. Unless there were some odd metals used in the turbo.

I assume the filter has a lower micron rating that the screens to it should always pick up the particles in the oil and none should clog the screens. Thats the theory. I would certainly check the screens if its not a big deal.

Turbos get coke deposits which is a hydrocarbon heated in the absence of oxygen. Mainly from quickly shutting down the engine when the turbo is still spinning. No more lubrication or cooling.

A quality synthetic oil will clean the engine slowly which is what you want. Forget the flush.


Agreed.

 

[Voltmaster]

unless your oil keep getting really black fast continuously i wouldnt recommend it.

I am sure amsoil's flush doesnt hurt it , but too much of anything including detergent is bad.

Oil analysis looks good , use higher quality filter like mobil1 bosch extended or something similar to clean up the [censored].

Penzoil HE series promises up to 30grams of trapment for example.

 

[LeakySeals]

Starts with me. Kreen. Not sure you need it though.

 

[Hollow]

No flush. Your owner's manual even recommends against it.

You want a synthetic oil and change it under 5000 miles. Subaru revised that vehicle's OCI down to 3750 miles, as it was cooking with conventional oil and up to 7500 mile intervals. The good news is pretty much any API rated oil will be fine for that interval. QSUD is a great value for the price. Rotella T6 5w40 also does well in Subaru turbo engines, along with Mobil 1 0w40.

Would also suggest a Subaru or Wix filter for the correct bypass specs, as Subaru OEM has an unusually high bypass.

 

[Kamen]

Thank you all for the thorough and authoritative answers. I'll make sure I understand your advice before I follow it, though.

First, my concern about the relevance of the UOA to the turbo problem was started at the LGT forum when they suggested that UOA wasn't a good indicator of whether the turbo was worn. Since I didn't get a response, I speculated that the turbine shaft, which is what would get worn, might not be one of its parts that are bathed in oil. If it is and was worn, one would think that any abnormal wear would show up in the UOA. I realize one cannot be sure but if shaft wear is supposed to show in the UOA, it being clean would be an indication that the turbo is in good condition.

Second, I will check the filter screens, although it is a very tedious and difficult operation (for someone with large hands, like me) and it is very cold outside these days. I'm just afraid to drive the car until I'm able to do that. Maybe I'm worrying too much.

Third, I'm glad you are suggesting against an engine flush - I never liked the idea, either. I've only done that on my old T-Bird, and it was right before an engine rebuild (it did not help). I will use only good quality synthetic oil, which is what I have been doing on my 155K-mile turbo Impreza. Just one question: I've been using Mobil 1 on it, is Pennzoil so much better?

Fourth, once I start driving it, I will monitor the oil (UOA and TBN - I didn't get TBN on this sample because it was taken much before I had decided to buy the car) to determine the ideal interval but mostly to monitor the health of the engine. In either case, I will not let it get dirty, hence my next question: why not the OEM filter? I have used Subaru filters (not just oil) on all of my cars (they are all Subarus, including a 300,000-mile Legacy) and have been quite happy with it. When you say it has inadequate bypass specs, do you mean that it will bypass too early or that it will bypass from the beginning? Before I forgo an original part for aftermarket replacement, I'd like to understand the reasoning behind it.

I appreciate the feedback and hope to be able to make good use of it.

Kamen

 

[bluesubie]

I'm surprised I missed this at lgt.com.

A blockage of sludge in the oil screens will likely not show up in a uoa. It didn't in mine and I've done a lot of them. You're getting Nitration results (as did I) which may help in picking up the formation of sludge (from what I understand), but the lab did not flag my uoa at all only 1,500 miles prior to a turbo failure. My lead did jump to 10, but the lab didn't comment on that either. I had the infamous P0011 and P0012 just before the failure.

I'm pretty certain that your owner's manual does not recommend against using a flush. In fact, SoA has a TSB recommending their own flush:

http://www.scoobymods.com/showthread.php/tsb-02-110-10-engine-13825.html

The head tech at my dealer convinced me to keep my screens in because he felt the benefit of keeping them in (to block debris), outweighed the benefit of removing them. To help prevent a blockage from sludge, I would run a robust oil (i.e. not Resource Conserving 5W-30), check the oil level weekly, and keep the intervals at a maximum of 5-6k miles. With an RC oil, I would follow SoA's 3,750 mile recommendation.

-Dennis

 

[Clevy]

Kamen
If comparing pennzoil platinum and Mobil 1 I would say they are on par with each other,and if you are using Mobil 1 right now I doubt very much you will have any sludging issues.
Pennzoil ultra has better base stocks than Mobil 1 however I doubt very much they would be much,if any performance difference.
Now if you were deciding whether to use Mobil or pennzoil I suggest buying whatever is on sale at the time,since they are so closely matched.
As far as a flush is concerned I suggest talking to your dealership about that. Flushes and turbo's don't always work well together. Have the dealer do it if required and then if any issue arises they are on the hook for it.

 

[tig1]

Since you have no evidence of turbo problems I would not use a flush. You ask is PP is better tham M1? I can't speak for Penz but M1 was the oil Honda chose to lube their turbos with the HTO-06 high temp low deposite spec. I would use M1 5-30 which has that spec. For sure all M1 oils keep engines very clean and am sure it will be fine for your turbo as well. I would have to respectively disagree with Clevy about the base stock of Penz being better than M1, but no doubt PP or PU is a fine product.

 

[cptbarkey]

like others have said, 10k OCI on a turbo subaru is definitely NOT ADVISED. drop it down to 3750 or 5000 at the MOST.

 

[skyship]

Originally Posted By: Kamen
I just purchased a Subaru Outback XT, with the 2.5L turbo engine, which is notorious for having the turbo charger overheat. The direct reason is the oil starvation caused by clogged inline screens in the oil supply lines leading to the turbo. The latter being caused by infrequent OCI. The previous owner believes they have changed the oil regularly, but they have kept records and in those records there are two lapses of over 10,000 miles.
While I am getting some advice at the LegacyGT forums, I was referred here for oil-specific questions. I had an engine oil analysis done and the results are posted here:

The concern is that if the oil running through the turbo is mostly used for cooling and not lubrication (couldn't get an answer to that), then any wear on the turbo shaft would not be reflected in the test results. However, while I plan to inspect those inline screens, I am wondering if I should do an engine flush, and if yes - what product and procedure is recommended here?
Kamen


Good to hear the rest of the posters saying don't flush, as that is the best answer. The UOA looks real good although there are no universal averages listed and it would be interesting to know which oil and OCI the UOA was for.
If the turbo goes bad it will probably show Cu and Fe and 2ppm of Cu is nothing to be concerned out. Bad turbos nearly always start to drip oil after high RPM use, so if it looks clean underneath it is probably OK.
The forum chaps will know more than most about this engine, but it sounds like a major brand full synthetic that has lots of Calcium detergent and Boron dispersant compounds will help keep the engine clean. If you change that type of oil every 5K miles (Check the Subaru service schedule for the OCI, as the oil filter might be good for 10K miles) and don't sit in traffic jams or go off roading in dusty conditions the engine will stay clean (The UOA does not list an insolubles figure for some reason).
If you do get definite evidence of a potential sludge issue, like the oil turning black immediately after an OCI, the oil pressure warning flickering at hot idle after a high RPM run (Serious) or lumpy stuff in the old oil (Even worse), then get the sump removed to see how bad the problem is and clean it out along with the oil pump feed screen. If it's bad then unfortuntely the head will need to be removed for a major cleaning job.
I might be known by some as an anti snake oil type, but I regard idle only flush oil additive as a safe maintenance product. The two brands that seem to be of the best quality are Liqui Moly and Amsoil, probably because they are real engine oil companies. You add the flush just before the OCI and let the engine idle for 10 or 15 minutes and then change the oil and filter. This is the link to the data sheet:
IDLE FLUSH
Watch the oil pressure light during the 10 (LM) or 15 mins (Amsoil time) the engine is at idle and NEVER DRIVE AROUND WITH FLUSH ADDITIVES IN THE OIL. These types of oil additives are safe because even if the oil filter blocks or the turbo feed line got obstructed as 10 mins at idle will not do any damage to the engine.
I will now take cover before some chap says poor a can of Moo oil in and drive around for a few weeks, don't even think about it!

 

[Clevy]

Originally Posted By: tig1
Since you have no evidence of turbo problems I would not use a flush. You ask is PP is better tham M1? I can't speak for Penz but M1 was the oil Honda chose to lube their turbos with the HTO-06 high temp low deposite spec. I would use M1 5-30 which has that spec. For sure all M1 oils keep engines very clean and am sure it will be fine for your turbo as well. I would have to respectively disagree with Clevy about the base stock of Penz being better than M1, but no doubt PP or PU is a fine product.


I'm not arguing as I have no actual data however from what I've learned here pennzoil ultra uses a higher margin of group 4 basestocks that regular M1,the EP line and afe line do have a higher percentage of group 4 however I don't really think there would be much of a perceptible performance difference on a short drain interval like 5000 miles. Tig has hundreds of thousands of miles using M1 under his belt and that kind of experience is tough to argue against,so I'm not going to disagree with his point as he has experience using the exact same product,whereas I rarely run the same oil for consecutive runs.

 

[Trav]

Skyship.
Don't flush, that the right answer but use the flush i recommend?
Are you serious?
Skyship give it up, people are not buying into your nonsense.

OP I agree for what that's worth about not using any flush idle or otherwise.
Cleaning the screens sound like a good idea then just use a good synthetic like Mobil 1 EP or PU.

 

[Kamen]

Thank you all, again. Now that I have purchased the car and obtained the maintenance records from the owner, I have some additional information about the oil type and the OCI: the OC was done at a local Subie shop (not a dealer, but they only do Subies) and is listed as "Castrol 5W30 bulk", and the mileage between the OC and the analysis was around 4600 miles. I think the numbers in the UOA now look even better, knowing that it had that many miles on it.

At this time I'm still debating whether I can drive the car for short distances if I were to only do an OC with Mobil 1 10W30 and a Subaru filter, until it gets a little warmer and I get to inspect the filter screens, the turbo and do another OC. I mean, short of blueprinting the turbo, is there any way I could ever have a guarantee it's all good?

Kamen

 

[Trav]

If there are no obvious symptoms like excess oil consumption, noise from the wheel touching the housing (scraping noise) and performance is good then chances are good the turbo is okay.

You could remove the intake side plumbing and check for axial play (there should be none that can be felt), there may be slight radial play which is normal.
See if there no oil present. If you are not having any noticeable issues there isn't much point in going this far though IMO.

Mobil 1 0w40 and PU seem to be the best at cleaning, regular Mobil 1 isn't exceptional at doing anything but maintaining the status quo from what i have seen.
In other words if its clean it will keep it clean but if its dirty it doesn't seem to have much more cleaning ability than any other oil. Not a slam its not a bad oil just an observation.
In addition to its cleaning ability PU has very low NOAK which in a high heat environment like turbo applications will create less varnish and deposits.

 

[Kamen]

Originally Posted By: Trav

You could remove the intake side plumbing and check for axial play (there should be none that can be felt), there may be slight radial play which is normal.


I actually thought of that and asked about it on the LGT forum but was told that 1) getting to the intake side is very difficult on an EJ254 engine (I had an idea about that from my EJ205) and 2) any disassembly of the intake pipe leads to leaks as it is very weak, and was generally discouraged from taking that route.

Originally Posted By: Trav

See if there no oil present. If you are not having any noticeable issues there isn't much point in going this far though IMO.


I saw no oil leaks anywhere, looking form above and underneath. No suspicious noises, no driveability issues, or any indication of any problem.

So, Pennzoil Ultra 5W30 (Subaru spec) or 0W40 (for cleaning abilities)?

Kamen

 

[skyship]

Originally Posted By: Clevy
Originally Posted By: tig1
Since you have no evidence of turbo problems I would not use a flush. You ask is PP is better tham M1? I can't speak for Penz but M1 was the oil Honda chose to lube their turbos with the HTO-06 high temp low deposite spec. I would use M1 5-30 which has that spec. For sure all M1 oils keep engines very clean and am sure it will be fine for your turbo as well. I would have to respectively disagree with Clevy about the base stock of Penz being better than M1, but no doubt PP or PU is a fine product.


I'm not arguing as I have no actual data however from what I've learned here pennzoil ultra uses a higher margin of group 4 basestocks that regular M1,the EP line and afe line do have a higher percentage of group 4 however I don't really think there would be much of a perceptible performance difference on a short drain interval like 5000 miles. Tig has hundreds of thousands of miles using M1 under his belt and that kind of experience is tough to argue against,so I'm not going to disagree with his point as he has experience using the exact same product,whereas I rarely run the same oil for consecutive runs.


It won't make any real difference which major brand fully synthetic (Inc HC) you use in terms of engine wear unless you have a top of the range Porsch that fries even an HC synthetic and cremates anything dino based.
Castrol, Mobil, Shell and Liqui Moly all make top quality HC and real German standard Synthoils. The oil filter and air filter are of more interest as some of the top of the range long life or high efficiency filters are sometimes better than OEM spec in the US, although I doubt that is true in the case of Subaru.
The major brand HC synthetics are fast catching up with the real McCoy full synthetics and I was even stunned to read my own beloved Synthoil High Tech was listed as a normal rather than a long life oil by LM themselves for a 30K km OCI car, so I will give up paying the extra next oil change.