I had a customer last week who complained about the lack of power and a high-pitch whining noise in his 2008 Subaru Outback XT Turbo.
While accelerating up Highway 17, he said the car lost power and the check-engine light came on.
I took a test drive with the customer, and the whining noise was deafening even at 15 mph. When I took the wheel, I felt the power loss in conjunction with the loud noise, which sounded like it was coming from the transmission.
We quickly returned to the shop, where I started the diagnostic overview.
The first thing I did was check the oil. The oil level was fine, but I noticed that the oil was incredibly clean. The customer mentioned that he had his oil changed right after the Highway 17 incident, hoping that would fix the problem. The customer also explained how he had gone 1,000 miles or so over the factory oil-change interval. I then asked if the oil was low at the time of failure; he was unsure.
Then I grabbed our Subaru Select Monitor III to check the transmission. There were no codes in the transmission. Still unsure where the noise originated, I used an automotive stethoscope and discovered that the noise was coming from the turbo.
We then addressed the bank 1 oil line that feeds the turbo. The line runs from the valve actuator to under the turbo.
At each end of the oil line is a union screw – a hollow bolt with a screen in the middle of it. The union screw’s purpose is to keep oil impurities from reaching the valve actuator solenoid and turbo bearings.
If engine oil is burning off or the oil has been left in for too long, it will become saturated with carbon. The engine oil filter will try to capture as much as possible, but some carbon deposit will eventually become distributed throughout the engine. Carbon does not act like oil, and it likes to plug things up.
After we removed the union screw at the valve actuator, we found that the screen was missing. We then cleaned and tested the valve actuator. It was fine.
Next we removed the turbo and checked the lower union screw. The lower union screen was completely plugged. The oil had stopped flowing to the turbo.
Turbos spin at incredibly high RPMs and need good oil pressure at all times. The car figuratively had a heart attack from its arteries being clogged.
Unfortunately for the customer, the turbo had to be replaced.
Some newer cars have oil-change intervals as high as 12,000 miles, but not late-model Subaru turbos. The factory oil change is 3,750 miles on these cars.
Subaru has issued a recall on some of the turbo oil lines, yet this Outback had already had the work done.
So a word of advice to Outback XT owners: Check your oil level regularly and be sure to change the engine oil by or inside of the mileage interval.