Subaru Repairs

There is the old adage “you can learn something every day”.  I have to admit that when it comes to tough or complex problems I’m bit of a mechanical geek.  On day two of the new year I was presented with one of these complex problems.   One of my long time Subaru clients brought in their 2009 Subaru Forester 2.5 L non turbo (87,000 mile).  The customer was complaining of a rattling sound from the engine. She stated she heard it most on startup but it usually did not go away.

This car happened to be about 3000 miles over due for its oil change so the first thing we did was check the oil.  We checked it and yep, it was low. Problem solved? After doing the oil change, however, we could still hear a faint rattling in the back ground.  It was so faint that I thought we may not even near to check further.  In most cases if oil goes too low it can cause damage to an engine. Once that damage is done it is hard to correct it. 

Even though there is a high probability that this will be a mechanical and not electrical problem the next step was to check engine codes. We then checked codes in engine control.  Codes can give us very important clues on which path to follow, yet there were no codes in this case. 

The next step was to check compression.  To check compression we have to remove the spark plugs. When removing the spark plug wires we found that oil had been leaking on the inside of the spark plug tube wells (spark plug tube seals). The spark plug tube seals are parts installed into the valve covers.  All boxer motors have problems with their valve cover gaskets and seals because the engines lay flat and not up right.  We removed the driver side spark plug and check compression.   Cylinder # 2 had 180 psi and Cylinder #4 had 175 psi.  Both of these number were acceptable.  The interesting thing was that the # 2 spark plug was almost all the way worn out and the # 4 spark plug only had normal wear.

Subaru does not have a valve adjustment as part of their normal service schedule.  Most cars today do not need valve adjustments as most engines have hydraulic valve adjusters, meaning the valves automatically adjust.  This particular 2.5 liter motor, however, had adjustable valves.  Since we knew that we had to replace the valve cover gaskets and spark plug tube seals, we felt strongly about performing a valve adjustment. We called the customer and got the ok for the work. 

What we found next was interesting. After removing the passenger side spark plugs #1 and # 3 we found the same thing.  The # 1 spark plug was almost gone and the # 3 spark plug had normal wear. During the valve adjustment we found that the # 1 cylinder and # 2 cylinder exhaust valves were loose and all other valves were tight. If a valve adjuster is loose the rocker will have a larger gap between the valve. A loose valve will not open all the way. That gap can cause a  ticking or rattling sound. If the valve adjuster is too tight it will open the valve too much. Tight valves can cause compression problems and carbon buildup that can burn valves.  

Why this was so interesting was the #1 and #2 cylinders that had loose valves completely wore out the spark plugs. We feel this happened because the loose exhuast ajduster was not letting all the heat out of the cylinder. The by product was extremely worn spark plugs.

After the repair the engine ran great and there was no more rattle. From here on out we will be monitoring our late model Subarus that have adjustable valves a little more closely after 80,000 miles.