I have a 2002 Subaru Outback 2.5, 109k miles. I was wondering if I should replace them with that many miles or is their a practical non equipment tests that I could perform myself to guage them?

 

Thank you...

 

Gary

they're only a few dollars, i'd replace them.

 

given that you might have headgasket work to do in the future you might want to hold off until then since they'll need to be removed/easier access for that anyway.

You may want to try to remove a couple of spark plug wires at the spark plugs. If they are original, I would not be surprised if you report back they are most difficult to remove. With time and heat the plug wires seem to shrink wrap themselves to the plugs. and cannot be removed without destroying them. If you plan to replace the plugs, you will almost surely need to replace the plug wires as well.

Or they will be covered in oil because your spark plug seals are toast too. I would do valve cover gaskets and seals, spark plug seals, spark plugs, fuel filter, timing belt, water pump, idlers, cam and crank seals....

 

In other words you are 4K overdue on the timing belt, likely working on a head gasket very soon.

You might even have an extremly hard time removing the spark plugs frorm the head. Every 60K is the factory schedule for spark plug replacement on the DOHC 2.5. And it's only 60K because changing the spark plugs on the DOHC 2.5 is such a PITA. When the SOHC 2.5 has released the spark replacment interval dropped to 30K. I'll wish you good luck, but I hope that you don't need it.