Hi,
My uncle drives a 2010 Subaru Forester 2.5L and it's on it's 3rd engine. I guess first one seized, was replaced with a used one that didn't last long, and now this was another used engine with low miles and now years after owning it randomly my car started to lug and lose power when I pressed the gas. I had a local shop fix the issue, $2100 later. They said it was a stripped spark plug. Well now 30,000 miles later, all of a sudden, the same things happening. Nothing has been done to the car in that amount of time no one else has touched under the hood since the shop did last. Now they want $4700 to replace the valves cause the same spark plug is stripped again😱 so 1. What could be causing this issue? 2. How can I ensure that the next engine, if we decide to just swap the engine, won't have the same issues. Or what’s the best way, in your opinion, to fix the car?
Very desperate for advise, thanks a million-
Adam
Someone must have stripped the spark plug threads on that used engine. If the threads were "repaired" and have failed on the same plug then the shop botched the repair job.
About all I can think of that you could do when installing a used engine is to check the plugs and make sure they are not cross-threaded. If they are you'll wind up with the same problem. (Probably not a bad idea when putting in any used engine with aluminum heads.) What I do not understand is why the shop wants to replace the valves due to stripped spark plug threads. That's not making sense. Granted, to repair the threads you have to remove the cylinder head which in a Subaru means pulling the engine out so it's an expensive job, but certainly not $4700 worth.
The other issue with those engines is they are very prone to head gasket failure. It would not be a bad idea when installing a used Subaru engine of that vintage to replace the head gaskets as a preventative measure. Ditto for the timing belt. The time to do it is when the engine is already out of the vehicle.
It sounds to me though that it may be time to cut your losses and look for another car.
It's always a good idea to use an anti-seize compound on the threads for installation.
Good point, though some spark plug manufacturers like NGK say not to do that because the threads on their plugs are already treated not to damage aluminum. The other issue with aluminum heads is that the spark plugs really should be tightened up with a torque wrench but a lot of people don't do that. If you wail away on a plug in an aluminum head the way you would with cast iron chances are the threads will be damaged. (Aluminum heads have been common for so long though at this point any mechanic should know how to properly deal with them.)
https://ngksparkplugs.com/en/resources/5-things-you-should-know-about-spark-plugs
Right you are, Chuck. But because the plugs are steel and the head is aluminum, the corrosion caused by the dielectric reaction of the different metals makes it a prudent practice to use the anti-seize compound, although sparingly. Also, the use of a torque wrench is excellent when used with manufacturer's specs.