Just bought a 99' Outback Limited from police auction. It runs well, all fluids are normal, head gasket has been replaced same with the timing belt. But I've noticed that occasionally the engine makes a knocking noise and I have no idea what that means. Everything seems to run right but everyone in awhile it knocks and I'm not sure if I need to be concerned or not. I plan on taking it in, but I was hoping to get a better sense of what the issue could be.

 

It seems to knock only when I let off the gas, doesn't do it any other time.

Edited March 8, 201115 yr by aripurdy
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Gotta give us more info.. knocking when cold?? Warm? Does it sound like its coming from just one side of the engine?

 

the EJ25's are known for piston slap when cold but tapers off when warm

worst case , it's rod knock. that's pretty much terminal.

 

mid range case, it's piston slap. this usually happens when cold at start up and goes away, or mostly goes away, as the engine warms up. this is a pain but not an indicator of eminent failure. you can live with it, i did for 40k miles and then i sold the car.

 

but it could be the t-belt tensioner. they can make a knocking noise whnen the start to fail. and if it fails you will be looking at a head gasket / valve job. very expensive. i suggest you buy a $4 ''mechanics stethoscope'' from harbor freight and listen for the noise on the timing cover under the alternator. that is the general location of the tensioner.

 

if that's what is making the noise, replace it sooner than later, a failure is expensive.

 

if the noise is not '' rod knock'' i would do a complete timing belt job, belt, water pump, tensioner, and all idlers. and any leaking seals.

I agree with John. An intermittent knock falls into the idler bearing/tensioner category.

 

Would be helpful to know exactly when the noise occurs though. Cold? warm? During throttle change? Shifting, turning, braking?

How loud is it? Rod knock is almost deafening at 2000 rpm.

I usually notice the rod knock the most - and this is my test.

 

Let it warm up. Spirited drive, or 10 minutes at idle. Then grab the throttle linkage and rev it up a bit. When the engine is decellerating probably at about 2k is when I hear it the most. Try and put your head back towards the throttle body on both sides.

 

That's my test.

 

If it goes away when warm it's piston slap as already stated.

the timing tensioner can have slop in it as it's hydraulic and will "give" making a loud rapping noise under different loads. it can be mistaken for rod knock and more ominous issues. this is an interference engine though so if it is that, you want to get it looked into right away.

Yes, I would say timing belt tensioner is your first stop to check. If you remove the timing belt cover (fairly easy job), and run the engine, check if the belt is "jumping." Also try pushing down on the belt when the engine is not running, look at the tensioner and see if it's moving, if it is it's probably bad.

 

I believe most of the 99 Outbacks had the EJ25D, and since you said the headgaskets were done i'm assuming they probably went, which may have overheated the engine (since people tend to continue driving them). If this happened it's quite possible it's a rod.

 

If you're mechanically inclined, I would check the timing belt tensioner. If you can confirm (either yourself or by another mechanic) that it's NOT a rod, then like was said before do a complete timing belt job, and replace the idlers, tensioner, and water pump. If the gaskets were done and the rods aren't knocking, this would be a worthwhile investment.

 

Finally, if it is a rod, just let it blow up. When you need a new engine, swap an EJ22 in there which you can find pretty cheap, it will plug and play without issue, and it will go forever.

Another thing these motors are good for (besides #3 rod knock after they have been overheated) is valves that are not adjusted to spec. I don't mean to be a wongleflute, but I'd say 80% of Subaru owners cannot tell the difference between a valve tap and a knock.

Another thing these motors are good for (besides #3 rod knock after they have been overheated) is valves that are not adjusted to spec. I don't mean to be a wongleflute, but I'd say 80% of Subaru owners cannot tell the difference between a valve tap and a knock.

 

#3 happens to be where I usually can hear it the most. I'm usually standing at the front with my right had on the throttle and stick my head on the pass side back by the airbox on the throttle body. That's where I have the best success in hearing rod knock. I don't know if #3 wears first of there is more other noise on the drivers side. But that's exactly where I've learned to listen.

I would honestly just drive the car (mine lasted 75,000 with a bad knock). In the meantime, look into another engine and if reliability is important, think seriously about the EJ22 swap. A little less powerful, but will run forever.

 

It actually is a crap shoot. Mine had a knock for 5 minutes then went away. 1000 miles later all hell broke loose in a rather exciting way.