How serious is piston noise?

[pmm]

I understand that 'piston slap' is a much discussed topic, but I'm
afraid I'm confused about it, still, and I hope someone is willing to
help me out. I bought a 2003 Legacy with 72000 miles last Febuary - it
is my first car. In August (with about 76000 miles at the time) a
friend pointed out to me that the engine was making a tapping noise and
suggested that I have it checked out. The noise is loudest when I start
up and diminishes somewhat (so it seems to me) after the car runs for a
time, but it never goes away completely. I drove from Michigan to New
York with the noise, but with no other problem. The first mechanic I
took it to listened for a minute or two and said the pistons are ruined
and that I should replace the engine. He said that the car was probably
poorly maintained by the first owner and that the engine could seize up
at any time, which might destroy my transmission. So, I took it to a
Subaru dealer for a second opinion. The mechanic there, too,
recommended that I replace the short block (with a remanufactured one),
but when I asked whether poor maintenance caused the problem and if,
therefore, I should expect problems with other systems in the car, the
mechanic told me that the problem was a defect in the piston design,
that Subaru had a 'campaign' about the problem and would have replaced
the pistons for free if my car had less mileage. When I asked what
would happen if I didn't replace the pistons or the short block, he
said the noise would get worse. When I asked if the problem was more
serious and if the engine might seize, he began muttering about noise
and problems and having to replace something, etc. I couldn't get more
out of him, except that Subaru's are great cars and mine was worth
repairing. His responses made me think the noise was a matter of piston
slap.

The problem is, of course, the car isn't covered by any warranty and
the expense of replacing the short block is all mine. Is there any way
of determining whether or not the problem is 'piston slap' caused by
the design of the pistons or if the problem is that the pistons are
seriously damaged? (I've read some people report that they heard piston
slap in their cars even after the car warmed up.) What is the consensus
now, is piston slap something that could harm the engine, does it need
to be fixed? Is it worth replacing the short block if the car is no
longer under warranty?

Thanks for any advice you can offer.

 

[Carl 1 Lucky Texan]

I understand that 'piston slap' is a much discussed topic, but I'm
afraid I'm confused about it, still, and I hope someone is willing to
help me out. I bought a 2003 Legacy with 72000 miles last Febuary - it
is my first car. In August (with about 76000 miles at the time) a
friend pointed out to me that the engine was making a tapping noise and
suggested that I have it checked out. The noise is loudest when I start
up and diminishes somewhat (so it seems to me) after the car runs for a
time, but it never goes away completely. I drove from Michigan to New
York with the noise, but with no other problem. The first mechanic I
took it to listened for a minute or two and said the pistons are ruined
and that I should replace the engine. He said that the car was probably
poorly maintained by the first owner and that the engine could seize up
at any time, which might destroy my transmission. So, I took it to a
Subaru dealer for a second opinion. The mechanic there, too,
recommended that I replace the short block (with a remanufactured one),
but when I asked whether poor maintenance caused the problem and if,
therefore, I should expect problems with other systems in the car, the
mechanic told me that the problem was a defect in the piston design,
that Subaru had a 'campaign' about the problem and would have replaced
the pistons for free if my car had less mileage. When I asked what
would happen if I didn't replace the pistons or the short block, he
said the noise would get worse. When I asked if the problem was more
serious and if the engine might seize, he began muttering about noise
and problems and having to replace something, etc. I couldn't get more
out of him, except that Subaru's are great cars and mine was worth
repairing. His responses made me think the noise was a matter of piston
slap.

The problem is, of course, the car isn't covered by any warranty and
the expense of replacing the short block is all mine. Is there any way
of determining whether or not the problem is 'piston slap' caused by
the design of the pistons or if the problem is that the pistons are
seriously damaged? (I've read some people report that they heard piston
slap in their cars even after the car warmed up.) What is the consensus
now, is piston slap something that could harm the engine, does it need
to be fixed? Is it worth replacing the short block if the car is no
longer under warranty?

Thanks for any advice you can offer.

If it is piston slap, alternative oils may help quieten the noise. Also,
someone ( a GOOD preferably soob-experiemced mechanic) should confirm it
is not a TB tensioner.

There's extensive info on this at www.ultimatesubaru.net and likely at
www.nasioc.com as well. You could try searching the issues there for
info on oil and longevity (I think folks have gone 100s of thousands of
miles with the noise.)

Carl

 

[cobs]

I understand that 'piston slap' is a much discussed topic, but I'm
afraid I'm confused about it, still, and I hope someone is willing to
help me out. I bought a 2003 Legacy with 72000 miles last Febuary - it
is my first car. In August (with about 76000 miles at the time) a
friend pointed out to me that the engine was making a tapping noise and
suggested that I have it checked out. The noise is loudest when I start
up and diminishes somewhat (so it seems to me) after the car runs for a

[...]

We had what I thought was a piston slap sound on a JDM 2k rsk b4 - had
the timing belt changed at 98km which included a new tensioner kit, and
the sound has mostly disappeared.

...I say mostly as I'm still faintly paranoid about cold-start noises,
but I'm reliably informed it's me rather than the car

/C

 

[pmm]

Thanks for responding. Of course, finding a reliable mechanic is at the
heart of the problem. The two I've been to so far are pushing hard for
me to replace the short block, whatever the cause of the noise.

Your comment about oil reminded me: the first week in July I had the
oil changed, the guy who did it told me that whoever had changed the
oil previously had used the wrong oil. He put in 5W30 - as recommended
on the oil cap - he had drained out something thicker. Then in August,
I begin to hear the noise. If I tried thicker oil, say 10W30, and the
sound went away, would that mean that the issue was only piston slap
or could thicker oil simply mask a more serious problem with the
pistons?

 

[Jim Stewart]

Thanks for responding. Of course, finding a reliable mechanic is at the
heart of the problem. The two I've been to so far are pushing hard for
me to replace the short block, whatever the cause of the noise.

Your comment about oil reminded me: the first week in July I had the
oil changed, the guy who did it told me that whoever had changed the
oil previously had used the wrong oil. He put in 5W30 - as recommended
on the oil cap - he had drained out something thicker. Then in August,
I begin to hear the noise. If I tried thicker oil, say 10W30, and the
sound went away, would that mean that the issue was only piston slap
or could thicker oil simply mask a more serious problem with the
pistons?

I've stayed out of this thread because I think that
Carl and Edward are generably more knowledgeable
that I.

But since you brought up oil, I have to add my 2 cents.
Drain the 5W30 and put in Mobil1 10W30 and see what
happens. Use a genuine Subaru oil filter. Learn
how to change your own oil and filter so you know
what's going in and on your car.

I have a '99 Outback and a '04 WRX. They both run
noticably quieter on 10W30 than on the 'recommended'
5W30. I'm pretty sure the issue is not piston slap,
but valve clatter.

 

[M.J.]

The noise is loudest when I start
up and diminishes somewhat (so it seems to me) after the car runs for a
time, but it never goes away completely.

Theoretically, a thicker oil helps reduce piston slap at start-up
as it drains off of cylinder walls/piston rings much slower, so
that next time you start the car there is more oil left on these
parts to act as a cushion.

You have to experiment a little bit.

I would not rush to replace short block without first trying different
weight oils.

Don;t be afraid to try something much thicker say 15w-40,
straight 30w, or even 20w-50, depending on your climate.
If you live in the deep South etc., straight 40w is OK. Subarus
can handle thicker oils quite well; and one with 70k miles on
it is not likely to get hurt in any way.

If it is indeed piston slap there is a chance it may go away
with thicker oil. You mentioned there was already some thick
oil in it when you bought it in February.

Was it noisy then?

Perhaps previous owner was using thicker oils to deal with piston
slap and as the seasons changed and weather got warmer, it now
needs something even thicker than in February.

M.J.

 

[M.J.]

Theoretically, a thicker oil helps reduce piston slap at start-up
as it drains off of cylinder walls/piston rings much slower, so
that next time you start the car there is more oil left on these
parts to act as a cushion.

You have to experiment a little bit.

I would not rush to replace short block without first trying different
weight oils.

Don;t be afraid to try something much thicker say 15w-40,
straight 30w, or even 20w-50, depending on your climate.
If you live in the deep South etc., straight 40w is OK. Subarus
can handle thicker oils quite well; and one with 70k miles on
it is not likely to get hurt in any way.

I would like to add that I have successfully used straight 50, and 60,
oils to control piston slap in extreme temperatures i.e. summer time
weather in Phoenix, Arizona, and Las Vegas, Nevada (well above
100 degree F daily high temps, with nightime lows in 70s, 80s).

This was not done on a Subaru though.

M.J.

 

[pmm]

Thanks to all for the advice. I will certainly change the oil if the
problem is piston slap; however, I'm still unsure how to determine if
that is all it is. I called Subaru who checked with the mechanic at the
dealership. He told them that he thought the sound was 'excessive',
because it did not go away as the car warmed, and so he recommended
replacing pistons or short block. What he told me, however, was that
the sound was do to a defect in how the pistons were designed. Subaru
customer service said that there is no way to determine what causes a
tapping noise short of dismantling the engine. I certainly would rather
change the oil than the short block, but it seems that I have no
choice. Wouldn't it be too great a risk not to, if there is serious
damage to the pistons?

 

[Carl 1 Lucky Texan]

Thanks to all for the advice. I will certainly change the oil if the
problem is piston slap; however, I'm still unsure how to determine if
that is all it is. I called Subaru who checked with the mechanic at the
dealership. He told them that he thought the sound was 'excessive',
because it did not go away as the car warmed, and so he recommended
replacing pistons or short block. What he told me, however, was that
the sound was do to a defect in how the pistons were designed. Subaru
customer service said that there is no way to determine what causes a
tapping noise short of dismantling the engine. I certainly would rather
change the oil than the short block, but it seems that I have no
choice. Wouldn't it be too great a risk not to, if there is serious
damage to the pistons?

If you post your general area (city) both here and at
www.ultimatesubaru.net maybe someone can direct you to another mechanic
for better or at least confirming diagnosis.
You just may have a more serious issue than 'typical' piston slap.

I dunno

Carl

 

[pmm]

I'll give it a try. It seems to be the case that the dealer's mechanics
are quick to suggest replacing the short block whenever they hear a
noise they can say is 'excessive' because Subaru is willing to cover
'excessive' noise under the warranty. It dosen't matter at all to the
mechanic what actually causes the noise or if there are any serious
problems with the engine, and it's perfectly fine for people with newer
cars still covered. It's less fine for those like me who purchase used
cars. I've noticed that most of those who have posted messages about
piston slap or engine noise seemed to have cars that were still under
warranty and the issue was whether Subaru will cover actual piston slap
- it seems in the past they did with a little pushing and that fixing
it under warranty is more regular now.

 

[Edward Hayes]

Subaru has a TSB out on engine noise. If I remember correctly: from a
cold start if any piston noise goes away after 5 minutes it is
considered OK. If the noise persists after 5 minutes then the warranty
kicks in and the pistons or cylinder block is replaced. Maybe someone
can get you the TSB number so you can read it yourself.