How serious is piston noise?

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.

Reply to
pmm
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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

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and likely at
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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

Reply to
Carl 1 Lucky Texan

[...]

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

Reply to
cobs

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?

Reply to
pmm

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.
Reply to
Jim Stewart

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.

Reply to
M.J.

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.

Reply to
M.J.

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?

Reply to
pmm

If you post your general area (city) both here and at

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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

Reply to
Carl 1 Lucky Texan

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.

Reply to
pmm

Reply to
Edward Hayes

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