I have 2002 Subaru Legacy L Wagon with 146,000 miles. The engine always has made a chugging/knocking noise since I bought it used 5 years ago. Most recently 2 mechanics told me that the engine is knocking and will die imminently. It has always made noise at start and lower RPMs but goes away at highway speeds. I am best man in a wedding that is a 5 hour drive and I am trying to figure out if the noise is in fact rod knocking or the less problematic piston slap.  Here is a video of the sound at cold start: https://youtu.be/nTeys6k34ww

Thank you in advance--I want to be sure to make this wedding! Should I rent a car or can I drive this Subie? 

Edited August 12, 20196 yr by ludwiggramsci

Sounds like a timing belt tensioner to me.  If it goes away after it gets warm I would think it wasn't rod knock.

 

Edited August 12, 20196 yr by Mike104

Piston slap mostly diminishes with engine temp. Rod knocks get worse. 

Cut the oil filter and check for metal. 

Your video doesn't load. 

GD

Copy paste the link GD! Copy and paste!  

As Mike said, it could be the tensioner. Easy diagnosis is to remove the driver’s side cam cover and visually inspect the tensioner in action - sometimes you can see it bouncing up and down. Other times you need to use a stethoscope (carefully!) to diagnose. 

The use of a stethoscope will tell you where the noise is coming from - bottom end, tensioner area or the top end, possibly - I’ve never used this method for piston slap. 

I hope for you it’s a tensioner. Replace before driving as this can cause big issues for the healthy running of your engine if the belt is allowed to skip teeth. 

When’s your cam belt replacement due? Get a full kit from a quality source - Japanese parts are best!

Cheers 

Bennie

piston slap sounds awful on cold startup, but generally goes away once the engine is at full operating temp. Colder weather makes it sound worse.

My 2002 Forester has piston slap and 253,000+ miles on it.

Thanks for these responses. I have not replaced the timing belt and water pump as I should have at 105,000 or so miles. How can I figure out if it is now too late to do this? And, if it is still worth servicing, can I get a recommendation and which brand I should get? Looking at the Rockauto site, they have brands like Gates, Contitech, Aisin, Dayco. The repair shops here in NYC just buy the cheapest no name kits so I want to be sure to buy something of quality, if in fact I havent already ruined the engine. 

Find out if it’s the tensioner first. If it’s the tensioner there’s no damage to the engine.  

If it’s piston slap I guess you’ll have to live with it. 

Cheers 

Bennie

As mentioned, the local NYC mechanics are not very thorough--how can I tell if it is the tensioner or in fact the engine? If it is the tensioner, should I have all pulleys, tensioner and water pump replaced? 

And if it is the tensioner, is it ok to drive for about 90 mins? (Rental place is outside the city) or is this so dire that I should simply not drive until the repair is made. 

Re: how’s to tell if it’s the tensioner - read my first post in this thread  

As for driving with a tensioner like that, I’m not sure. We replaced ours as soon as we could and reduced the use of the vehicle where possible. Ours didn’t bounce like the ones you can find on YouTube. 

You can see the belt bouncing in this one: 

Here’s another good one. I didn’t know about the trick of applying pressure to the tensioner. You don’t need the harmonic balancer on to test this. 

I hope this helps. 

Cheers 

Bennie

That's not piston slap.

Piston slap is light and almost clickity clacky, and will go away after warmed up.

That sounds like a timing tensioner slapping, and an exhaust leak too.

Thanks--good to know it isn't rod knock and the car is worth investing in a bit more. I bought a timing belt kit with new water pump. Anything else I should be sure to have the mechanic look at? Where would the exhaust leak be? 

2 hours ago, ludwiggramsci said:

Thanks--good to know it isn't rod knock and the car is worth investing in a bit more. I bought a timing belt kit with new water pump. Anything else I should be sure to have the mechanic look at? Where would the exhaust leak be? 

I hope you invested in quality Japanese parts for that kit.. Gates is using Chinese crap these days - not a good buy.

as for the exhaust leak - hard to say where exactly without crawling under the car.. could be manifold gaskets, could be a hole somewhere in the piping

On 8/11/2019 at 10:36 PM, ludwiggramsci said:

...rod knocking or the less problematic piston slap...

It's both.

5 hours? So get AAA and you get a 200 mile tow free. Just start early and have a backup plan. Request extra time off.