Hi

I was hoping for some advice on the difference between piston slap and bearing noises. I have an MY00 UK turbo, engine is totally standard. It was due to go in today to have a jumping out of 5th gear problem looked at so it had not been started for nearly a week. It started first time like normal but when I got out to close garage I heard a new noise.

I have been trying to read up on piston slap noise and bottom end type knocks to see the difference. The noise was almost like hitting a bit wood with a mallet or something, like a thunk thunk knocking. It was not higher pitched or tappety, quite low. I listened for a minute or two then switched off as it also had a flat, probably ran for 4 or 5 mins in total. Noise disappeared after it was warm. I seem to get a bit of white smoke for the first couple of minutes running but this has always cleared, the noise is new though.

I'm dreading it being something that needs a rebuild as I just got the car a few weeks ago and have already had to spend a bit. Maybe serves me right for getting a cheaper higher mileage car? Its my first Impreza so I dont really have anything or any experience to compare it with.

Thanks.

 

white smoke is just condensation burning off mate nothing to worry about. my advice is check the oil level. when was last oil change?
sounds like piston slap to as it disappears once engine has warmed up. subarus are known for it. i have it on mine.
as i cant hear it im not 100% but it sounds like what you have. piston slap isnt a problem just let her warm up first before driving

 

Bearing noise would normally continue beyond the cold phase.
JohnD

 

i would say its piston slap too, its very common, mine does it when cold for the first min or so then goes away on idle, u can hear it a bit when starting off in 1st around 1500 revs then after say 10 min driving its gone once the pistons heat up and expand.....i had a compression check done to see if there was any probs and it came back 164lb pressure in all four cylinders so its a healthy engine

i wouldnt worry mate, i just let mine sit for 5-10 min idling before i drive, and always take it easy for the first 10 min or so before giving it boost

Burt

 

Sounds like piston slap to me.

Also, the "jumping out of 5th gear" is a common fault and if caught in time just needs a nut tightened in the gearbox. Can be done with the gear box in the car. So don't let anyone tell you they need to take it out and charge you a fortune.

 

Thanks for the info.

The car went in yesterday for the gear problem and I told them about the possible loose nut in the gearbox as I had read it in a few places. They were happy to do the work with the box still in the car and have confirmed it was the nut and it was in fact totally off. Hopefully the gears will all be fine now.

I'll have to listen out over the next few cold starts and see how the noise goes.

 

Water pump bearing and cambelt tensioner can make knocking noises that disappear when warm. Best get it to a mechanic with a trained ear to listen and hopefully diagnose.

 

It had the big service just 2 weeks ago and got cambelt and new tensioner so hopefully that should be okay. Would there be any other way of telling if it was the water pump?

 

mmmm was this noise there before the service? if not it might be worth taking it back.
great info on the nut james neill

 

i am having the same noise as yourself at the mo, it will make it until the engine warms up then once its warm it is still there but at a much less volume, the car still pulls really well though but am going to upgrade my engine and transmission anyway so this is only an excuse to use to do it anyway.

 

Not really, if its on the way out it will be working fine, but knocking. Problem is if the bearing fails it throws the cambelt, so its worth checking it out. A good mechanic can tell using a large screwdriver as a stephoscope.

 

The pistons expand very slightly when they are hot, so when they are cold they may rattle around a little making this noise.
It usually happens when its very cold, thats why when the cars warm the noise goes.