c1arksta

hi all

on the last couple of days on a cold start ive had a slight knock from the engine it sounds like the start of piston slap but once the engine has warmed it goes and the car is fine for the day
it had a full service around 3k miles ago and the oil is like hunny in colour

just like to get a few thought to this and could it be the start of the end???

Marx Mcrae

iTrader: (4)

If the knocking goes when the engine is warm then it is piston slap

c1arksta

well when i got the car it never done this then out of the blue it started
ive not raced it about or treated it bad for something like this to happen

the car is a 1998 wagon uk spec with 154k on the clock but full history with subaru
this car has been loved and looked after

labpedro

Could be a few things....my knocking turned out to be a knackered Cam belt tensioner...when cold the piston wouldnt tension, and when iy got hot, it released a bit and the knock went away. was the belt slapping against the case, and luckily I found it before it went bang. easy to spot, just remove the cover on the passenger side, and start the engine....you will see the belt flapping if its that. I always thought piston slap was around the 20-30k mark on an engine, not at 150k?

TonyBurns

iTrader: (3)

MY97/98 cars are reknown for piston slap, uk or jdm, so its common(ish)

Tony

DeanF

iTrader: (1)

As Above extremely common on 97/98 & can just start out of the blue..

Dean

M444GY

iTrader: (72)

its most definately piston slap mate . mine is the same. my old one to

Dil660

mine does it in the morn 2 just leave it ticking for 5 then its ok

Smurf786

iTrader: (5)

What viscosity was the oil u used on service?

c1arksta

well not sure about the oil on the last service as i never done it
ive not had the car that long
so if it is piston slap what do you think i should do as i don't have a lot of dollar so rebuild is way out the window

scooby546

iTrader: (1)

If it is piston slap (and it sounds like it is) then I wouldn't worry about it - its not something that can be 'fixed' per say, and shouldn't do any harm. My understanding of piston slap is that it is caused by the forged pistons being ever so slightly smaller when stone cold, then when they warm up and expand a bit it they are the 'correct' size again. Mine does it, as did my last one, which was a UK spec Turbo 2000 similar to yours I think with 130K on it and it never missed a beat. You get used to it after a while. It is always worrying when your car starts making new noises tho

JohnD

iTrader: (5)

The oil grade will have virtually no effect on piston slap.
Piston slap has been around since the birth of the internal combustion engine. Manufacturers have devised ways of reducing it, but it can be evident even on new engines, just listen to a BMW M5 V10 start from cold! Ford even made mention of it in the Sierra handbook when refering to the earlier Cosworths. I had a Nissan Sunny back in the 80's that did it right from brand new!
It's a relatively common thing on the late phase one engines, as you have got. Drive gently, off boost, until the engine has warmed through. Unfortunately, with the colder weather coming, it will become more noticable.
At 154k I'm amazed it has only just become evident! (or was it already there but you bought the car during warmer weather, so it wasn't noticable?)

JohnD

c1arksta

yer when i bought the car the guy i got it from picked me up in it so it was running and hot so yer it could be that its always been there
ive taken to warming the car for ten min before i use it now and this seems to be working just fine
the knock is not hard but you do notice it though just giving it a slight small rev
like you say the cold weather is now on the way so i guess i will notice it more i just hope it does not lead to a bigger problem

JohnD

iTrader: (5)

You've got a fairly typical '98 car!
If the noise is still there after the temp gauge has reached normal, then it's time to consider possible action.

JohnD

c1arksta

when the car has reached normal running temperature there is no noise from the engine
infact this knock noise is the only noise to come from it other than that its a brilliant engine

oilman

iTrader: (9)

The knocking can be oil circulation at cold. What viscosity are you using?

Cheers
Guy

c1arksta

im not sure what it is as i never done the oil the change

im thinking of changing the oil to something thicker maybe this will help

your views please and if so what should i go for?

DeanF

iTrader: (1)

I changed my my98 wagon to a thicker oil 15/60 & it made the piston slap worse & more audible when cold, Eventually a swapped it for a mix of 3 parts Mobil1 0/40 & 1 part 5/40 fully synthetic & the slap was much less noticeable & dissapeared much faster....

Others though have had results using thicker, The thicker in winter will stay thicker for longer & may add to engine wear ! But at 150k miles it has already done very well

Dean

oilman

iTrader: (9)

I would use a 5w-40 and go for circulation especially as we are moving to winter. Better flow should help to quieten things down.

5w-40, 5w-40 oil, 5w40, 5w/40

Cheers
Guy

TimH

iTrader: (11)

Don't just let it idle for 10 mins - not good for the engine. Much better to start driving it immediately - off boost of course - and let it warm up that way. If you idle it, it take slonger to warm up and you are running it for longer when cold.

TimH

iTrader: (11)

Don't just let it idle for 10 mins - not good for the engine. Much better to start driving it immediately - off boost of course - and let it warm up that way. If you idle it, it takes longer to warm up, so you are running it for longer when cold.

c1arksta

would that not put more strain on the pistons if i run it knocking?

TimH

iTrader: (11)

My understanding is that the piston slap - assuming that's what it is - is harmless. The quicker you warm the engine (as long as you don't stress it) the sooner the slap goes away. IMHO of course

oilman

iTrader: (9)

The quicker the oil gets around the better for all the internals

Cheers
Guy

dj219957

yup you do more harm than good leaving a car stationary to warm up. better to drive straight off and keep off boost for a few miles.
you can try all the different types of oil in the world but none of them will 'fix' pistonslap with it. some may mask it slightly.