Knocking noise on tickover

[Tony2179]

Hi i have a 2003 996 3.6 which has a knocking noise which dissappers when it reaches 1200 rpm i thought this was an idle tappit but some body has said it may be piston slap it throws out no smoke and is quiet when warm any ideas any body ? by the way it has just been serviced and has done 65000 miles

[mollytherocker]

Tony2179 said:

Hi i have a 2003 996 3.6 which has a knocking noise which dissappers when it reaches 1200 rpm i thought this was an idle tappit but some body has said it may be piston slap it throws out no smoke and is quiet when warm any ideas any body ? by the way it has just been serviced and has done 65000 miles

Did it start after the service?

[Trev450]

The noise you describe certainly sounds similar to piston slap. I would get a boroscope into the bores if I was you to look for signs of bore scoring.

[Tony2179]

no it was there before the service but quietened down after it i have heard 1 or 2 other 996's with the same noise. i know its not terminal as the car performs as it should is it a case of just live with it?

[Rockster]

Tony2179 said:

Hi i have a 2003 996 3.6 which has a knocking noise which dissappers when it reaches 1200 rpm i thought this was an idle tappit but some body has said it may be piston slap it throws out no smoke and is quiet when warm any ideas any body ? by the way it has just been serviced and has done 65000 miles

Could be piston slap. Or a bit of main/rod bearing or even crankshaft button (bearing) noise. Or chain slap from a slow to pressurize chain tensioner. The list is nearly endless.

Or it could be just normal. These engines are noisy enough when the weather is warm but in colder weather they can make a lot of noise.

If the noise quieted down after an oil change the noise is probably internal to the engine and valve or piston or bearing related.

Might be interesting to know what the hot idle oil pressure is. But since the noise is gone when the engine is warmed up...probably not worth the time/cost.

Absent any other signs of trouble or the noise getting worse I'd just live with it. My 02 Boxster makes a similar noise upon cold start and baby it has been cold lately (below 32F which is cold for here) and I go ho hum and let the engine idle a moment or two which I always do and the noise is gone and the engine is fine. Oh with 263K miles on it now.

If the noise bothers you, while I'm not a big fan of oil additives you might consider trying a bottle or two -- whatever it takes to treat 9 quarts of 996 engine oil -- of Swepco 502 oil additive -- the kind with "Micronized Moly". Various Porsche techs I talk with around my travels tell me they advise owners who use their car infrequently to use this additive to cut down on engine noise at start up if the owner simply can't or won't use the car more often.

[hartech]

Often if you listen to the noise while looking at the second hand of a watch - and count it - you can count over say 10 seconds - how many ticks there are. If there are say 60 to 70 ticks over 10 seconds - it is probably related to tappets - so no need for a boroscope check - but if it is more like 130 to 140 - get the check done as it will probably be bore scoring and the engine will slowly deteriorate until it is obvious and needs a rebuild.

Baz

[marky911]

Bloomin' eck Baz, you must be a fast counter!

130 ticks per 10 seconds is 13 per second. I can't count to 13 in a second.

Not taking the piss by the way. I'm interested in 996 Carreras at the minute, as my mate is looking for a MK1 aerokitted car and we don't want to buy a pup.

[Tony2179]

Thanks for all the input the oil pressure is at 2.5 bar when warm and on idle and about 4.5 to 4.75 bar when driving so i have no big concerns i will try the additive it won't do any harm. Baz it is less than 60 in 10 seconds Thanks Guys

[JonMac1985]

Hi, unfortunately I had this noise too on my 55 cayman s, bought it and drove the 150 miles home and then the knocking started. Turned out it was piston slap :-(....5k to fix and that was my first experience of a porsche lol. Hope its nothing as serious as mine.