Knocking Noise on Tick Over

[Lee2246]

Hi Guys,

I recently bought a 2003 Porsche Boxster S, and it's started to make a knocking noise on tick over only when the car is warmed up.

Can't really make out exactly where it's coming from but the tiniest bit of throttle and the knocking stops straight away. Doesn't knock at any other part of the rev range and doesn't knock at all when cold or on start up.

Any one have any idea what this could be?

Thanks,
Lee

 

[irb26]

Exhaust shields?

They quite often rust and then knock about

 

[chrishak]

Ditto the above or perhaps a sticky hydraulic cam-follower?

 

[Temmplar]

I second a possible sticky hydraulic cam follower. Is the noise a light tapping which may not initially be there on start up but gradually appears over a few minutes?
I had this on my 3.2 S and as the tapping disappeared with an extra few hundred rpm a successful fix was to remap the Ecu to idle at 900 rather than 700 rpm?
Suggest you give that a try?

 

[Lee2246]

Hi, guys,

Thanks for the advice, had the car looked over yesterday and the mechanic thinks it's a sticking cam follower.

He said it is a possibility it's got the wrong oil in it, so going to try changing that first.

Temmplar - funnaly enough my mechanic suggested turning the rpm up a touch if it still does it after the service, so could be an idea. To swap the follower what sort of cost do you think I'm looking at?

Thanks again,
Lee

 

[Temmplar]

Try the oil first if it due a change or think it is the wrong specification. My money is still on the sticky cam tho, not economic to start fiddling with the head when an idle remap costs relatively little. To swap the follower is likely to cost more than a few hundred pounds, I’d budget say £300-400? depending where you go? The idle remap cost me £100!!

 

[Motorhead]

Lee,

The flat-6 can be a very "tappety-sounding" engine compared with in-line and V-engines which are better encased in the engine bay. With the engine being mounted low in the chassis, radiated sound from the engine gets reflected from the ground and out the sides of the car making things sound worse than they are.

As others have said, see if an oil change improves matters and give the car a long run to get everything properly warmed-up, using as much of the rev range as possible. However, I have to say that doesn't necessarily guarantee any improvement: sometimes my Gen2 CS is relatively quiet at idle but sounds like a bag of nails after a spirited 30 mile run..!

Jeff

 

[Lee2246]

Hi Guys,

Just to let you know had the car serviced and although it's made the tapping noise seem quieter when warmed up it's still there, so going to get the follower looked at / changed. Filter was clean though with no 'bits' in it so that's good []

Thanks again for your help and I'll let you all know how I get on (in case someone searches the same issue in the future).

Lee

 

[BrianJ]

How many miles has your car done Lee?

 

[Lee2246]

How many miles has your car done Lee?

Just under 92K

 

[BrianJ]

Ah. Unlikely to be the problem I had on my 2003 at about 15k, if I remember rightly. "A bad batch" of cam followers hadn't had the correct heat treatment and one of my camshafts knocked a hole in a follower (as it subsequently turned out) in the south of France on a summer bank holiday weekend. No help available so drove home slowly. That really did making a knocking noise. I heard of several other cars having a similar problem at a similar mileage (some several years later due to their low annual mileage) so very unlikely to be your problem.

 

[Lee2246]

Hi Guys,

Just to close this one out,

Had the car looked over by John at Unit 11 in Warrington (really nice guy). With the stethoscope he had a good listen an determined it was bank 2 making the 'tappet' sound, however as before touch the throttle a tiny bit and it goes and all sounded fine. When the rocker cover was removed everything looked fine, not obvious signs of wear or anything. Cams fine, tappets fine, chains fine, even put a scope down all the bores but all looked good. So John spoke to someone at another specialist and apparently this is becoming a common thing with Boxster of this age / mileage (92k) and doing a full top end rebuild doesn't cure it. Basically the long and short of it is it could just be the general wear and tear of the engine it drops out of spec on tick over when warmed up, so other than a full engine rebuild (as in new everything) its always going to do it. The advice is just to raise the rpm by 50 - 100 and this gives a touch more oil pressure on tick-over and stops the tapping sound.

John also said he always thought the oil pump was a bit small on the Boxster so could just be an inherent design flaw that only becomes apparent when the engine starts to rack up higher mileage? Either way, nice to know the engine isn't going to explode (touch wood) .

Thanks again for the help.
Lee

 

[Peter_Bull]

Perhaps a slightly thicker oil might help reduce the noise?

 

[CLIFFWILKINS]

Always found Castrol Magnetec made any of our older cars in the past very quiet
Never used it on a Porsche though.

 

[Lee2246]

It's got Mobil 5W40 in it at the moment, what would you suggest going up to?

 

[Peter_Bull]

It's got Mobil 5W40 in it at the moment, what would you suggest going up to?

To be honest I would ask our Register Director, Albert Walsh, who also works in the motor trade. But then again you really need to be a member to get the contact details.

Hopefully there will be someone who comes on here who has better knowledge than me to assist you.

Best of luck.

 

[Motorhead]

Lee,

I would think that Mobil 5W-40 should be fine (I assume that 0W-40 is recommended by Porsche for your car?).

A Mobil 1 High Mileage is available, which I think is 10W-40, but you may have difficulty finding it.

Personally I wouldn't worry too much about the knocking if it clears itself under normal driving conditions. After all the best thing to do is get in the car, start it up and, when the idle speed has stabilised at about 700revs/min, drive it away immediately. That way you'll avoid prolonging the idle phase.

Jeff