Metal knocking engine sound after run sessions

[utkinpol]

Hi,

Just curious to ask - several times during last season after quite intense auto-x runs (1.5 miles) engine had very pronounced metal knocking sound right after run which would slowly fade away, it would be knocking at same rate as exhaust sound while running on idle, if I would step on throttle it would also increase accordingly but get subdued and then overpowered by engine roar but not increased exponentially, so I figured it was not valves (hopefully).

What could it be than - an oil separator valve? But why? Is it typical? I run regular 0w40 mobil 1 oil, should I perhaps get 5w50 or 10w50 to remedy this? or should it be simply ignored?

I tried to run my car very heavy on a street for several times revving it to max and heating it up and listened to engine - sound never appeared so it seems to be related to hard cornering only most likely. Is it typical for 3.6L 997 C2 engines? Should I get something for this, don`t know, like 996 X51 modded to 997 oil pan? Or it is not relevant?

[flyingpenguin]

This sounds like the hydraulic valve lifters tapping due to oil starvation. I had this happen on my 2000 996 (3.4L) at our first Performance Driving School with LSR PCA back in October of 2008, doing righthanders on the wet skidpad. I replaced the oilpan with the X51 version and have not seen this happen again. At the same time I also switched to M1 15W50, so cannot say for sure which had the most effect remedying the issue.

In any case the two changes significantly reduced the drop in oil pressure during fast and prolonged righthanders at Texas World Speedway (eg. turn 2 / 1 going clockwise).

I would start with a thicker oil before modding the oilpan.

JP

Edited December 25, 2009 by flyingpenguin

[utkinpol]

This sounds like the hydraulic valve lifters tapping due to oil starvation. I had this happen on my 2000 996 (3.4L) at our first Performance Driving School with LSR PCA back in October of 2008, doing righthanders on the wet skidpad. I replaced the oilpan with the X51 version and have not seen this happen again. At the same time I also switched to M1 15W50, so cannot say for sure which had the most effect remedying the issue.

In any case the two changes significantly reduced the drop in oil pressure during fast and prolonged righthanders at Texas World Speedway (eg. turn 2 / 1 going clockwise).

I would start with a thicker oil before modding the oilpan.

JP

Is it 'safe' to mix M1 0w40 with M1 15w50 if I drain, say, a half gallon of current oil and add same amount of 15w50?

[flyingpenguin]

Assuming the two oils to be mixed meet standards, mixing oils initself is not "unsafe". I doubt whether adding 2 qts will do anything significant. Roughly speaking you would end up with a 3.5W 42. Not much of an improvement.

I would do a complete oil change.

If you are in the colder part of the US, I would recommend you use the 5W50 instead of the 15W50 for the winter months. I am in Texas and only drive the car when its not too cold (ie. over 50F).

JP

Edited December 27, 2009 by flyingpenguin

[Ahmet]

Sounds like lifters, it's common on all kinds of cars. My 996 with a reman'd motor did it as well...

[utkinpol]

Sounds like lifters, it's common on all kinds of cars. My 996 with a reman'd motor did it as well...

Is there any person here who have installed X51 996 oil pan into 997 3.6L engine successfully? What specific trimming did it require?

Edited December 28, 2009 by utkinpol