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 its rate/frequency would also increase accordingly but not get louder and later would get subdued or may be just overpowered by engine roar but not increased exponentially, so I figured it was not valves (hopefully).

What could it be then - 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 hard on a street for several times revving it to max on 2nd gear and heating it up almost to 250 and listened to engine - this knocking 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 is it even relevant?

Macster

My first guess would be the engine oil is getting aerated from track running and the knocking is the zero-lash valve lifters clattering cause of air in the oil. As the engine idles and air is removed from the oil and the aerated oil in the zero last adjusters is gradually replaced with unaerated the noise subsides.

Mobil 1 0w-40 might be a bit "light" for your usage and the engine. Some engines have pretty tight clearances and their oil budget is lower than an otherwise identical engine with a clearances a bit on the looser side. The engine doesn't have to be worn out either. The looser clearances can be explained by normal manufacturing tolerances that will see one engine leave the line with slightly optimum clearances and the next leave the line with less optimum but still within spec clearances.

Even if the engine's got normal oil requirements if the oil's got some miles on it and has gained some load of water and unburned gas this works to dilute the oil, to dilute or diminsh the anti-foam additive package and the oil's more prone to aeration.

If the oil's fresh for the track then possibly running a "heavier" oil, 5w-50 might be called for. You might consider switching from Mobil 1 to another brand of oil too.

A deeper oil pan with proper baffling could help, couldn't hurt anyhow. And the engine's existing oil baffling might be compromised. The baffling is some form of soft rubber like material and this material has been known to age and crumble. When it does it of course is no longer able to keep the oil around the pickup and no longer able to keep the more aerated oil from the pickup.

That you can't reproduce the symptom on the street is no surprise. It takes hot oil, and high/sustained rpms and extreme g-forces from a combination of accleration, cornering and braking for the hot oil to foam and the engine's oil sump to get a good portion of aerated oil and then the g-forces to move the better oil away from the pick up and to allow the more aerated oil to get within the range of the oil pickup.

Sincerely,

Macster.

utkinpol

5w50 mobil 1 does not seem to be available nowhere... what other oil brand would you recommend?
also - would it be possible/advisable to mix 0w40 with heavier oil like mobil 1 15w50? I just got oil changed before winter to 0w40 again.

Macster

I bought Mobil 1 5w-50 from an online source:

www.avlube.com

then seach for Mobil 1 5w-50.

Mail ordering oil is a bit of an inconvenience to me. I'm a buy the oil at a local supplier type of guy, cause I tend to procrastinate and then I don't want to wait for the oil to arrive and I don't want to pay extra to expedite the oil.

However, I found Castrol fully synthetic oil, 5w-50, for sale at local auto parts store (Kragen's) for $4.49/quart, about $2 cheaper than a comparable Mobil 1 oil.

I picked up 10 quarts and will use this next oil change for the Turbo.

You could mix 0w-40 and 15w-50 I guess -- some have posted doing this -- but ever since I had a motorcycle with 2-cycle engine I hate "mixing" oils so I try to buy an oil that requires no special blending or additive package to do its job.

If your car's a higher mileage example, like my 02 Boxster with 226K miles, you might consider using Mobil 1 10w-40 "high mileage" oil. I use it in my Boxster. But I don't track it.

Sure, the 10w-40 and 0w-40 oils have the same 40 viscosity but the 10w-40 oil has better HTHS numbers and appears to break down or degrade at a slower rate than Mobil 1 0w-40 oil based on some oil analysis results I've come across.

Sincerely,

Macster.

utkinpol

Thanks for very detailed answer, I will probably drain a bit of my 0w40 and add 2 quarts of 15w50 and will keep adding it at run sessions as oil will be burning out.

nosubt2

I too had the same noise after back to back to back to back runs in a autox at a high rpm. It sounded like an hydraulic lifter had run dry. I have not had it since, either on the track or autox.
I did replace the sump with the x51 sump after this incident

JFA65

Mobil One 5-50 can be difficult to find. I called the local distributor and they ordered 3 cases for me at retail cost then delivered to my business via their delivery truck. Ask your local Porsche dealer for the # of your local distributor.

Macster

That's kind of shade tree-ish... I assume when you take the car to the track the oil's fresh? Some owners track with 0w-40 oil and report no problems, but they always have fresh oil for track sessions.

Others run 15w-50 oil and everything in between.

If the oil's fresh, then I think you're going to have use a heavier oil or an oil that is better than Mobil 1 0w-40 oil.

If the oil's not fresh, at least treat the engine to an oil/filter change. You can use Mobil 1 0w-40 oil and see if the symptom reappears, but frankly this is like checking a gun to see it if loaded by aiming it at your head and pulling the trigger.

The symptom may appear and be benign, or the engine could spill its guts all over the track.

Best to fill the engine with a suitable oil for the use you will subject the car to right from the get go.

Ask the track junkies what they run/use/recommend.

Sincerely,

Macster.

utkinpol

Thanks again, oil was fresh, so, I guess I will need to experiment. I ordered 2 cases of 5w-50, 15w-50 is available everywhere, so, will see what will work best.

Macster

5w-50 a good choice to experiement with. A much better oil with of course a bit more viscosity and better HTHS numbers than 0w-40 oil.

Best of luck. I hope 5w-50 oil it proves to be the answer. Post the results if you don't mind.

Probably should add that a deeper oil sump -- as long as ground clearance isn't an issue -- might be called for even if the 5w-50 oil proves to cure the "ticking". Not only does a deeper sump increase the engine's oil capacity it gets the oil pickup "deeper" into the oil and further away from the aerated oil being returned to the oil sump through the de-foaming "pots". The deeper sump might have better baffling too which can only help.

Sincerely,

Macster.

RollingArt

HELLO ???

Did you guys see the response above ???

I would believe this to be the answer to the problem, not playing around with oil viscosities.

The oil is being aerated in the oil pump when it gulps air in the sump. Try any viscosity you like, it wont stop that from happening.

Get the x51 sump on the car before you smoke your motor.


Phil

utkinpol

I understand X51 sump that suncoast sells fits 996 car and for 997 it has to be machined to fit. Not sure if it is a DIY job.
-- Well, suncoastporsche had it in sale for $200, it is not such a capital expense, so, ordered it as well. Will see how it will go.

Can anybody comment on what specific trimming is required there to make it fit?

utkinpol

Is there any single person here who successfully installed X51 996 oil pan into 997 engine?

Will trimming instructions for Boxster fit 997 3.6L engine?

1999Porsche911

Fill the crankcase with Mobil 15W50. Foaming will be reduced. Much of the foaming in oil is caused by the breakdown of shear resistance (absolute viscosity) and Mobil 0W40 has little to begin with. Lifters depend on absolute viscosity and NOT marketting viscosity when engine is running.

utkinpol

Oil change is an easiest thing to do. I wonder still if X51 oil pan is the best answer for 997 engines or not.