Strange rattling engine sound in a car I am considering to buy?

jsoderbe · 06-18-2011, 04:59 PM

Hi,

I went to have a look at a 996 today. It is a 2002 cabriolet, with 118 k miles on it. The price is very good, and the color combo and option list suits me.

The car had some cosmetical issues, but the thing that caught my attention was a strange rattling sound coming from underneath the engine. I could only hear it on idle, when raising the idle to 1500 rpm it was gone. It can't be a main bearing, since the frequency was to high, but it did sound mechanical. I checked the AC, but the sound remained when the compressor was shut off.

Also, it looked to leak oil, since the oil sump was very oily and dirty. The idle oil pressure was about 3,5 bar when cold, and dropped down to 1,5 bar when warm.

The car ran fine, there was nothing missing power-wise, revved great, shifted great and so on.

So, does anyone have an idea of what he sound can be? I am not that good at the 996 issues, but I thought most was adressed on the 2002 model year.

Please let me know!

Thanks,

Johan

Carfax was clean, and showed 6 services was performed.

Rrrockhound · Rrrockhound's Garage

996 and rattle are two words you don't want in the same sentence. Walk away. Google "996 IMS issues" if you haven't heard about it already. Not that I'm diagnosing the car. I'm not. But why take a chance on engine failure, unless this car is so cheap you can put an engine in it and still be ahead financially?

jsoderbe · 06-19-2011, 07:13 AM

Yes, you are probably right, but on the other hand itwould be a shame to say no to the car and then find out that the 2002 996 suffers from rattling exhaust brackets....

I know about the IMS, but I thought that was updated on the 2002? I will do some reading.

Thanks,

Johan

jsoderbe · 06-19-2011, 07:47 AM

So, now I have done the research I should have done before....

Oh yes, that is the IMS rattling I heard on the car. It did not sound as bad as the ones at youtube, but the frequency is right.

So, what I still have to learn is if it is fixable, or if the damage has already been done from all the bearing particles. And, how much does it cost to fix? It look like te car has the RMS leaking as well.

Can I move the car with that sound, or do I have to fix it right away?

Thanks, Johan

Rrrockhound · Rrrockhound's Garage

According to most, once you hear that sound, you have mere SECONDS to shut it down before disaster occurs. I wouldn't give this car any more of my time.

88carrera · 11:00 AM

If this car is really of interest to you, I would spend the money ($200-$300) to have a well-qualified 996 mechanic do a complete PPI on the car. Not all IMS failures occur within seconds. I just had a new clutch put into my 2003 C2 at 45K miles and while the transmission was dropped, had the IMS bearing (not leaking or making noise) replaced with the LN Engineering ceramic unit. The original was showing signs of binding, but was not seriously degraded. The work, done by an excellent independent shop, was just under $2K, including the clutch and all parts and labor. If the engine on the car you are looking at has not suffered catastrophic failure (and it does not appear to have or it would not be running), you could negotiate a price reduction to replace the rattling IMS before it fails.

I would not drive this car, but would fix it immediately if I were to buy it.

If properly treated, these 996s are a great buy and are wonderfully performing cars.

Just my $0.02 worth.

Good luck.

jsoderbe · 06-20-2011, 03:28 AM

Thanks,

so, how much should I pay? $15k?

What exactly make the engine rattle when the IMS fails? Is it the bearing itself, or is it something mechanical, like the valves clappering against the pistons?

Thanks,

Johan

88carrera · 06-20-2011, 07:39 AM

Johan,

Let's look at the "fix" first. The very talented owner of the shop that has done my serious Porsche work for the last dozen years insists that in most cases a failing IMS bearing actually can be detected prior to failure by the high-pitched "rumbling" noise that it makes at idle as the lubricant begins to leak out and the bearings start to deteriorate.

The really loud sounds that are made last only a brief time and sound like a saw blade cutting into metal. This is the sound made when the IMS bearing assembly completely self-destructs, allowing the intermediate shaft to wobble at the end and cause the timing chains to jump, cut into engine parts and cause piston-valve contact. If this happens, you have a $15-20K problem because the engine is essentially trash.

So, if the IMS bearing in the car that you are looking at is just beginning to fail but has not yet taken out the entire engine with its demise, how can you tell and what can you do?

First of all, I would not even start this car up. let alone drive it again, until you know what is wrong with it.

If you have a sample of the oil analyzed by a place like Blackstone Labs (no affiliation, but I have used them for years), you can find out if there are elevated levels of metals that should not be in the oil. Also, if you could get the seller to allow you to take out the oil filter, you can carefully cut it open and examine it for metallic and plastic debris that would indicate bearing failure.

What you should offer for the car is up to you, but if you do not perform due diligence, you may well have a $15-20K problem as soon as you drive away with the title. On the other hand, if the owner cooperates with you in the problem diagnosis, you could get a very repairable car at a discounted price.

Good luck, and please let us know how this works out.

Jim

jsoderbe · 06-20-2011, 06:17 PM

Thanks, great input. I don't expect that car to be sold anytime soon, so I went ahead and looked at a older one, a -99 convertible. It was within budget, nice color combo, but the front seats was worn and needed significant work. Still, the car felt good, no rattling, ran well. Only thing is that the oil pressure gauge was broken! I'm not sure what to expect from that, but it sure would have felt better tó be able to read the oil pressure....

Any thoughts?

Thanks,

Johan

88carrera · 06-20-2011, 08:47 PM

Compare the 3.4L Mark I with the 3.6L Mark II 996. Several advantages exist with the newer car (power, aerodynamics, structural rigidity, etc.).

If I were making the decision, I would fully check out the newer car and find out exactly what is wrong with it. I would negotiate a deal with the owner to do the diagnostics. If it is the IMS bearing that is failing and the engine is repairable and if a good shop that is authorized to install the LN Engineering IMS replacement bearing is nearby (you can check their website to download a list of authorized shops), I would contract with them to do the IMS bearing replacement if I could buy the car at a substantial discount. If the problem cannot be determined accurately or if the seller balks at your requests, I would run from the later car.

This is just how I would approach the decision and I am not telling you to follow this route.

Good luck.

jsoderbe · 06-23-2011, 06:06 AM

Hi,

so, now there is a 2000 996 Carrera Convertible parked in my driveway!

The 2002 was located at a dealership, that felt they aready marked down the car with consideration to the work needed. In all fairness it was priced ok at $17500, but I would have wanted it for 12-13 which clearly was not happening. I understand them, they cant loose more money, and they will find a buyer for it for 17,5k too.
¨
So the -99 mentioned above turned out to be a 2000 when checking the VIN#. It has 118 k on it, tiptronic, silver with black full leather interior, covering the dashboard as well. It's not a very nice car to be honest, has some dents, worn front seats, top is a non-op and the leather on the dash has shrunk. On the plus side the breaks look great, engine runs fine withtout any strange noice, tiptronic shifts great, and of course the price was veeery good.

This suits me fine, good mechanical condition but challenged cosmetically, with a to-do list I can work on while driving.

Thanks for all support, this turned out great! I'm sure I'll be posting more questions from now on.....

Regards,

Johan

Thanks,

Johan

eastbay · 06-23-2011, 12:49 PM

wrong side of the country, but here are the seats you need:
A set of Porsche 996, all leather, fully electronic, seats.

no affiliation ed.

Schwarzeritter · 07-05-2011, 06:52 PM

It's difficult from a forum point of view.
The IMS is a distinct sound kind of gurgling groaning sound.
I would be skeptical, and sometimes IMS's can be replaced and go bad again.
Basicly there is a rubber seal and inside these little ball bearings and when the seal and so on goes to hell and a hand-basket. Lot of metalic shards, chunks and so on. It's one of those
things you just really pay attention to on a 996 or even 997. Better yet folks here is a video!

YouTube - ‪Porsche IMS Bearing Failure Explained‬‏

If you go with a factory part, I would inspect it after each track day or 8-10,000 mile services.
Remember, it depends on if you are modifed what kind of enviorments you are driving in. Oil tepm and coolent temp are different.

If you go with an up grade, the failiure or service life is a hell of a lot longer. But still you inspect things. Good luck -