possible severe engine damage - would appreciate diagnostic advice
 

Well, after 5 years of essentially trouble free operation, it looks like the car has its first major problem.

2001 S, 113 Kmi, 45 Kmi on new engine (replaced by PO).

Yesterday morning I tried to start the car. Garage temp was 47 deg F, and the car hadn't been started in five days.

Upon starting, there was immediate extremely loud clatter from the engine. I shut off the engine immediately. The clatter sounded pretty much terminal.

Some smoke wisps came from the exhaust, and there was a distinct burning smell. I verified that there was no fire and started it again. I figured, if it's already toast, another starting attempt wouldn't hurt much.

On the second start, the engine did not seem to want to catch. After 10 seconds it finally fired up. Loud clatter, not as bad sounding as before. Some smoke from the exhaust, but could have been moisture burning off. Idle was steady at 1100rpm (usual warm up).

Gave it some gas to around 1500rpm, clatter went away completely, car idled perfectly.

Drove the car out of the driveway, for one block. A lower-frequency clatter returned at > 2000 rpm, so I headed home and parked the car.

Summary:
Idles perfectly, seems to drive fine, but makes pretty awful clatter noise coming from the engine. No CEL. No other warning lights, all fluids seem fine. No leaks or obvious problems.

So... what could this be? Judging by the noises, I expect severe internal damage... but the fact that it idles and drives fine confuses me.

Any diagnostic advice?

I am planning on:
0. visual inspection of engine compartment and below
1. drain the oil through a cloth filter, inspect for debris
2. inspect spark plugs
3. refill with oil, do compression check

Any other suggestions? Thanks!

You are inviting trouble if you run it another rev.
 

Assuming there is some internal damage, it will only get worse. Any revs will only spread any debris throughout the oil passages and can lead to the need for an expensive engine rebuild or replacement.

I'd immediately read any codes for clues. Post the codes.

Pull the oil filter off (without starting the car) and examine the spread out filter element for any signs of debris. Post pictures if you find any and describe the color and composition of the debris.

Pull the serpentine belt and feel if there is any play on the water pump.

And, if you don't feel able to do those things, I'd arrange for the car to be flatbedded to the most knowledgeable mechanic specializing in the internals of the M96 engine that you can find. Without starting it.

My reasoning is that spending time and money diagnosing reduces the risk of having to spend even more.

Good luck...I'll hope for the best results for you.

Your plan looks good. Inspect the oil, coolant, spark plugs, and oil filter. If no grenade fragments:

1. Broken valve spring
2. Water pump sheared
3. What else??

Reading what you wrote and not having an audio clip, this is my $.02;

1. The smoke at start-up is normal.
2. The burning smell...stray cat?
3. Clatter sound, do you have a mechanic's stethoscope? Looks like a doctors but has a rod on the end. If you can get your hands on one...start the car, crawl underneath and start probing to isolate where the sound is coming from. I'm hoping its the water pump impeller coming apart (water temp never climbed above average?).
4. The fact that you drove it and it still idled fine doesn't sound like something terminal. You might want to pull the front access cover and check your pulleys and the water pump at the same time.

Good luck and please let us know what you find. If you find a mechanic is going to break if off in your backside with an outrageous cost, have him prove whats wrong first.

You may be catching the beginning of an IMS bearing failure. Many people who've had that happen describe the sound as a clattering, like if you filled a coffee can with heavy bolts and shook it violently. If this is what you're hearing, don't even think of starting that engine again.

If you can catch an IMS bearing failure early, the engine can be fixed. If the intermediate shaft breaks, the engine is almost always toast.

I would call the dealership that installed the "new" engine & see what they say but I would not mention restarting the car the 2nd time. What alarms me is the smell you spoke of. When the IMS bearing seals allow oil to pass thru the seal to the bearing it washes away the "permanant" grease & the oil stays in the IMS tube & since this oil stays in the IMS tube when it gets old it smells very strong. My guess is your engine has jumped cam timing & may be hitting pistons on valves since it did not want to start like it normally does. Thanks for your great summary of what happened & a speedy recovery. :(

Depends on your definition of "a lot of clatter" :-(

I would do the following: without turning the car on.
In no particular order:

check your oil level is it full (or at least not low)

check your coolant -- any intermix?

check codes with a duramatic -- even if no CEL.

pull the plugs and boroscope the cylinders, check compression

check the timing.

see if you can boroscope the chain tensioner paddle
and check to see the chains are in good order.

pull the oil filter and check for metal flakes.

pull the oil pan housing and look for metal and other debris.

sadly -- there is no way to inspect the IMS without really getting into things.

where are you in Texas -- I work with a mechanic in Austin
that rebuilds M96 engines.

Love to help you if we can. For a faster response -- send me an email,
I don't always see the PMs.

Mike
mike@lonestarrpm.com

Could be many reasons but from my experience, and knowing this is the "S" model engine, i'm putting my money on a broken valve spring.

Good luck with the diagnosis and report back if you can!

I'm all for more knowledge -- my questions are not questioning your opinion
just seeking more information:

What experiences have you had with broken valve springs?

What is the sound like on an M96 engine?

Why is the "S" a factor in your decision.

thanks,

mike

Thanks, everyone, for the helpful suggestions; I appreciate them!

My work schedule hasn't allowed me to do any further investigation, but I hope to be able to spend some time on this on the weekend. I will report back and update.

BTW, no trouble codes stored...

FWIW, broken valve spring was the first thing that came to my mind as well... but this needs further investigation...

Update:

I drained the oil and filtered it through a washcloth. No foreign particles. No intermix. Removed the filter and cut it open - nothing. Looks exactly like the previous three filters I cut open.

Re-filled with Rotella 5W40 (same as before; last oil change 5 months / 1 Kmi ago) and started it. Smooth idle, no noises.

I haven't checked for noises above-idle yet (all engine covers are off, and the motor gets quite loud when you go >1500 rpm).

I guess I'll look at the spark plugs tomorrow, just in case.

Is it possible for a valve spring to be broken, and you can't hear it at idle?

Were you low on oil?

You might have had a weak lifter or hearing chain noise

All hard to tell without knowing what it sounded like.

Mike

At idle I don"t think you'll hear it, idle should be normal being it's a four valve set up. Remember, if it is a broken spring, the chances of dropping that valve increase significantly with greater RPM because it will float a whole lot sooner. You might want to pull the valve covers and do a look see first.

I have seen a handful of broken valve springs including a few M96.

Common symptoms:
Top end clatter rising with RPM, one fouled cyl, no debri in oil pan, possible backfire. A reasonably easy fix if you catch it early.

Yeah sorry i forgot to elaborate - it's a friend of mine, who has a 2003 S model that exhibited the same symptoms. It's definitely weak having only one data point, but sometimes i just go with my gut feelings~

My mech/shop partner is deaf but is very skilled rebuilding M96 engines

I help out by being his ears, i have not had the chance to hear a broken valve spring before.

Mike

If I'm reading this correctly, the OP has now turned the motor over a 3rd time at least.

If you keep doing that, the sympathy quotient is going to rapidly drop to ZERO!

These are expensive motors. Until you have a competent, qualified person look it over, leave it be. For your own sake!

Good luck!

Cheers!

Another update.

Spark plugs looked okay, albeit a bit sooty for my taste. 19 Kmi / 3.5 years on the plugs. Perhaps I need to look into the O2 sensors...

Plug #1 was noticeably loose, perhaps barely hand tight. My hypothesis is that this plug was never installed tight enough and loosened due the recent extremely cold outdoor temperatures around here. This perhaps could explain the clattering.

Compression test yielded good consistent numbers (>140) across all cylinders.

I installed new spark plugs and started the car. Smooth idle. Slowly reving up to 2500 rpm, there were no noises.

I can't do a road test at this time, because I discovered that my rear axle boots are torn and need to be replaced. They were fine four months ago; perhaps also a victim of the cold temperatures.

For now, I am hopeful that this could be the happy ending to this story... we'll see.

Thank you, everyone, for your helpful advice and suggestions!

I agree that the first restart after the noise was reckless. No doubt about it. Subsequently, however, I think I took reasonable, calculated risks.

But it perhaps doesn't make much sense to discuss individual risk perceptions. I started this thread to ask for diagnostic advice. What would have been the diagnostic plan that a competent, qualified person would have followed?

The compression numbers certainly seem to be a good sign. Kind of rules out piston/valve contact. Did you figure out where the oil leak is coming from?