My GL450 makes a heavy ticking noise at very low rpms, only at idle. 600 rpm it's there; raise speed to 800-1000 and it's gone.

It's hard to hear in the video; it's the tapping or heavy clicking noise in the background. From the engine bay it's drowned out by the other motor noise.

Too low pitched for a valve noise. I was wondering if the timing chain tensioner, being filled hydraulically, is not on high enough oil pressure at 600 rpm. But I don't even know if the tensioner is hydraulic.

Thoughts? People wonder if I have a diesel.

 

Unable to access the mpeg file - perhaps embed a link to a YouTube video might work.

 

The file is an mpeg-2.

Here's a mp3 (just the audio.

When the rpm rises, it goes up to 800 then 1000.

 

Mine makes a diesel rattle type sound sometimes that I thought was a timing chain issue brewing that also wasn't very obvious under the hood, but easy to hear in the cabin. It turned out that it was just the plastic engine cover vibrating and making noise (I think) where I've lost one of the spring clips that holds it in place.

 

From the sound of it - piston slap.
It might be worth correlating the sound to the bottom or top end with an engine stethoscope at idle. You can make one with a length of threaded rod and a piece of vacuum tube.

 

Wow! That's the air cleaner box, right? Will check it. Those are the exact symptoms - can't really hear it in the engine compartment but can with the hood closed and in the passenger compartment.

Prize for extremely worrisome possibility ... won! Compression is great, so I dunno ... but now you got me thinking. Have to narrow this down.

Thanks guys.

Any other ideas, I'm all ears. Heh.

 

you can count on me.

 

Note the sound is when the engine is warm, and is only at idle speeds. Fingers crossed - that kind of discounts piston slap, which ought to stick around for at least modest increase in rpm.

 

Well dammit, the sound definitely is coming from the bottom of the motor, and when I put a stethoscope on the bottom (the oil pan?) I hear a nice clear tick tick tick.

If it were timing chain slap, where on the front of the motor would I hear it?

The tensioner is a reasonably cheap replacement; is it difficult to swap out?

Note I found tiny grains of non magnetic crud on the oil filter media. I haven't been driving in sand, so it seems like that must be something from inside the motor.

 

It doesn't sound like that was your problem, but my noise comes from the big plastic cover on top of the engine.

Could the stuff you saw on the oil filter be from the bearings? They're coated with non-magnetic material and would be consistent with bottom end noise. Might be worth getting an oil analysis done so see if bearing material is excessive.

 

An oil analysis found excessive iron, but investigation revealed that the oil filter had disassembled itself and so was bypassing unfiltered oil.

The cylinder walls are also non magnetic material, but again, with good compression it's difficult to imagine that being the problem. I'll recover the filter media from the trash and wash it in solvent to try to identify the junk on the filter.

This noise has been present for quite a while. That and the fact the noise is only at idle speed - whatever's happening isn't happening very fast.

Dunno; if the motor is shot, the motor is shot and I'll likely just part the thing out.

 

What is the logic that rules out piston slap if the noise occurs when the engine is warm?

 

Iron - bearing material? If so I'll move from piston slap to rod knock. Either way, the bottom end of the motor will be knocking, lower so if the latter - piston slap you'll hear very loudly halfway up the block. You can rule out piston slap by cutting fuel or ignition to the suspect cylinder as piston slap is loudest under load. No load = less slap.

I hope we're all wrong here.

 

Good question. Back in the day, it would be because the pistons were aluminum and the block iron; with different rates of thermal expansion, the pistons would expand to fit the cylinder.

In this case both the pistons and the block are aluminum, at least I believe so, and the explanation would be that the pistons are hotter at operating temperature than is the block. The block is cooled by the coolant and is typically 100C, while the pistons are, at best, cooled by an oil spray from the underside.

 

Stethoscope reveals a definite engine-rpm-rate ticking. The sound in the video is clearly about 10/second, which corresponds to 600 rpm. I'm pretty sure it's the same noise heard outside; you just only hear the lower frequencies out in the air versus with the stethoscope.

Rod knock, though - I don't hear a thing when the motor is under load. If it weren't for the motor sounding like a diesel at idle, you'd never know anything is wrong.

I swept the filter media with a magnet and didn't pick up a bunch of junk. I only found the non magnetic stuff by visual inspection. I'm thinking the iron that Blackstone found was due to wear from the stuff not caught by the broken filter - and iron not filtered out. (Never buy a Bosch filter for this motor, by the way!)

Does the ECU even allow the motor to run with a cylinder disabled without going into limp mode? I would think it would freak out.

Me too.

 

Non-magnetic means nickel, bronze, chromium, aluminum and mineral (ceramic) correct? What components use these materials?

 

Could be plastic, too.

It wasn't any huge amount of stuff. Just a few grains.

Dunno. I just need this thing to get me on one last road trip. 900 miles. I wouldn't mind keeping it but don't want to have to dick around with towing out in the middle of nowhere.

 

CA to TX?

bring some seriously heavy oil if it is diagnosed to the lower end to cushion any out of tolerance internal clearances that are causing the noise.

 

Idaho! Part of the great Calexit.

I just might buy a bottle of gear oil. 75W-90 in ten quarts should boost the viscosity significantly.

I thought of something else indicating it's a sufficient oil pressure problem. It doesn't make the noise when cold, only warm. Thinner oil would make lower pressure on a leaky tensioner. Maybe I'm grasping at straws.

It's spooky; the thing runs beautifully at higher rpm. Smooth as silk.

I bought a tensioner and will swap it out when I do the belt and pulley - I'm trusting FCP Euro's notion that they should be changed.

 

How many miles do you have on your GL? I'm betting it will do just fine on your trip.

 

170K. Should be fine; I just worry a lot.

I just realized the tensioner is not oil charged. Rather, it's a ratcheting spring loaded mechanism. So much for that idea.

Tagging alx in; hope he can shed some light.

Audio files are from a mic under the car, cold start and fully warm, rising rpm.

I'm almost thinking it's something external to the motor.

 

I had a HELL of a time finding a noise that was not exactly like this, but similar. One day I tapped the drivers exhaust manifold and found the culprit. I dont have a video of the noise while running but here's what I found:

 

Fascinating. Thanks for sharing. Of course the M273 has a different exhaust, but this is worth investigating.

I didn't put the stethoscope on the exhaust. I think I was afraid of burning my ears or something.

 

Remove the Serpentine belt, run the engine for a few seconds. Listen for the noise.

If you don't hear it, that eliminates anything in the engine (piston slap, etc..) and points towards one of your pulley driven components (or a pulley itself).

If you DO still hear it.. well... good luck with that.

My 2 cents.

 

Removing the serpentine belt will help diagnose the sound, but in my view the belt doesn't need to be removed to identify a belt- or pulley-related noise. Spend a long time with the engine running listening and using the stethoscope.

Does the noise ever go away, ever? Or is it present 100% of the time, without exception?