C36 - diesel 'klatta-klatta' noise at idle

[silversixx]

Hello all,

I recently acquired a '96 C36 AMG with 65,000 documented miles. It's my first Mercedes-Benz and so far I'm very happy with it on the whole.

I've replaced the oil, filters, plugs, coolant, serpentine belt and pulley and as far as I can tell the car performs as it should with plenty of power. After 2000 miles it has used no oil or coolant and is returning in the region of 25mpg.

The thing is... as soon as the motor is no longer cold (i.e after a few minutes of running and long before it is properly warm) and at a standstill, it sounds like a really smooth modern diesel motor at idle with that distinctive 'klatta-klatta' sound. As you pull away, at about 1900 rpm the noise vanishes as if a switch has been flicked.

My initial guess was that this could possibly be the chain tensioner, but the tensioner is located quite far down at the front of the motor whereas the noise seems loudest at the fuel rail/inlet cam area. The local MB dealer could only suggest 'dismantling the motor to see if we can find anything'. I politely declined!

Looking online, across the world people with C36's report the same thing and have a whole host of explanations: the special Mahle (as opposed to Kolbenschmidt in all other MB sixes at the time) pistons, the tensioner, the chain, excessive cam wear etc etc... Everyone seems happy to live with it and some report that the noise has been there for many thousands of happy and reliable miles. The only case I found where the sound was made to go away was when someone connected some sort of module to their car which allowed them to swith the inlet-cam variator on at idle. Some other guy reckoned that if you get out there and thrash the living daylights out of the car down the motorway for 20 mins then it would go away, but that's not really my way of resolving the problem!

Does anyone here have an opinion as to what could be causing the noise? It's not that bad, and all signs are that it's not causing any harm at all, it's just...not what I expected from a Mercedes-Benz and I'd love to get to the bottom of it.

Of slightly less irritating nature is a 'vacuum cleaner' sound from under the bonnet which accompanies the engines RPM and gets louder as the revs rise. The only adverse effect of this is that it gets so loud at mid-to-high revs, I can't hear the lovely sound that the motor is probably producing!

If anyone can help me with either issue then you'd be helping me to transform a surprisingly-enjoyable first-time Mercedes-Benz experience into a great one, and I'd be in your debt.

 

[ant500sl]

The inlet camshaft has a variable valve timing mechanism that advances the timing by mechanical means. There are several toothed gears that move together and advance the inlet timing at certain revs.

Due to the spec of the engine the advance is 18 degrees whereas the advance on regular 2.8 and 3.2 litres is 28 degrees or more. To get this lower level of advance a sleeve is built into the timing mechanism which restricts the movement of the gear. Unfortunately this reduces the contact area on the teeth and the gear rattles when the oil warms up due to the lower pressure acting on it.

I am in the process of experimenting with mine as a factory replacement is about £1200!

V8 engines with the same timing mechanism have an extra spring to hold the gear in place at idle as in early engines it was found that a rattle developed on starting and when warmed up in hotter climates. Hopefully when I have time over Christmas I will attempt to retrofit a spring from the v8 and see what happens. Got a spare engine just in case!

As for the hoover noise it is most likely the fan as it shifts quite a lot of air, it should stop above about 3k rpm with a warm engine. Also the engine will not rev beyond 4k rpm when in park or neutral as a protective measure for the gearbox, and is not a fault as I first thought.

Pound for pound I think they are one of the best cars on the road, fortunately few people know about them which keeps the prices down.

 

[television]

We have the same issue running here as well

http://forums.mercedesclub.org.uk/showthread.php?t=44013

Welcome to the forum

 

[HERBIEMERCMAN]

hi silversixx, i have an e-300 td.esta. 1997,just had the injectors fully tested and serviced to improve the spray patterns,for performance and ecconomy, vehicle had covered 190k miles before the work was done. soon after the work was completed i developed a clattering noise at 1200 rpm, noise stopped at any higher rpm. "merlin diesels" at walton summit, nr. preston said this was not the timing chain as i thought, it is a faulty injector or injectors. they say they will resolve the problem this thursday. £100 plus parts.

 

[kth286]

Hello all,




The thing is... as soon as the motor is no longer cold (i.e after a few minutes of running and long before it is properly warm) and at a standstill, it sounds like a really smooth modern diesel motor at idle with that distinctive 'klatta-klatta' sound.

It is probably the tappets not properly filled with oil.

Are you using fully synthetic of correct viscosity ?

What is the oil pressure gauge showing when this happens.

 

[silversixx]

Hi ant500sl, that's an interesting angle. Please let me know how you get on with the extra spring. I'll go and have a play with the fan shortly - I guess I could unbolt it from the pulley and run the motor briefly without it to see if that's the 'hoover' noise at revs?

Hi television, thanks for the link. I did try a search for the topic but didn't see it.

Hi HERBIEMERCMAN, do you think that less-than-ideal injector condition could cause such a noise with a petrol motor? The car goes like a buttered pig so it's hard for me to tell if they're not quite as they should be!

Hi kth286, that's interesting. First of all my C36 has no oil pressure gauge (should it have?), although in my experience just about any properly-warm motor will show a very low reading at-or-near idle. My local M-B specialist (all ex-M-B staff) insisted that I run Mobil 1. When I was racing cars this stuff was useless but they swear that the C36 was designed to use it so...in it went (£££ how much?!?!?! £££). Of course I fitted a new filter as well and when I started the car up it made a horrific 'diesel' noise for just the first half-second or so, and then immediately sounded fine (as it always does when cold) so I suppose it was filling a drained tappett. Could the noise be insufficiently-filled tappets when the oil is warm and the rpm very low??

Thank you all for your help, I guess the right thing to do is move to the link that television gave me and carry on there?

Cheers

 

[ant500sl]

One other thing that springs to mind is using a thicker oil. As you mention Mobil 1 was recommended by Mercedes but I think this may have been more of a corporate sales thing as every car I have had with a factory performance engine has called for 10w60 or similar. In a hot engine Mobil 1 ends up like water as you will know from your racing days. Can't beat a bit of good old castor oil!

Due an oil change so I think I will try the castrol rs 10w60 I use for the jaguar and see what happens. Alot easier than changing the cam adjuster.

The fans are a nightmare to get off without the special tool, could you describe the noise you are getting?

I do all my own work on my cars so my experiences are first hand. I don't post very often as I spent most of my spare time working on the things rather than talking about them. Finding someone with an identical problem inspired me to post my expeiences.

A few other points. The C36 was never fitted with an oil pressure gauge. Tappets are more of a clickity click! As I have the identical klatta-klatta noise on my car I am pretty sure your problems are camshaft adjuster related.

If you apply 12 volts + to the terminal on the cam adjuster and - to the other terminal the engine should idle slightly rough but the noise should disappear as the chamber that operates the adjuster will fill with pressurised oil and advance the timing. This takes up the play in the adjuster and stops the clatter. The adjuster is actuated by the ecu while driving at about the 1900rpm mark which is why the noise suddenly disappears, you are just replicating it at idle which will not harm the engine.

 

[HERBIEMERCMAN]

hi silversixx, my friend works at merlin diesels he says he has only experienced the clattering noise on diesels, the petrol injection operating charachteristics are different. the only parallel in my experience on a petrol engine would be "pinking" caused by timing and carbon deposites in the combustion chambers. best of luck. herbiemercman.