Renault Megane Scenic II manual - resonance at 2000+ rpm, particularly as revs drop on gear changing

JohnW

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We've had this irritating resonance for several years and it is getting worse and worse. It's in the engine bay somewhere, not road speed dependent.

New engine mounts, a precautionary change, didn't fix it but it was less noisy for a while.

The local exhaust specialist is pretty sure it isn't the catalytic converter. He could have sold me a new one but didn't. Nice man!

It's partly a little bit like what Toyota HiLux utes sounded like on gear changes as the revs dropped when going from lower to higher gears.

I'm running short of ideas.

Has anyone experienced this on any of the Megane range? All thoughts very welcome, thanks.
 
sounds like the exhaust to me
you could try temporary disconnecting it to prove it
 
sounds like the exhaust to me
you could try temporary disconnecting it to prove it
Thanks Peter. Yes, my first thought too. But.... The grey-haired exhaust specialist spent quite a time on it, including a stethoscope, and reckoned the noise seemed to be further forward. It's the whole of the front end of the car body that resonates. He could be wrong of course but he reckoned it wasn't the exhaust and he would have benefitted from the opposite conclusion.....

The cat bolts more or less straight onto the exhaust manifold and the whole thing is a single welded stainless steel unit. You cut and rejoin to replace cat or muffler/resonator.

I'll post here when we sort it. I'm just about over putting up with it.

None of the Scenic owners I know personally have had this noise... Maybe it is why the previous (first) owner sold it.
 
Has this come on all of a sudden or has it been gradual John?

It also sounds like the exhaust to me, could be the mufflers innards slowly deteriorating.
 
Check that all exhaust mountings and re-inforcements, brackets etc around the engine itself are all connected and tightened.
 
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Just for interest, does it have a "watchamacallit" flywheel - with the built in harmonic balance spring?
I thought they were only on diesels, but I've seen one mentioned on a petrol engine.
If it does, it could be a possibility?

Try taking off most of the inlet ducting, that has built in resonance boxes, see what happens. (Besides the throaty noise).
 
Just for interest, does it have a "watchamacallit" flywheel - with the built in harmonic balance spring?
I thought they were only on diesels, but I've seen one mentioned on a petrol engine.
If it does, it could be a possibility?

Try taking off most of the inlet ducting, that has built in resonance boxes, see what happens. (Besides the throaty noise).
Yeah, dual mass flywheel. That’s my thought too… Yes, it has one.

Does it rattle at all from the bellhousing when idling?

The better outcome would be the harmonic balancer - put some whiteout on the outer and inner sections and see if it’s slipping. 2000rpm is about where second order vibrations are in inline 4 engines, and a dead harmonic balancer could do it…
 
Thanks for all the suggestions. All advice welcome.

It has a new clutch and therefore a new dual mass flywheel. It was 15 years of city driving old and definitely on the way out. Replacing it made zero difference.

Before the noise got worse (it's been progressing slowly for 4 years+) it was mostly above 3000 rpm but the band is widening.

It's definitely up at the front, the catalytic converter being the first potential culprit I agree. However the very experienced exhaust guy was very sure that it wasn't the cat. He also was adamant that it would have failed completely long before 4 years if it was starting to go.

My best guess/judgement for what to check next has been the induction system - it's in for service today. A lot of it is in underneath the battery box.
 
maybe heat shields ,tinwork around engine bay ,radiator and air con condenser / rad support panel. that are connected to engine by rubber hoses that can transmit vibration ,
 
Is it a vibration you're just hearing, or is it felt through the car?

My old Laguna 1 had a bit of harmonic at around 2000rpm (SOHC F3R engine) that was just a slight out of tolerance crankshaft or flywheel balance I think. A new harmonic balancer helped immensely but never 100% cured it.
 
We've had this irritating resonance for several years and it is getting worse and worse. It's in the engine bay somewhere, not road speed dependent.

New engine mounts, a precautionary change, didn't fix it but it was less noisy for a while.

The local exhaust specialist is pretty sure it isn't the catalytic converter. He could have sold me a new one but didn't. Nice man!

It's partly a little bit like what Toyota HiLux utes sounded like on gear changes as the revs dropped when going from lower to higher gears.

I'm running short of ideas.

Has anyone experienced this on any of the Megane range? All thoughts very welcome, thanks.
When i purchased my 2007 Meg 11 manual at 91,000 k it was in a sorry state engine and exhaust mount wise with rattles, vibrations and thumps.
Replaced all 4 engine mounts which made a huge difference and that made it easier to listen to exhaust rattles and vibrations.
To cut this short i replaced all exhaust mounts with brand names and that was the fix in my case. The exhaust mount rubbers while not not all physically broken loose their strength due to heat and age and are very cheap to buy. I would do that to eliminate the exhaust as an issue.
From memory i think the O2 wiring connection was very close to the exhaust heat shield which had to the tapped up to give more clearance.
That could be an issue in your case and worth checking.
With all the cheap options covered it may be more serious :mad:

Even with the low klm's on mine the rack ends (inners and outers) needed replacing at 60k and 91k respectively (Left then Right) which isn't a good sign. It had one careful owner and never on rough roads.
If you couldn't get 200-250 klm out of a Toyota their would be something wrong !

Alain
 
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It's the whole of the front end of the car body that resonates.
Just re-reading and noticed this.
That suggests to me that a source of vibration is being transmitted to the body, which is shaking. Not so much a particular item which is resonating, if you get my drift. I doubt if an intake resonance (just noise, really) would transfer to the whole body shaking, for instance.
The most obvious source would be the engine transmitting vibration to the body. As Haakon has alluded to, most 4 cylinder engines have an inherent mid range vibration, the reason some designs have used a balance shaft to minimise.
Other than the harmonic balancer, or a complete engine balance including the flywheel, probably not much can be done to stop any vibration, so one can only try to prevent/minimise the transmission of the vibration.
One other source of transmission, which I have experienced in the past, is the rigidity of the exhaust system between engine and body. There is probably a flexible joint under the engine area to help isolate the engine movement from the exhaust system further back. Maybe it is losing its flexibility - just a thought.
I guess the engine mounts are the main culprit, they have been replaced, but none of them are perfect. I guess you replaced with genuine mounts.
Can this resonance/vibration be replicated with the car stationary and revving the engine?
I will have a go with my Scenic to see what happens.
 
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When i purchased my 2007 Meg 11 manual at 91,000 k it was in a sorry state engine and exhaust mount wise with rattles, vibrations and thumps.
Replaced all 4 exhaust mounts which made a huge difference and that made it easier to listen to exhaust rattles and vibrations.
To cut this short i replaced all exhaust mounts with brand names and that was the fix in my case. The exhaust mount rubbers while not not all physically broken loose their strength due to heat and age and are very cheap to buy. I would do that to eliminate the exhaust as an issue.
From memory i think the O2 wiring connection was very close to the exhaust heat shield which had to the tapped up to give more clearance.
That could be an issue in your case and worth checking.
With all the cheap options covered it may be more serious :mad:

Even with the low klm's on mine the rack ends (inners and outers) needed replacing at 60k and 91k respectively (Left then Right) which isn't a good sign. It had one careful owner and never on rough roads.
If you couldn't get 200-250 klm out of a Toyota their would be something wrong

Alain
Thanks for that.
 
Just re-reading and noticed this.
That suggests to me that a source of vibration is being transmitted to the body, which is shaking. Not so much a particular item which is resonating, if you get my drift. I doubt if an intake resonance (just noise, really) would transfer to the whole body shaking, for instance.
The most obvious source would be the engine transmitting vibration to the body. As Haakon has alluded to, most 4 cylinder engines have an inherent mid range vibration, the reason some designs have used a balance shaft to minimise.
Other than the harmonic balancer, or a complete engine balance including the flywheel, probably not much can be done to stop any vibration, so one can only try to prevent/minimise the transmission of the vibration.
One other source of transmission, which I have experienced in the past, is the rigidity of the exhaust system between engine and body. There is probably a flexible joint under the engine area to help isolate the engine movement from the exhaust system further back. Maybe it is losing its flexibility - just a thought.
I guess the engine mounts are the main culprit, they have been replaced, but none of them are perfect. I guess you replaced with genuine mounts.
Can this resonance/vibration be replicated with the car stationary and revving the engine?
I will have a go with my Scenic to see what happens.
Thanks for these comments. Interestingly, the noise was almost absent when I drove out this morning but 20 minutes and 10 km later it was back with a vengeance. Yes, reproduces perfectly just bringing up the engine revs when stationary. When driving, declutching and the noise disappears completely.

It had a full set of correct new mounts (Eurocare) and for a little while the noise was much subdued in volume but still there.

I reckon something under there is just touching and transmits the noise when IT resonates. Sometimes it sounds like a rubbing "swiff - swiff - swiff" too but that disappears on declutching too.

Sometimes I wish I had a hoist but that would necessitate some serious building and probably a justifiable divorce!! :)

Still it is interesting.....
 
There is also an exhaust heat shield near the fuel filter where the pipe bends around the fuel tank that catches stones from the front wheel and can bend against the exhaust pipe. Its very thin aloominum sheeting and bends back out easily.
 
Interestingly, the noise was almost absent when I drove out this morning but 20 minutes and 10 km later it was back with a vengeance.
Thats the exhaust system heating up and expanding perhaps ;) Check the middle mount particularly for condition and for correct adjustment ( its right behind the front muffler). I noticed that on my scenic it had failed and was hanging on the nylon safety cord, but it was also not correctly aligned laterally and was jammed against the side stop. You'll see what I mean when you get under there, but the mount allows for the exhaust to move around a bit.
 
Thats the exhaust system heating up and expanding perhaps ;) Check the middle mount particularly for condition and for correct adjustment ( its right behind the front muffler). I noticed that on my scenic it had failed and was hanging on the nylon safety cord, but it was also not correctly aligned laterally and was jammed against the side stop. You'll see what I mean when you get under there, but the mount allows for the exhaust to move around a bit.
Thanks for that detail. I'll have to find it as it is getting bad for my health.

Yes, no question something is heating and presumably expanding. Hmm. What's long and gets hot.......?? Hmm..... It was a marked change this morning, more than I'd noticed before. I wish something would just do the decent thing and break!
 
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