- My model of MX-5 is: NC
- I’m based near: Chelmsford
- I’m looking for technical help or recommendations on: Engine noise on startup
Hi,
I thought this issue was resolved by changing the idler and tensioner pulley, but it still seems to be there. It is a rattling sound on startup and under some acceleration. There doesn’t seem to be a pattern with the acceleration rattle. Sometimes it can be bad, sometimes not that bad. Took it in for an MOT and it was horrific on the way back, phoned up and got it looked at afterwards and there was no sound driving back to them. They couldn’t reproduce it either.
Some videos of it starting up here, all with the serpentine belt off. Very hard to do with acceleration because it has no rhyme or reason to it.
It was quite bad last week, and the clutch was spongy. Halfway coming home the clutch went solid again and the sound was gone from acceleration. I replaced the master and slave cylinder and this has made the clutch feel much better, but hasn’t changed the noise.
I’m not sure about anyone else but it sounds pretty normal to me.
The sounds clips are either too short no-where near the engine or have wind interference.
How old is it?
Does it use oil?
Has the oil been changed recently?
Have you had the car long?
The sounds clips are either too short no-where near the engine or have wind interference.
The sound only happens for the first 1/2 a second after the engine turns on. It sounds like a short and loud tapping/clicking/knocking, you can hear it in all the clips pretty clearly after the engine catches. I didn’t record past that because idle there is no noise, and the belt wasn’t on the engine.
How old is it?
2008 NC1.
Does it use oil?
Between 1/4 to 1/2 litre per 1000 miles. That seems to be the norm from what I have seen.
Has the oil been changed recently?
Oil was changed about 9 months ago.
Have you had the car long?
About 9 months as well, didn’t get to drive it much over winter and only started noticing it recently. 2 garages said they could replicate the sound driving, but not on the lifts.
I thought I should also mention it revs competely fine normally when in neutral, only with load is there a chance of the rattling noise
So it does this on consecutive startups with no lengthy (say 1/2 or an hour) between attempts?
It does this on any startup, warm or cold. Doesn’t matter if clutch is in or out either.
Someone else pointed out to me that it also does that sound if I release the clutch quickly when changing gears. There is some vibration in the car so I was thinking maybe engine mount, but I have no idea. I don’t think it is rod knock because it comes and goes when driving.
Yes, but answer the question posed please.
This one?
So it does this on consecutive startups with no lengthy (say 1/2 or an hour) between attempts?
It does it on every startup, warm or cold, doesn’t matter the time inbetween.
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Process of elimination dear Watson 
It isn’t start up rattle then. That only occurs when it’s been left a while for the oil to drain from the VVT actuator.
It’s notoriously difficult to diagnose engines via sound clips without standing by them, but I would remove the oil filter, cut it open and unravel the paper element, see if it has any small shiny flakes in it.
Gotcha, I will do that tomorrow. I checked the oil level today and it was about midway up the stick and goldy brown.
Ok, fingers crossed for a clean filter.
It’s using oil which isn’t a good sign, but rod or big end knock is not binary, it totally depends on how much of the bearing surface has been removed and the conditions.
I once had a guy pick his car up after some non engine related work doing. As he was backing out the workshop I said ‘your engines knocking’. He said ‘Well I can’t hear it?’ It was very mild, but I couldn’t understand how he couldn’t as i’m going deaf and he was 20yrs my junior. He said he had a trackday booked and I said well you’d better be careful or cancel it. If I hadn’t noticed he’d have wrecked his engine with a rod coming out the block. As it was we saved it by simply replacing the bearing shells (it wasn’t caused by oil starvation, but by a dodgy turbo build) and getting the engine mapped properly.
To cut a long story short don’t get me to tune your piano.
Are you aware of this TSB? The VIN numbers won’t correspond to a UK car but the concern might.
I see it’s a 2008 model.
Read through and couldn’t see the mileage.
Uses oil.
Rattling not just on start up.
You have a cam chain.
Involved with that is obviously the chain.
Also is a tensioner and chain guard rails.
Now “if” your chain and other bits are worn then that would cause rattling, (but not heard on your video’s).
Also the cam gears are more than likely to be worn too.
It would certainly be worth checking all that as part of the process of elimination.
(Complete kits available).
Just my opinion which may help.
PS-The sound clips don’t shed any light on the matter, (for me anyway).
Am I missing something??
Surely the oil level being halfway between min and max is no proof that the engine uses oil unless we know for sure that it was filled to the max level, which it may not have been.
The OP stated he changed it 9 months ago and it uses “Between 1/4 to 1/2 litre per 1000 miles”.
So by that reckoning it could use 4 litres in around 8000-10000 miles. 
Which in my opinion is “Rather Excessive” to say the least.
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Ah, didn’t read it closely enough, so I was missing something.
Thanks.
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The car has just over 50k miles. I asked my mate how much he had filled it up because he had the car for a day when he did. (I double checked the oil after and it was at the correct level). He went and checked the container and he used hardly any. So not 1/4L per 1000 miles. I haven’t filled it up since then, but I also haven’t put down many miles on it.
I wasn’t able to remove the oil filter today because I had to move it somewhere I would be able to lift it up. I did however get a video of it turning on, idling, and revving. The car was off less than 2 minutes before this was taken. https://photos.app.goo.gl/NgKGNXgN6Gdnqt1n7. I might try to get a better video later because the audio only seems to be right ear only for sections.
Okay, having listened to that audio file, in my opinion not big end related, (as it’s as you say a rattle).
You have checked, changed other pulley’s belts and it’s still there.
As I said before my “Best Guess” would be cam chain rattle.
As you can hear it (25 seconds into the clip) sort of “Bouncing/touching” on other components if you get my drift.
It may be that the tensioner is/has starting to fail seized.
BUT I could be wrong.
Good luck.
After having a listen at other peoples cars, that does sound like what it is. The part doesn’t look expensive, but the repair does look complicated to do. Might have to get the garage to do this one.
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