My new ND MX-5 makes a very slight rattle noise on a cold start. I can’t tell if it is meant to do it or not.
It isn’t bad enough that I know it is definitely wrong but at the same time just want to make sure if it isn’t right it gets sorted.
Anyone else experience this in theirs?
Good morning,
never any sign of a rattle from my ND at 10,000 miles now. Can you narrow it down to engine, clutch, gearbox?
To me sounds more like the engine, more noticeable at the engine end and then a bit quieter at the exhaust end. I will try and upload a video. As I said it is only on cold start, once warm no noise at all.
I have just come from a BMW M140i, which a lot suffered from exhaust rattle, however this was due to the valve in the exhaust pipe rattling which obviously the MX-5 doesn’t have.
Is your new ND 1.5 or 2.00 litre?
2.0 Sport Nav Soft Top
They all make a very unusual and ‘strange’ noise when first started from cold but it only lasts for 10 seconds or so and is ‘normal’. I would not describe it as a ‘rattle’ though.
There is an aluminium cover over the exhaust manifold in the engine bay. ONLY when the car is COLD make sure it is secure by giving it a little wiggle. One of the bolts on ours was not gripping it so I took the bolt out and twisted the shield slightly so it nipped it when the bolt was replaced.
My 1.5 hasn’t got any engine rattle so far although the unit revs quite high at start up and is generally fairly noisy before settling down.
Interesting you came from a 140i as we have just bought a new one and I have read all about the famous exhaust flap rattle!
Are you sure it is a rattle as such. The ND makes a strange noise and sounds pretty rough on cold starts. It is something to do with the emission control (bleeding air into the exhaust system) and is quite normal. The noise goes away after about 15 to 30 seconds.
Judging by your responses it could be that it is entirely normal. Just making sure it’s nothing serious,
Seems the only thing wrong with the car is how little it’s been driven. Had it almost a week already and still only 114 miles on the clock
Yes, I get this vibro-rattle on start-up when engine is completely cold - seems to be from front end of exhaust system, and goes when revs drop after 20 seconds or so. I was going to ask the dealer about it when I visit them next, but it would appear from replies as above that it is ‘normal’. However, in the meantime, I’ll give the aluminium shield a wiggle as per Mad Malc’s advice.
I wish I could recall where I read an interesting article ages ago. Might have been Miatia.net.
To my surprise it was included in some Mx5 fuel consumption thread (I think) and someone connected with Mazda “informed” the thread that the SkyActive, amongst many other modern mills, have the combustion chamber tolerances, crank bearings “engineered” to be slacker frfom cold than old school to reduce friction losses but when at full working temps, piston rings etc tighten up to full compression tolerances. Now, this immediately flagged up to me the potential for a cold engine to sound a bit “loose” and lashy. You’d think, for a start, you’d see some emissions from the exhaust?
If I have a light bulb moment and recall the link I’ll post it up. It was years back.
2.0 SportNav here. Yes I confirm the sound on mine. Rather a wheezing sound like the start of a hole in the exhaust or a leaking valve. Does sound like it is running a bit rough but firing on all cylinders. I had no idea what it was but the description by ‘First rider off’ of the emission system bleeding air into the exhaust would make a lot of sense. Mine stops after around 10-15 seconds as I start to move off. The change is as if somebody has put their finger over the hole that was leaking air.
I think you have just found the question that everyone was afraid to ask. A bit of shared knowledge has put everyone’s mind at rest.
Thanks
I know they now use much shorter pistons (which will tend to increase piston “slap” when cold) with low friction coatings to reduce friction but I very much doubt they have larger (slacker) crankshaft main and and big end bearings. These bearings rely on hydrodynamic lubrication effects to create a running high pressure lubricating film of oil to provide clearance between the crankshaft and the mating white metal bearing surfaces. These rely on the oil pump getting oil through the crankshaft oil ways to the bearing surfaces and the residual thin film of oil lubrication on initial starting to prevent seizure, but once rotating it is hydrodynamic oil pressure which keeps the rotating surfaces apart. If initial clearances are too large it would take much longer to create the hydrodynamic pressure (if at all) to keep the rotating surfaces apart under high loads and the horrendous main bearing failure knocking would occur. As for piston rings, they create a seal due to their elasticity (springiness)and temperature has very little effect on the friction they create. Again they tend to use a hydrodynamic effect to maintain lubrication and again during start up there is some possibility for metal to metal contact but modern engines use low friction surface coatings on the rings to prevent galling and seizure during starting.
I think first rider off has the answer. The new Skyactiv petrol engines have a 4 2 1 exhaust system which places the cat a long way down the system and takes a while to light off. To improve the initial emissions on cold start the ECM retards the ignition timing and changes the injector timing to get hotter exhaust gases to the cat earlier. The result is what may be heard or felt as rough running for maybe 15 to 20 seconds and also a higher initial idle speed than normal engines.
Interesting - I don’t hear a rattle on my ND 2 ltr , but an intrusive , gassy blare for the first 15-20 seconds on cold starts . I put it down as a character trait I can just about tolerate , unlike the ridiculous 'look at me ’ blip in revs on start up . Even on an Aston Martin V8 such a blip is borderline adolescent, but on a generic 16 valve four (ie like nearly every other modern Japanese car ) it sounds plain daft .
I don’t mind the blip, but I would draw the line at the loud spitting crackle that was programmed into a Jag F-type convertible I drove a while back. Starting it up on Thame high street on a busy Saturday I felt a right prat. It can be turned off apparently.
Arguably the blip is less adolescent than replacing a perfectly good standard exhaust with one that makes more noise
I haven’t noticed a rattle on my 1.5; but it does run roughly at an elevated tickover for the first few seconds - I assume it is doing something with the spark timing/injection to get itself going.