Aygo Engine Intermittent Metallic Rattle On Idle - Help Please!

[johnny01]

Hi to the Aygo club!

On my recommendation a friend of mine has bought a used Aygo from Mr T, a really lovely example, 2008 with full Mr T service history, only 20K on the clock and 3 months warranty. All was well for about a month then one night after work we were defrosting when we noticed a metallic rattling coming from the engine. It is a very distinct and noticeable rattle with the following traits:

1. It is intermittent, appears after about 10% of start ups

2. The rattle is only evident at idle - if the accelerator is lightly touched to bring the revs up a fraction it disappears

3. It only appears to rattle on start-up, it has never started rattling during a journey or when the engine warms up for example

4. Sometimes the rattle stops after a short journey, sometimes not

5. It might be cold-related, only because the temperature now is colder than when the car was bought and it was first noticed during minus temperatures. However, the rattle has also appeared when it has been simply 'cold' and not 'frozen'.

The car has a full Mr T service history, and was serviced by the main dealer before delivery to my friend. It has been sat at my local Mr T for 3 days and they have left the car outside and started it several times without the rattling appearing. To be fair to them they are trying their best but without the fault manifesting itself I'm not sure what else they can do.

The warranty runs out in 5 weeks so we're a little anxious that if nothing is found before then, we might end up with a bill for engine work or God-forbid a broken engine. It's been many years since I've worked on engines, but to me it sounds like timing chain tensioner not having enough oil pressure on idle when cold. The sound certainly appears to be coming from the 'auxiliary belt' side of the engine, and my local Mr T have had a poke about and everything seems OK externally, including the water pump.

Any thoughts or advice would be helpful - does anyone have experience of this?

Many thanks - John

[Raistlin]

Is your oil level correct ?

[SandyCat]

Exhaust heat shield?

[johnny01]

Oil level is at maximum and it's not the heat shield, it's definately mechanical and internal with a regular rhythm to it. It could be mistaken for noisy tappets because of the rhythm of the sound, but it has more of a metallic 'ring' to it than the dull clack of a tappet and it appears to be coming from the left hand side of the engine as you look at it from the front, possibly low down. Like a loose timing chain. :(

[uli]

This problem was also discussed on the German Aygo forum. It has got something to do with the "Ventilspiel" that is valve variance(sorry for my bad translation) and it`s nothing to worry about as long as this phenomenon occurs when the engine is cold.

If it occured when the engine was warmed-up you would have a problem.

It seems to be widespread with the Aygo.

Because the engine is made of aluminium the sound is metallic.

[johnny01]

This problem was also discussed on the German Aygo forum. It has got something to do with the "Ventilspiel" that is valve variance(sorry for my bad translation) and it`s nothing to worry about as long as this phenomenon occurs when the engine is cold.

If it occured when the engine was warmed-up you would have a problem.

It seems to be widespread with the Aygo.

Because the engine is made of aluminium the sound is metallic.

Interesting... Has anyone else had this problem? I don't dispute this has happened, but if it's widespread with the Aygo there should be occurences of it in the UK too. However, it doesn't sound like valves, the sound itself is too 'random' for that, like something is loose. When people hear it they say "Ouch, something is wrong with your engine!" My own Aygo engine is a little noisy/tappety when cold and on idle (under 10,000 miles) but this engine, when the rattling occurs, sounds nothing like mine at all.

I must try and obtain a recording - imagine someone rattling the blade of a screwdriver inside the engine casing, down the left hand side (not across the top of the engine where the valves are) and it sort of sounds like that. And it's not quiet either, almost three or four times louder than the usual idle noises. I'm not convinced everything is OK...

[SandyCat]

Thinking about this I wonder if it's what I heard the other day. We have only had the car a short while and I am not always there when she starts it but I did hear it a few days ago and remember thinking it sounded a bit rough like an engine that had done more miles than it has done and I thought it will sound better when I get It serviced etc. but maybe this is actually normally when it's cold.

[Valvematic]

timing chain perhaps?

[johnny01]

As per my first post I think it's the tensioner - if the timing chain had issues the sound would be present all the time, I'm guessing. A stab in the dark would be the lower oil pressure on idle coupled with thick oil when cold not being able to sufficiently pressurize the tensioner. I've been told it's a very small hole the oil has to travel up in order for the tensioner to work.

Any official Mr T or experience mechanics out there care to hazard a guess?

PS: The car is back with its owner, the fault having failed to appear at Mr T