Could it be the tyres? - Update 19/01/16

[Big A]

I have a 2005 X3 2.0d Sport and since getting it back in August it was clunking and making noises which after a google all results seemed to point to having mismatched tyres.  I checked this with my mate who runs a tyre fitters and he confirmed that this is a common problem with X3's and also Subaru's, that they need a full set of matching tyres.  So with mine having 3 different makes of tyres I got myself a set of practically brand new partworn Dunlop SP M3 Wintersports.  Unfortunately, one of them was a 3D and not M3 tread pattern so put them on anyway thinking they would be better than the budgets and single Pirelli Scorpion that were on it originally.  The Dunlops did take the clunking noise away under braking and slightly away when accelerating, but the acceleration is really jerky now - even the rev counter jumps in steps instead of smoothly sweeping up.  It is also hesitant when accelerating hard with gradual low power then a sudden burst of acceleration, although this is not always the case and can sometimes pull like a train with no problems. 

The car has had its swirl flaps removed, oil separator changed to the vortex type and also the EGR/DPF and manifold cleaned up and was running great until the tyre swap, although always had a kind of lumpy idle until up to temperature.

Do you guys think this is a coincidence this started happening once the tyres were changed and purely down to just the tyres or that it could be the air flow sensor or something engine related?

[jagr]

Tyres should be BMW rated with a star on them '*'

Are you sure the thermostats are working correctly?

Have you changed the fuel filter?

[Big A]

Will be investing in some Pirelli Scorpion Verdes within the next week I think.

Not sure about thermostats. The temp gauge takes ages to get to normal and even then sometimes sits below centre even after a long drive.

Th car was serviced just the week I bought it but not sure if fuel filter was done. It is on the to do list though when I get it serviced again within the next few months.

[X5Sport]

Certainly sounds like a thermostat issue as these cars normally warm up pretty quick.  The rough running could be caused by part of the system being in 'cold' mode which will affect performance.

[Big A]

Is this the thing I'd be after?

http://www.ebay.co.uk/itm/BMW-X3-E83-2- ... SwofxUgcdN

[jagr]

I read a lot of posts online about failures with non genuine thermostats so chose to buy mine from BMW, it will be more expensive but probably cheaper in the long run.
I would always prefer to buy once.

[Big A]

If the thermostat was knackered would it still allow the car to get up to temperature?

Temperature was reading perfect 5 mins ago.

[Horizon]

If the thermostat is sticking, it can get up to temperature ok, but when you are driving down the road and lots of cold air is passing over the radiator usually the thermostat will close again preventing over cooling. Then once the temp reaches a certain temperature will reopen and allow coolant to recirculate around the radiator.
If the thermostat sticks open over cooling will happen, and cause the temperature to drop on the gauge.
You will find in traffic the temp will be up there at halfway.
When cruising down the road the temp will drop

[Big A]

Thanks.  Yeah, have found that when driving the gauge doesn't get halfway but when sitting with engine running or in traffic it goes normal.  Is changing the thermostat an easy job?

[mikesmith2939]

The egr valve thermostat is very easy.

The main one is a bit more involved but should take no more than hour from start to finish

[Big A]

Guessing it'll be the main thermostat that'll be knackered and not the EGR stat? Or would it be both?

[Big A]

Fitted a brand new set of star rated Pirelli Scorpion STR on Saturday and they have totally transformed the car!  The ride is almost silent, bumps don't feel as harsh and more importantly no knocking noises or jerkiness and smooth power delivery again.  What a difference!  Just need to sort my thermostats now to stop the lumpy idle when cold.

[kkglcivic]

ive just put a full set of tyres on mine NOT star rated and has also copletly changed the ride, clunking noise from transfer case has gone too

[X5Sport]

[quote="kkglcivic"]
ive just put a full set of tyres on mine NOT star rated and has also copletly changed the ride, clunking noise from transfer case has gone too
[/quote]

And yours is a?