Visible smoke

QI would be grateful for your opinion on the two issues outlined below please.

1. My 2005 X-TYPE diesel estate purchased new, now having done 188,000 miles, recently had its MOT and annual service. The MOT was a fail on visible smoke from a vehicle fitted with a DPF. I pointed out that this was incorrect as the car was manufactured to Euro 4 (November 2004) and does not have a DPF fitted.

It should have failed on excessive metered smoke for a vehicle fitted with a turbocharger. This seems to me slightly less stringent than the DPF requirement? Be that as it may, it appears that it met the standard when idling but as soon as the throttle was opened it had difficulty meeting the standard. My Local Jag Centre

Man (LJCM) says it is probably turbo wear. Eventually it was passed after some internal cleaning combined with hard driving.

I don’t disagree with turbo wear as the likely cause, as the turbo has been on the car since it was new. So my question is: Is 188,000 miles a fair mileage for a turbo? Given the age of the car replacing with a new turbo would be way too expensive. What would your advice be as to the next best option?

2. Earlier this year I wrote to you about a resonance coming from the front of the car that I suspected was possibly caused by failed baffles in the exhaust system. LJCM thought that it the probable cause was failure of the rear engine mounting/support. The resonance built-up until about 50mph and didn’t get any worse at higher speeds.

Well, it turns out that one of the MOT advisories was ‘offside front wheel bearing noisy’. So I had this renewed and hey presto the resonance has gone. Presumably the vibration caused by the worn bearing was being transmitted up the driveshaft, etc? So all of us were wrong in this instance!

I was a bit surprised that it was the offside front wheel bearing as in my experience it is usually the nearside one that takes all the hammering from roadside potholes, gutters, kerb-stones, etc.

John Osley

AStarting with the diesel smoke test – I can understand why the MOT test centre would initially suspect that a DPF is fitted as the Autodata information would list the X-TYPE from 2003-2010 as having a Diesel Particulate Filter (DPF) fitted in the exhaust system. Although having said that, they would have had the opportunity to examine the vehicle and should have realised that this wasn’t the case.

188,000 miles is a fair term for a turbo to continue operating, but if the smoke were a result of turbo wear I would suspect that the smoke would be grey and the oil usage would have risen significantly.

The black smoke which causes the failure of the smoke test is normally caused by an imbalance in the air to fuel ratio – too much fuel to not enough air. This can be either too much fuel is being added, or there is not enough oxygen being supplied via the induction system to burn the fuel. The black smoke is full of particulates that normally would be burned as fuel.

It could be argued that a failing turbo would impede the airflow but given that the smoke level was reduced after cleaning and fast driving, I would suspect that the diesel system was more a contributing factor, than the turbo, and would possible suspect that the

EGR valve may be one component which would benefit from a system clean.

It may be worth using a system cleaner on a regular basis which could maintain the exhaust levels you have now achieved allowing the vehicle to continue to comply.

The noise from a hub bearing can travel through the vehicle and be very difficult to pin-point, as the wear had increased to the point that it could be felt on the MOT, this would have made the diagnosis much easier, but I know from experience that sometimes it is very difficult to locate the corner of the vehicle the noise is actually coming from.

I am pleased to hear in this instance that the problem has been remedied without having to carry out any unnecessary work.