Engine fumes

My daughter’s W-reg VW Golf MKIV 1.9 SDI is really fumey. I’ve fitted a new front-to-back exhaust and a front pipe including cat, centre and rear box. I’ve also removed the inlet and exhaust manifolds and have renewed all gaskets with VAG ones, including the manifold to down pipe, and cleaned the carbon out of inlet manifold. I have flushed and changed the oil and filter, the fuel and air filter and the pollen filter. None of this has had an effect. The car only passed its MOT last month, so exhaust emissions are OK. There are no leaks in the exhaust joints. Stephen Haywood As you have renewed and checked the exhaust system, I will discount the fact that a small leak in this area may be allowing fumes into the vehicle.

You do not mention the mileage of the vehicle but I am assuming from the age that it is most likely over 100,000 miles. My first check would be to ensure that the crankcase pressure is not too high. By removing the dipstick with the engine running, you should soon see if gases are being forced out under pressure. I would also ensure you do not have a fuel leak from any of the pipes around the engine; diesel falling onto a hot engine will cause pungent fumes.

I assume the fumes can be smelled from under the bonnet as well as in the vehicle. If this is not the case and the fumes are just in the vehicle, I would suspect it may be a leaking heater matrix. A small amount of antifreeze evaporating from the heater matrix will result in a powerful smell.