Fan making really loud noise after engine turned off

[dperk2015]

This happened yesterday, had few people in the car. Dropped them off at a house, when I turned off engine I noticed a loud noise coming form the front of the car. It sounded like the fan trying to cool down or something, also the exhaust was boiling hot too.

I didn't get a chance to go back to the dealers to ask about this, but it really did sound like the car was going to explode. This lasted for about 15-20 mins or so and then stopped. I've only thad the car for 2 weeks, it's a year old. I put new 18" alloys on and chrome trim exhaust tip (very tight fit). Surely they couldn't effect the car like that?

Before I go back to the dealer, I just wanted to ask if anyone had any experience with this?

 

[Stripey]

This happened yesterday, had few people in the car. Dropped them off at a house, when I turned off engine I noticed a loud noise coming form the front of the car. It sounded like the fan trying to cool down or something, also the exhaust was boiling hot too.

I didn't get a chance to go back to the dealers to ask about this, but it really did sound like the car was going to explode. This lasted for about 15-20 mins or so and then stopped. I've only thad the car for 2 weeks, it's a year old. I put new 18" alloys on and chrome trim exhaust tip (very tight fit). Surely they couldn't effect the car like that?

Before I go back to the dealer, I just wanted to ask if anyone had any experience with this?

More than likely a regeneration of the DPF had recently taken place and the fan stays on to cool the bits down.

http://www.golfmk7.com/forums/showthread.php?t=2343

 

[dperk2015]

Had a good read through, thanks for that. I predominantly drive short journeys. It's something that I really never heard of. The dealer never mentioned a thing about it, so I think I'll give them a call just to have a chat about it.

 

[Sootchucker]

If you do predominantly only short distances, chances are the DPF will never fully finish a regeneration process. Basically the DPF (or Diesel Particulate Filter) on pretty much all modern diesels is there to trap all the crap that diesels used to emit from the exhaust (i.e. soot and nitrous oxide). The job of the DPF is to contain the soot within a canister and when it reaches a certain volume (in grams), the engine ECU will instigate a DPF regen.

In this mode additional fuel is injected into the cylinders by the ECU and all Eco routines are shut off (stop start for instance), in an attempt to get the engine and more importantly the exhaust manifold and DPF unit up to super high temperatures (over 850°C), so that the soot can be re ingested by the engine and at these high temperatures most of it burnt off.

To achieve these temperatures however, the engine obviously has to arrive at normal operating temperature and then some time afterwards to raise the temp further and actually conduct the DPF cycle (which can be as long as 15 minutes once temp is reached).

If you are only ever doing short journeys, it's advisable at the weekends to give the car a good run at at least 2.5k revs, on say a motorway or dual carriageway, to allow the DPF regen to finish and the canister empty again. It should be noted that the amount of soot allowed in the canister is carefully monitored, and if multiple regens fail, a warning light may come on the dash, and in severe cases a workshop visit may be required so that they can instigate an active regen using their workshop diagnostic equipment (which is chargeable BTW - not under warranty). In extreme cases where the owner ignores the lights on the dash and continues to drive the car, the DPF may reach saturation point (I think it's around the 90% full mark), after which the DPF might not be able to be saved and will require replacement (this could be a four figure sum to do) !

This is why, normally, diesels shouldn't' really be used for very short journeys unless you can factor in some playtime blasts to bring the DPF back to health. For inner cities etc., it's normally recommended to stick with petrol. Obviously these are just guidelines, and your driving style and lifestyle will ultimately dictate the type of engine most suitable for you.

 

[dperk2015]

If you do predominantly only short distances, chances are the DPF will never fully finish a regeneration process. Basically the DPF (or Diesel Particulate Filter) on pretty much all modern diesels is there to trap all the crap that diesels used to emit from the exhaust (i.e. soot and nitrous oxide). The job of the DPF is to contain the soot within a canister and when it reaches a certain volume (in grams), the engine ECU will instigate a DPF regen.

In this mode additional fuel is injected into the cylinders by the ECU and all Eco routines are shut off (stop start for instance), in an attempt to get the engine and more importantly the exhaust manifold and DPF unit up to super high temperatures (over 850°C), so that the soot can be re ingested by the engine and at these high temperatures most of it burnt off.

To achieve these temperatures however, the engine obviously has to arrive at normal operating temperature and then some time afterwards to raise the temp further and actually conduct the DPF cycle (which can be as long as 15 minutes once temp is reached).

If you are only ever doing short journeys, it's advisable at the weekends to give the car a good run at at least 2.5k revs, on say a motorway or dual carriageway, to allow the DPF regen to finish and the canister empty again. It should be noted that the amount of soot allowed in the canister is carefully monitored, and if multiple regens fail, a warning light may come on the dash, and in severe cases a workshop visit may be required so that they can instigate an active regen using their workshop diagnostic equipment (which is chargeable BTW - not under warranty). In extreme cases where the owner ignores the lights on the dash and continues to drive the car, the DPF may reach saturation point (I think it's around the 90% full mark), after which the DPF might not be able to be saved and will require replacement (this could be a four figure sum to do) !

This is why, normally, diesels shouldn't' really be used for very short journeys unless you can factor in some playtime blasts to bring the DPF back to health. For inner cities etc., it's normally recommended to stick with petrol. Obviously these are just guidelines, and your driving style and lifestyle will ultimately dictate the type of engine most suitable for you.

Thanks very much for all that info. I'll be sure to let it out on the motorway a bit more regularly.