Coolant fans staying on

[Chris90]

Hi all

I have a 2.0 TDI 175bhp B8.5. 2012 plate.

Tonight once I got home from work (25miles or so, 40mins, air temp ~1.5c) that the coolant fans kicked in soon as I pulled up on drive and switched car off. Havent noticed this before, but know some cars do it if things are a bit warm when just stopping. Kept on going for 2 minutes, had a look round in engine bay to see if anything untoward etc. nothing. Hopped back in and fired it back up, coolant temp was around 50-60c, but quickly got back up to 90c.

Turned it off again and they kicked back in immediately. Stood around a minute expecting them to go off and nope. Waited a good 6-8minutes before they eventually powered back down. By that time, had another look under the bonnet and a feel of the pipes expecting them to be hot. All coolant pipes were nice and warm to the touch, and could even dip finger in the coolant it was that cold.

Anyone elses car done this? Just find it a bit strange in the middle of a cold night and doing it twice. Havent had time to stick it on the computer yet for any codes as its 2.45am.

Chris

 

[gary_a4_quattro]

Car was probably mid way through dpf regeneration cycle when you turned it off, though little surprising taking account of the journey the car had just been on.

My 3.0 tdi does this occasionally, especially if it hasn't had the opportunity for a 'good run' for a couple of weeks ( this is accompanied by an increase in idle to c. 800 rpm and a slight 'warm engine' smell - tho coolant temperatures normal )

Have a read of post #7 on this thread on A5OC , some useful info.

Hope that's what it is and nothing more involved ?

 

[feva]

Mine does this Chris, as mentioned above probably dpf cycle.

Sent from my Note 4 using tapatalk

 

[Zafi]

Next time listen at the exhaust, you can hear it doing a regen.

 

[Chris90]

Interesting. Never thought of a regen. No lights on the dash to indicate it was happening. Car does about 450miles every week and a half and gets given the boot every now and again to blow the cobwebs out.

What are the signs of a regen?

 

[Chris90]

What measuring blocks can I check using vagcom?

Odd one with mine is it only brings up advanced measuring blocks instead of the normal 3 blocks and 4 values in the basic measuring blocks.

NO idea what im looking for in terms of the DPF stuff either as this is my first diesel and car with DPF. be no issues if it was a 1.8T haha

 

[desertstorm]

The B8 with EDC17 ECU's will give you the Advanced measuring blocks. It will pretty much be as described above the DPF regen was mid way through when you turned the car off. The DPF can be very hot at this point so the fans run till the temperature seen on the sensors drops to a reasonable level.
The number that is associated with the measuring block number seems to change across different ECU's so you need check what yours are. The DPF info comes together though in one block like this.

http://www.a5oc.com/forums/attachment.php?attachmentid=51481&d=1408362552
Time since last regen is in seconds and increments when the engine is running.

http://www.a5oc.com/forums/attachment.php?attachmentid=39785&d=1399647877

The ECU calculates how much soot is in the DPF as it knows the driving cycle that the cars been through and it measures the back pressure in the exhaust via the G450 sensor. You can see this as a measurement as exhaust pressure measurement. This graph shows roughly the values of soot at which regen occurs. I think you can do a forced regen upto 45 grams of soot. after that the car won't regen if the DPF is too blocked as it's liable to cause engine damage and also a potential fire risk.

http://www.a5oc.com/forums/a5-general-q/52313-dpf-soot-measurement-vcds.html

You can save measuring block groups on VCDS to use if you want to measure the same blocks on a weekly/ monthly basis say. That way you don't need to go finding all the blocks again.

http://www.ross-tech.com/vcds/tour/adv-meas-blocks.php

The G450 sensor is not that reliable and is quite often the cause of peoples issues with the DPF.

 

[Chris90]

Will have a drive to work in 4/5th gear at high 2000s rpm and hope it blows it out a bit by getting hot.

Can't say I noticed a rpm change at idle, but initially opening the door the first time it did smell warm, but couldn't pin point it when bonnet opened.

Can the values in vcds be obtained when ignition on or does car have to be up to temp and running?

 

[Chris90]

Update:

Managed to get the car plugged into VCDS today and checked the 6 blocks that were shown in the links DesertStorm posted up. Below is a pic of the values from my car at idle:

No other fault codes stored in the ECU for the engine.

From what I can make of the data....

Last regen was 11411 seconds ago. 190minutes or 3.1hours. Which works out right as last regen must have been on way home from work on Thursday night when the fans were active. Its 40minutes home from work on a clear run, and about 1 hour - 1hour 15mins on the way to work in traffic. Took me 1 hour to get home friday night so that puts us at the value there-abouts for the regen.

Oil ash volume: 0.04L. This works out to me 40ml of ash in the DPF. Car has done 35,000miles in its time. Not sure how this stacks up in the terms of DPF lifetime. But someone posted the limit is 175ml of ash before the DPF is dead. True?

Soot mass measured and calculated: 11.03g measured. 13.36g calculated. From looking at the graph of regen types and their soot levels, I fall within the passive regeneration stage, which is below 18g of load in grams (presuming that the scales im comparing is right here). It could well have been that the DPF tipped into the active regen stage which would have caused the fans to remain running. A sucessful regen when I drove to work at 70mph in 4th gear ~2800 to 3000rpm (along with a bit play with a ST) would have made the levels drop.

163,965m since last regen. Works out at around 100miles. Its a 50mile round trip to work each day. 50miles on the thursday and 50miles on the Friday. Works out spot on with time of regen.

Fuel consumption aint really a huge player but 12L is 2.6gallons and at 38mpg thats 98.8miles. Again, near enough spot on with the rest of the data.


So, my review of findings is above. Can anyone confirm with what ive stated as being right in terms of DPF statistics and whether, more importantly, the values of the data shown are acceptable and nothing to worry about.

Thanks

Chris

 

[desertstorm]

They are good Chris. The oil ash volume I believe just a figure based on the mileage of the car. This is why you need to use the correct oil with DPF's low SAP's which doesn't cause as much ash if it finds it's way into the DPF.
The DPF will do it's own passive regen if it gets hot enough in use and that usually come from longer high speed trips that you appear to be doing.
The other reading that will tell you about the state of the DPF is the exhaust pressure. This is what the ECU uses to calculate the soot loading as well as the useage of the car.

 

[Chris90]

Sweet, pretty much as I expected then.
Use the stuff from the dealers for the car as cheap as chips from TPS. Sure its the low ash one as it says on the front of the bottle.

Whats the other measuring block for the exhaust pressure? There was a couple listed under the particle filter but these shows 0-hpa and think the other was 7 or 8 hpa.