Towing with DPF equiped VAG car

[mark wade]

Hi all,


I have a question for those that are 'in the know'. I tow a caravan with my 2007 Golf TDi 170, it is equiped with a DPF and 'touch wood' all is well. Due to the cost of a replacement DPF I am constantly trying to give it an easier life as possible whilst towing. My question is, at cruising speed of 60mph is it better to leave the car in 5th gear @ 2000 revs which roughly coresponds to max torque or use 6th gear @ approx 1600 revs, still pulls OK on a flat surface but below max torque. I have used both gears on a flat stretch of road with the cruise control engaged and there is very little difference in fuel economy. What I would like to know is which gear will give the DPF an easier time regarding higher DPF temperature (which is good) verses higher soot production (which is bad) All info will be greatfully received.

Mark.

PS I have also posted this thread on other model related forums which might contain more traditional towcars.

[richard@thebrae]

For me, 5th gear @2000 rpm should give a higher temp (good) a higher gas flow with very little diff. in particle content (good) than it labouring ever so slightly in 6th.
I towed a 1300kg van with my 2008 Golf 1.9 105 7 speed DSG. It towed surprisingly well and even used 7th on the flat. 5th seem to tackle any incline on the M/way ect.
One experience I had was when while towing up a sharp steep incline from a base of 30mph I gave it some throttle in 3rd and the exhaust gas pressure sensor failed. I do not know if it was related to me gunning it under load or not, or maybe it was just coincidence. From new, I always used Shell V power to try and avoid sooting up things and from the exhaust appearance at 38k it seems to keep the exhaust system a little cleaner

[martin1810]

It should't matter how you drive because the ecu should adapt dpf regen to the current ecu monitored conditions. In terms of general low soot build up you need to drive at max speed with lowest throttle input. i.e keep it lean. That's why motorway driven cars have less dpf problems. All of this is impossible to accurately quantify because you don't control the fueling, the ecu does.

[mark wade]

Thank you very much for the replies. There lies the problem! two replies and two differing opinions. I can see the logic of both replies, hence the original post. Seems that using fuel with a low sulphur content might help as well but I need to do more research on that.

Mark.

[c.grex]

Id get on with your journey and look forward to relaxing in the caravan when you get there! I'd only worry about a DPF issues if your just doing short nipping round town runs, and in that case why buy a deisel.

you don't seem to be nipping anywhere, I'd not worry and enjoy the drive!

[Alan02]

You should be fine in 6th. The ecu will decide when to do a re-gen, and in most cases you wont know its being carried out. It post-injects extra fuel after tdc which gets dragged into dpf and raises temp. to burn off the soot.

[richard@thebrae]

Thank you very much for the replies. There lies the problem! two replies and two differing opinions. I can see the logic of both replies, hence the original post. Seems that using fuel with a low sulphur content might help as well but I need to do more research on that.

Mark.
Hi Mark,
I think that martin1810 and my self were saying the same thing just put differently.
I am sure you have seen a diesel working hard and the exhaust fumes coming out black.
I would say that the ecu would determine a lighter injection quantity if the engine is pulling easily, the burn would then be more complete, hotter and cleaner, and so the soot content of the gasses going through the DPF would be minimal.
I would say this will not leave as much soot deposits as lower engine revs in a higher gear for the same given load on the engine. (splitting hairs here)
In any case it is the ash content that is left after a regeneration that is the killer of DPF's.
We all know that short journeys is not good for diesels with DPF's as the temp does not get high enough to give a clean burn in the engine and so the soot builds up and regeneration of the DPF cannot occur untill a forced one is induced or a 30 min. blast up the M/Way is done to give the ecu the chance to make it happen.
As for V-Power it is not strictly 100% from oil like standard diesel. it is Gas to Liquid Tecnology mainly, with some bio and other additives. (bio content is determined by legislation)
and so the dirty content is much less and so there is less soot also.

[mark wade]

Thank you very much for the continuing replies, they make very interesting reading. I have to say that I hadn't thought about the engine management weakening off the fueling as far as poss whilst cruising, make perfect sense when you think about it though. Cheers.


Mark.

[philipharmes]

Youv'e got to think of a diesel engine as an air pump. There is no throttle as in a petrol engine, so it will pull through all the air it can get. That air is roughly ambient temperature raised slightly by the turbo/intercooler. This air has a cooling effect on the engine & exhaust gas. Therefore the higher the revs the cooler the exhaust gas will be. Lower revs will therefore give the highest exhaust temperature given the same power demand on the engine.
DPF's regenerate either passively or with assistance from the ECU by injecting extra fuel. Your DPF will be happily regenerating passively while towing as the engine is working quite hard.

[mark wade]

Thanks again for the replies, I sent the same original post to VW to see what their take on it was. Here is their reply.

From...Volkswagen UK Customer ServicesTo...Mr Mark WadeSubject PF driving style recommendations
Reference: VW-2013/09-033370

Dear Mr Wade

Thank you for your recent enquiry regarding caravan towing and the diesel particulate filter in your Golf.

I have spoken with our Technical Support Team who have provided the following advice: we would predominantly recommend the use
of 5th gear and only use 6th when on the dead flat with no load.

Should the DPF light illuminate on the instrument cluster the recommendation is to maintain a vehicle speed of at least 40 mph
and an engine speed of around 2000 rpm for at least 10 - 15 minutes to successfully perform a DPF regeneration.

I hope this information proves useful. If we can be of any further assistance, please do not hesitate to contact us on the
number below.

So there we have it, pretty much how I have been drivng anyway. It also seems that using Shell V power or BP Opimax fuel can help the engine produce less soot but probably at extra cost.