Hi all, recently had my glow plugs changed locally at a reputable garage.

 

However, I have now noticed my MPG has dropped c.10% with no change to my driving style or weekly journeys. Is this a pure coincidence or could there be a link?

 

Car is a 2016 4x4 DSG estate, 190tdi. Average dropped to around 41mpg mixed driving. However, my normal 140 mile round trip to Sheffield used to give around 52mpg on the computer, but now around 46 mpg.

 

Any guidance much appreciated 👍

Has the mpg dropped due to a change in the weather?  A colder spell would, of course, give longer warming up times.  Or maybe it's the winter diesel fuel?  Are you using the same fuel from the same garage?

Winter spec Diesel from late October til March does not mean worse economy if the temperatures / weather in December is the same as it was in September.

 

But shorter days, colder weather and longer to get up to temperature with more stuff on might well affect fuel consumption.

But then on runs turbos love cooler / denser air, and if you have summer tyres still on then there is cooler road surfaces and less grip / traction / friction.

Swings and roundabouts. 

 

@smithymartynWere you running your car last winter and is the economy worse than last November til March?

 

 

Thanks all. Same fuel as normal and also same period last year was better than now i.e. same as pre Glow plug change 

 

Has someone changed the units from UK gallons to US gallons?  The UK gallon is 160 fluid ounces, compared to 133.23 for the US gallon, which would give about a 17% fall in mpg.

Is the coolant temperature & oil temperature working as normal? 

 

Glow plugs obviously help with starting when cold but will also run while the engine is warming up for a short time after starting.

 

I find it difficult to understand how they could impact fuel economy so much.

It would be more likely something else was disturbed during the change.

 

 

Why were they changed in the first place? 

What is your "tank to tank" economy and has it really change? 

You could just have been unlucky that the last trip you recorded included a regen?

 

It would be better to monitor over a tank or two as long as you don't have any warning lights.

Thanks all.

 

Will do some tank to tank calculations and ignore the computer for a bit.

 

As an aside, yesterday am (damp and 5 degrees) the car took a bit to start. Didn't feel like it was the battery, more like the problems I had before when I had a warning light for glow plugs. No warning lights at present, although I have Carista, so may plug in and have a nosey.

What temperature was it with your delayed start? 

On my Octavia TDI I had a few years where I thought there was a software problem because the engine would take 2-10s to start on occasions.

 

My battery eventually died & after replacing it, there's been no problems starting since.

 

Did you have problems with the glow plugs that lead you to change them or just poor starting performance? 

Very interesting thread...

 

I was about to post re: worsended MPG after...New Tyres..!!!

 

Replaced the tyres in June '23 with exatcly same type (Scorpion Verde 19"), and noticed MPG worsened from mid-40s to mid-30s. I've checked pressures, air intake, usualy things without dismantling the thing...all to no avail. Even threw a couple of bottles of 'diesel injector cleaner' through it just in case some weired magic occured...

 

I'll check the unit settings, but I did the fill the tank and calculate against mileage and it still came out at mid-30s.

 

Any ideas from anyone?

 

Should I consider a re-map?

On 27/12/2023 at 08:34, smithymartyn said:

Hi all, recently had my glow plugs changed locally at a reputable garage.

 

However, I have now noticed my MPG has dropped c.10% with no change to my driving style or weekly journeys. Is this a pure coincidence or could there be a link?

 

Car is a 2016 4x4 DSG estate, 190tdi. Average dropped to around 41mpg mixed driving. However, my normal 140 mile round trip to Sheffield used to give around 52mpg on the computer, but now around 46 mpg.

 

Any guidance much appreciated 👍

@smithymartynDid you get this resolved in the end?

Hi mate, still tracking but did notice a reasonable increase to early 50'slast week on a 70 mile run. Put some redex in too, so will report back when refilling. However, the other evening after the car had stood all day (post a 6am -7 degree start) it took a good while to turnover. I still think when plugs were changed something else got screwed up? Could anything have happened to timing? Cheers

 

Could the glow plugs not have been installed properly causing a loss of compression in ones of the cylinders? 

 

Do you see anything if you remove the engine cover? 

 

Is not uncommon to have an occasional poor tank of diesel from a garage or a badly timed regen which causes multiple heatups without reaching the target temperature for long enough.

 

Dont forget the change to winter or summer spec fuel which the engine needs to adapt to.