My VW Ameo diesel fuel efficiency drops after service: Why?

Facing a mileage drop from 17 km/l to just 12 km/l during my city drives.

BHPian AdhirajVW recently shared this with other enthusiasts.

Hello BHPians!

My humble VW Ameo 1.5TDI just reached 60,000 km a few months back and for the first time I decided to get it serviced from outside and not the ASS because of the following reasons:

1. Can see the work being done in front of me
2. Can afford a much better quality of Engine Oil at a lesser service cost.

However, after the service, I witnessed a drop in mileage in the vehicle. I thought of giving it some time for it to improve but after 2 months and 3,000 km, it is still the same. When I say drop I mean the following:

1. Highway: My car used to give around 24-25 km/l on highways, which had dropped to 19-21 now
2. City: Inside the city used to be around 15-17 km/l which has dropped to 10-12 now.

I got the below work done:

• Engine Oil Change: Used Rowe 5W-40. Flushed with AMSOIL before filling the new oil.
• Oil Filter: Changed with OEM one
• Fuel Filter: Not changed
• Air Filter: Since I got a new BMC filter installed at around 50k km, just got it cleaned with compressed air.
• Rear Brakes: Got the drum and pads replaced
• Cabin Filter: Changed with OEM one

One difference which I noticed was that the VW service centre filled the engine oil till midway of the min and max mark and now the engine oil is at the max mark (not more).

Can someone help in identifying the reason for the drop? I am concerned if my engine is not getting damaged internally.

Here's what BHPian vishy76 had to say on the matter:

I would recommend getting the fuel filter changed as well. It's not a good habit to prolong fuel filter changes on a diesel here in India since diesel quality, in general, is patchy. Anything beyond the 15K km mark is stretching it. Contaminants in the fuel can be detrimental to the life of expensive ancillaries such as the high-pressure fuel pump and especially the injectors.

Secondly, check the MAF sensor. Since you are running an aftermarket air filter that is cleaned using oil, it might have caused the MAF to get clogged. If the engine thinks the air entering the intake is less, it will automatically increase fuel to compensate. Cleaning the MAF sensor isn't all that difficult either.

Lastly, if the majority of the mileage you have clocked has been in the city or has included short trips, it's advisable to get the intake manifold, anti shudder valve (throttle body) and the EGR system (EGR valve, cooler, return pipe) cleaned up thoroughly. I have noticed this improves fuel economy quite a bit. This is a labour-intensive task, so better to keep it for the end.

Based on what I have read, the 505 01 specs of oil had originally been prescribed by VW for the PD engines where the high-pressure pump is driven by a lobe on the camshaft. This spec of oil was prescribed to offer extra protection to that lobe. I know several TDIs running 505 00 and not having any issues wrt fuel economy or longevity.

The recommendation for the TDIs is 5W40 fully synthetic oil.

Here's what BHPian Rohit Tripathi had to say on the matter:

Hi Adhiraj,

I have a 2015 TDI Vento and sharing my view. I think the fuel filter should be changed as this will impact your injectors. Tyre alignment, pressure, oil ratings should be as per VW specs.

I recently travelled to Pune and Hyderabad in Nov and one of the injectors failed near Belgaum. Before this while, there was no drop in performance but after replacing the injector in Belgaum the mileage went up from 21 to 24. I use 15 inch 205 Yokohama s drives.

Hope this is useful.

Here's what BHPian JoshMachine had to say on the matter:

As others have quoted, replacing your fuel filter, in a diesel car, is the first thing that you should do.

I too drive a VW 1.5 TDi car and have to strictly adhere to the replacement regime every 10k km or so.

Besides straining the 'fuel line' due to inefficient capture of the dirt and dust, a faulty fuel filter (that is not replaced for quite some time) will also wear the fuel pump and injectors.

The obvious effect that you see will be reduced/sluggish engine power and reduced fuel efficiency.

Here's what BHPian humyum had to say on the matter:

Just a hunch. After a 10-15 kilometre drive, can you touch just the part outside the alloys/steel rims from the centre and see if all of them are hot uniformly. Just peck it, it might be very hot but check if it's uniform.

This is to rule out a sticky brake pad/lining

Secondly, is 5W40 the recommended grade for your car? Or is it 5W30? If the grade was changed from 30 to 40, the economy will take a hit but not to the extent you have mentioned.

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