Hyundai i40 1.7 CRDI - poor MPG after oil change

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Wed 22 Jul 2015 19:21
Hyundai i40 1.7 CRDI - poor MPG after oil change - TopScot

2 weeks ago I done a service on my i40 and after the oil change my average mpg has dropped from 55mpg to as little as 38mpg and on the motorway when I was regularly getting as much as 70mpg the car is bairly hitting 60.

I have used the correct oil for my i40 (shell helix c3 5w-30 fully synthetic) After a week of poor MPG I thought perhaps the oil might have been faulty. Off I went to a different supplier for the same oil and still getting poor MPG. Any pointers would be appreciated.

Many thanks in advance.

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Wed 22 Jul 2015 21:58
Hyundai i40 1.7 CRDI - poor MPG after oil change - Peter.N.

Its unlikely that an oil change will have much if any effect on the mpg, its more likely that something happened when the oil change was being done. Check for disconnected wires/pipes.

If you can't find anything take it to a diesel specialist and get the fault codes read.

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Wed 22 Jul 2015 22:12
Hyundai i40 1.7 CRDI - poor MPG after oil change - TopScot

Thanks you. I checked all wires and pipes, amd for any leaks. Also blasted it on the motorway incase the DPF was trying to generate. These i40 are actually very oil sensitive when it comes to MPG. When I took my first i40 to a local garage for a service I had this same problem and the oil he used all though suitable was cheep and nasty and unchanged it immediately to my usual and got normal results.

this is the first service I have done on my new one since I bought it. I've carried out all the usual checks and can't see anything wrong

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Thu 23 Jul 2015 10:59
Hyundai i40 1.7 CRDI - poor MPG after oil change - Peter.N.

Never heard of that. What effect does using the wrong oil have on the engine?

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Thu 23 Jul 2015 11:10
Hyundai i40 1.7 CRDI - poor MPG after oil change - elekie&a/c doctor

If you have used the correct spec oil,I really cant see how fuel consumption can be affected.If you still have the old oil,why don't you re-use it to confirm your thoughts??

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Thu 23 Jul 2015 13:06
Hyundai i40 1.7 CRDI - poor MPG after oil change - TopScot

I can't understand it either. However Im not alone on this, It's well documented by other owners on the i40 owners website. As for the old oil it's at the dump for recycling!

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Thu 23 Jul 2015 20:33
Hyundai i40 1.7 CRDI - poor MPG after oil change - RT

Never heard of that. What effect does using the wrong oil have on the engine?

The wrong viscosity can cause increased internal drag as well as affecting hydraulic tappets/lash adjusters which can alter valve timing enough to affect mpg.

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