What was the reason why 9M-MRO burned more fuel on one engine? MH370 Factual Information reported "Right engine consumes average 1.5T more fuel per/hour compared to left engine" on p.28 (page 47 on page count)

http://mh370.mot.gov.my/download/FactualInformation.pdf

Looking at spotters photos on the web I spotted the following difference:

Some kind of visible replacement (partial or total) to the left engine was made after Oct 28 '13 and before Jan 22 '14. 

Before - Two shades, longer curving, bigger bulge on top engine border before exhaust.

After - One shade, steeper curving, smaller bulge on top engine border before exhaust.

Google Drive document with links to 9M-MRO photos (I can't post more than 2 links since not enough reputation still)

https://docs.google.com/document/d/1tkY6H8zQmOyJj0M2_gd_j81iDr2MeumBoIlrYNtbcus/edit?usp=sharing
Those engines all look the same to me.

1.5T per/hour difference does seem excessive, but probably not unheard of.  It could be just because one engine is newer than the other and has less wear on it.

If you look at APPENDIX 1.6B of that same report it shows that the right engine consumed about 1.5% more fuel during Takeoff and Climb, not 1.5T more, so it may just be a typo. 

(APPENDIX 1.6B WF is fuel flow in lbs/hr)




Here are some crops of the photos you linked to:


Jan. 15, 2012 




Feb. 16, 2013




Oct. 28,2013




Jan. 22, 2014




Feb. 8, 2014




Feb. 10, 2014