Ozbargainers, I'd like your opinions please. Background info: I own a 2006 Mitsubishi Lancer 2.0L Sedan, currently sitting at around 187,000km. On a fuel-up of ~38-40L, I could usually average between 500-550km.
On 11/2, I took my car in to my local mechanic for a minor service, and got the timing belt changed on 13/2. Between those 2 days, I barely drove the car. Immediately after getting the timing belt changed, I noticed an increase in the fuel consumption of my car, but thought it was perhaps an error in the fuel consumption gauge (like what happens when the car starts/ends on a hill and gives a false reading). I went overseas between 18-27/2, and the car was left idle in the driveway of my home during that period. Once I arrived home, I drove to and from work as usual, and noticed that there was a definite change in how many km I could go over a full tank (~300km from a full tank).
I took the car in to the mechanic on 1/3, and the guy looked around in the bonnet of the car and did some computer scan, and all came back clear. I mentioned that the fuel consumption had increased post-timing belt change, but he refused to check out the timing belt "because it would take a whole day and I don't have time for that". He then told me to monitor fuel economy over the next 2 full tanks. I did so and recorded 361km on 38L, followed by 420km on 37L. I took these figures (with photos) to the mechanic and he said he had no idea what could be wrong with the car, and that he couldn't help me (and still refused to check the timing belt). He put it down to erratic driving behaviours or bad batches of fuel. FYI my driving behaviours have not changed, nor are they erratic. I fueled up all 3 times at my local Woollies Caltex with 91ULP.
My question: is this normal after getting the timing belt changed?? I'm currently monitoring how far my car goes on the 4th full tank, since there was a big increase between the 2nd-3rd tanks.
TLDR: got timing belt changed, noticed significant decrease in fuel economy. Fuel economy improved over 3 full tanks, but is not yet what it used to be. Is this normal vehicle behaviour after getting the timing belt changed, or should I get a second opinion?
Edit: Unsure if any of this information is relevant, but.. The mechanic and my dad have a longstanding good relationship. The mechanic has previously stated that my car runs surprisingly well compared to other vehicles of a similar make/model/year. When picking my car up after getting the timing belt changed, the mechanic said that my car strangely had 2 timing belts and some hydraulic tension thing (sorry, unsure exactly what it was due to poor memory), and I paid around $450 for the parts + labour (this was separate to the service). Could be chinese whispers, but I have also heard recently from my mum, who works with a lady whose husband is a mechanic at a dealership, that he gets frequent calls from my mechanic with questions on what to do as he is apparently clueless.
It's a pretty big job to replace timing belt. I wonder if all the sensor connectors were put back in place correctly. Normally check engine light would come on though.