Problem with fuel mileage plummeting on diesel Zafira.
Discussion
Firstly, sorry if this is in the wrong place... new here and this looked about right. 
My wife and I purchased our 2nd Vauxhall Zafira in March 2018. Our previous petrol one was getting old, but we liked the car and it suited our needs. As we're self employed we have to keep mileage records, and that car used to give is about 33mpg. The new one, when we got it, was on the same, 33.2mpg IIRC.
Within 2 months we'd got that to 42mpg, and it slowly kept rising. It topped out at 43.8mpg. We had absolutely no idea how someone was driving this car and only getting 33mpg out of it. It's a really nice drive. Needless to say we were happy as we were getting a lot more bang for our buck so to speak. At first I assumed the board computer was wrong, so I manually recorded the odometer and fuel and worked it out... It was accurate to about 2%. Close enough for me!
For the last few months the mpg has been dropping. When it dropped well below 40mpg I reset the 2nd board computer to monitor it. Although the first board computer is reading 38.7mpg on the last 123 gallons, the 2nd board computer is saying we've done 32.7mpg on the last 27gallons. And I've worked out the last 4 gallons myself and it's accurate.
So whatever was happening is happening again. Problem is we have no idea what it is. We've spoken to a couple of mechanics and the only advice we've been given is "use the premium deisel" and also "try Red-Ex" neither of which have made one jot of difference.
The car drives absolutely fine, but it does have one new oddity. When I'm sat at lights, car stationary but the engine is ticking over, the "instance consumption" usually says 0.1 gal/h. Maybe 0.2 gal/h. Occasionally this jumps up to anything like 0.7, 0.8, 0.9 gal/h. Yet I'm sat there, stationary, the engine sounds fine and the revs are sat nicely at 900 or so. When it does this, if so watch the fuel, I can be doing 25mph in 3rd gear, getting 15 miles per gallon. Only a restart of the engine will fix it.
The car was serviced and passed it's MoT last March, zero issues. Reg is DK63 AFK is anyone needs to look up specs (I wouldn't know what you'd need to know)
Does anyone have any ideas at to what's wrong? Cos I'm baffled.
My wife and I purchased our 2nd Vauxhall Zafira in March 2018. Our previous petrol one was getting old, but we liked the car and it suited our needs. As we're self employed we have to keep mileage records, and that car used to give is about 33mpg. The new one, when we got it, was on the same, 33.2mpg IIRC.
Within 2 months we'd got that to 42mpg, and it slowly kept rising. It topped out at 43.8mpg. We had absolutely no idea how someone was driving this car and only getting 33mpg out of it. It's a really nice drive. Needless to say we were happy as we were getting a lot more bang for our buck so to speak. At first I assumed the board computer was wrong, so I manually recorded the odometer and fuel and worked it out... It was accurate to about 2%. Close enough for me!
For the last few months the mpg has been dropping. When it dropped well below 40mpg I reset the 2nd board computer to monitor it. Although the first board computer is reading 38.7mpg on the last 123 gallons, the 2nd board computer is saying we've done 32.7mpg on the last 27gallons. And I've worked out the last 4 gallons myself and it's accurate.
So whatever was happening is happening again. Problem is we have no idea what it is. We've spoken to a couple of mechanics and the only advice we've been given is "use the premium deisel" and also "try Red-Ex" neither of which have made one jot of difference.
The car drives absolutely fine, but it does have one new oddity. When I'm sat at lights, car stationary but the engine is ticking over, the "instance consumption" usually says 0.1 gal/h. Maybe 0.2 gal/h. Occasionally this jumps up to anything like 0.7, 0.8, 0.9 gal/h. Yet I'm sat there, stationary, the engine sounds fine and the revs are sat nicely at 900 or so. When it does this, if so watch the fuel, I can be doing 25mph in 3rd gear, getting 15 miles per gallon. Only a restart of the engine will fix it.
The car was serviced and passed it's MoT last March, zero issues. Reg is DK63 AFK is anyone needs to look up specs (I wouldn't know what you'd need to know)
Does anyone have any ideas at to what's wrong? Cos I'm baffled.
Lutzie said:
Sorry, I don't know what DPF regens are?
Google is your friend, but the short version is that the ECU puts excess fuel into the engine so that the exhaust runs extra hot and burns up the soot accumulated in the diesel particulate filter. You would probably know when it was happening if you knew what to look for. It shouldn't happen very often if everything is working properly, but if it's failing and keeps getting retried then I suppose it might use enough fuel to affect your consumption figures.I presume you don't have any tyre pressure issues ??
I only mention it as a friend once bought a car identical to the one he just sold and it was over 10 mpg less economical. Turned out to be low tyre pressures that were not immediately noticeable.
Doesn't really sound like your issue but just thought I'd mention it.
I only mention it as a friend once bought a car identical to the one he just sold and it was over 10 mpg less economical. Turned out to be low tyre pressures that were not immediately noticeable.
Doesn't really sound like your issue but just thought I'd mention it.
Sounds like a constipated DPF. My mum and dad's Astra was completed buggered as a result of a faulty DPF which led to a coked up inlet manifold long before it had reached it's tenth birthday and 65,000 miles (the latter being a clue to the state of the engine). Even the main dealer couldn't stop it breaking down, I got my mum home after it died completely by disconnecting the exhaust behind the turbo.
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