Startling MPG

[DMK]

As I use my E30 318 touring all year round as both my everyday car and for my business traveling all over the country, I need total reliability. When it recently developed a very slight misfire noticeable only at tickover (that turned to be complete absence of ignition in one cylinder which was slightly down on compression), I decided to bite the bullet and go for a complete engine rebuild - it had already had a new cam fitted only 10,000 miles previously and the engine was just coming up to 150,000 miles.

Since the rebuild (carried out by a local engine man who specializes in BMW engine rebuilds) I have put another 3000 miles on the clock of mixed driving all over the country - high speed motorway work, rural A/B roads, country lanes, urban traffic jams....

I always record my fuel consumption and mileage every time I refill her. Pre-rebuild I got a consistent 34-35mpg and joked with my wife, it didn't matter how I drove, it always insisted on returning the same consumption. However post-rebuild, it is now returning an average of 54mpg with several runs hitting up to 65mpg!!! I thought I had got a figure wrong initially, but it keeps on returning the same.

The chap who did the rebuild said the engine was in good condition with very little wear but it was badly carboned up - which he reckons is always the case for these engines at 150,000 miles. I can't think of any other reason for such a dramatic change in the fuel consumption (but yes the injectors were also cleaned). Has anyone else has the same experience?

I had noticed it seemed to be going a long time between refills but 54+mpg on a '93 E30 318 touring?! At this rate I will have paid for the engine rebuild in a few months...

David.

[Speedtouch]

Good to hear, but it does sound a little far-fetched for a 1.8-litre petrol engine tugging 1.25 tonnes of German whip with the aerodynamics of a housebrick to be returning those figures.

I would expect mid 30s mpg average, with maybe 40mpg attainable on a long cruise.

[dan_lboro]

Manufacturing techniques and materials have improved over the years, so I guess if modern components (liners or pistons) were used on the engine rebuild then there may be less rolling resistance/friction in the engine? Or maybe the fuel is higher octane number? Or more likely the mileage odometer might not be working right or even a magic fuel tank? Its awesome that your getting those economies from a petrol, I struggle to get them with my e46 320d! I want that guy to rebuild my e30 engine!

[Cloggy Saint]

Modern diesels struggle to achieve 65mpg, I'd double check the maths!

[Doobit]

...or you've only been driving down hill since the rebuild!

[DMK]

Speedtouch, I admit I have fitted a new rear spoiler to improve the aerodynamics as the old one was starting to develop a hump in the middle, but I don't think I can put the improved fuel consumption down to that! As I said, pre the rebuild, it always returned mid 30s apart from the final fill with the misfire when it dropped to 26mpg. I was expecting the consumption to be identical or marginally worse due to a tight engine after the rebuild.

Dan_lboro may have touched on something as the rebuild included a rebore, new pistons, valves, and cam but even so an increase of 20mpg is going some. For the record I am still using the same bog standard unleaded petrol, the odometer accuracy is spot on (I navigate by expected mileage as predicted by the RAC between required road junctions when travelling to other parts of the country - Norfolk to South Wales and back a couple of weeks ago it was exact for the entire journey), and I subsequently discovered there was a weep from the fuel lines anyway.

As for double checking the maths, I work out the consumption every few thousand miles for all of the individual fills accumulated to date then average them out. This block covered pre and post rebuild and you can see the jump where I annotated the figures with engine rebuild, but I am happy to post my latest figures for anyone to pore over.

Perhaps I have just struck lucky over the past couple of months and always picked petrol pumps that were under recording the amounts of fuel dispensed. If anyone wants to queue up behind me, I am due for another refill soon

I don't expect my super economy to continue forever, but around 3000 miles thus far ain't bad. If anyone else has had the same effect, it would be nice to know how long it takes to wear off.

[tcos]

65mpg wow

[jmc330i]

65mpg wow

54mpg wow

[corkie]

[Speedtouch]

The phrase "Norfolk and Chance" springs to mind, given the OP's location and claims...