BEZ101

Good morning,

Hoping someone else has previously had and rectified the economy issues I am having.

Bought an E61 525d auto a few months back, 96,000m, FSH. Really pleased with it but cannot get it to deliver more than 27mpg average... Even on a run.

So far I have done the following, not all fuel related but worthy of note : DPF delete (removed brick and also in software), EGR delete (software), swirl flap delete (software), remap. It was running at 60-70degC so I tested and replaced EGR thermostat (which was indeed stuck open), this got my temps upto around 80... So I changed the main thermostat, which after bench testing, looks to be working reasonably well but not perfect (tested tonight and it opened at 80 and closed at 75(stamped at 88)). The new thermostat has made it worse as it now runs between 75 and 80 and takes a good while to get there.

Any ideas on what else could cause bad fuel economy? I was considering having my injectors tested but I'm reluctant as it runs smoothly; I would have expected lumpyness on tick over.

Many thanks in advance,
Cheers,
Phil

sanjsanj

Temps of 75-80C are most definitely the culprit. Did you get the thermostats from BMW? the ones from ECP fail within a few miles. Also, there's a third thermostat in the gearbox oil cooler, that's probably failed and is quite expensive to replace.

You should try this out: 535d The Extra Thermostat fitting Guide. - E60/E61 2004-2010 - BMW 5 Series Owners Board

let us know how you get on!

BEZ101

Thanks for the advice. I was not aware of the third thermostat.
Both replacement stats were Ebay jobbies so probably not the best quality.

I like the fix in the link you sent. Might have a stab at that.

I will update with results.

BEZ101

Hello,

Just wanted to update.
I bought a Renault 5 thermostat and fitted in series with the return pipe and car now gets up to 90DegC rather quickly. It then alternates between 90 and 83 and I can only assume this is the effect of the grille shutters opening and shutting but I am unable to confirm without setting my Go-pro up and going for a bimble.
I will update again if my fuel economy issues go away.

Also I spunked £96 having my injectors tested to find that they were all fine and within manufacturer tolerance.

Many thanks,
Phil