wickerman

Hello everyone after a few ideas. I get about 21/22mpg around town in my 2005 525d Auto sport E61. Goes upto around 30mpg on Motorways.
I have had the main Thermostat changed and the EGR thermostat and a new airfilter. The most i've ever seen the temperature go upto is 84c this was after about an hour on the motorway. Is this the best I will get from this car. I purchased about three months ago, but seriously considering selling it now I've spent the best part of £400 quid trying to sort out this poor MPG.

Someone mentioned on forums elsewhere the Gearbox exchanger ?

mmitev

84 C max after change of both thermostats is strange!
The only other ideas I have is to clean the EGR valve and the intake manifold.
And then to clean the DPF preventatively, as it may be almost blocked and increase the fuel consumption.
And maybe an error check of the engine, maybe something is wrong with it?
Not sure whether the MAF has something to do with fuel consumption.

Would be interested in other opinions and in your findings.

Theo

Check all pressure hoses, they tend to become brittle over time, especially relevant to an older diesel like yours. Depending on location and size these leaks have proven in the past that they can indeed affect both mileage and performance to varying degrees, sometimes both.

Temperature is still an issue though, should get another 5-8 degrees and most of all quicker, have you cleaned the EGR valve? I once saw a diesel (525d) that only reached proper temps after it was cleaned (heavy contamination). Could be that during the process the hoses were connected properly and weren't before but you might give it a try.

Stupid question maybe but I guess your mileage is stated in imperial mpg not US?

wickerman

Well not knowing that much about cars I went on to "www.bimmerforums.co.uk" to see if I could at appreciate and understand the issues.
After various discussions and checking the coolant temperature through the hidden menu and seeing that the temperature was never getting over 80c and the bad MPG I decided to ask the garage I purchased the car off to change the EGR valve which they eventually agreed to do!
But to be honest I wouldn't know where to look and know if they had changed it ? I also paid for another garage to change the main thermostat after more discussions on "www.bimmerforums.co.uk". I know they did change this as they handed me the Thermostat and the outer casing. They also ran a diagnostic check which came up okay. They also gave me a print out which states the engine was running at 90c. I suspect they let the engine run without actually driving it until it slowy went 90c. So i'm a bit confused on what to do next.

Thanks for the advise so far

Regards.

Wickerman.

mmitev

EGR valve is different from EGR thermostat.

Which one did they change?

wickerman

The garage I purchased the car from had changed the EGR and another garage I paid to change the Main thermostat.

Vista

That doesn't answer his question though, the EGR valve and EGR thermostat are different components (as is the main thermostat) The EGR thermostat can also impact your running temperature.

Theo

I hope you didn't do this because of my advice above, as the guys up here stated: EGR valve and thermostat are quite different parts. The EGR thermostat, as well as the main, is known to fail after some time and cause the car to run on a low temp and cause poor mileage. These would be your first points of attention when running with a low coolant temp.
The EGR valve is to my knowledge not as directly linked to temperature/mileage, however, I saw one case where cleaning one containing severe deposits did make a notable difference. As I said, might just have been a connection or hose that was reattached properly after cleaning and was loose before. I does never hurt to clean it though after such a long time in operation as yours.
Theoretically: if the EGR valve would be so contaminated that it would be stuck in a certain position I could see how this would cause poor mixture and therefore poor mileage. If stuck opened though it would cause a higher temp. in the engine though if I'm correct?

If you could verify what EGR related part they replaced we might be able to deduce part of the problem for you.

wickerman

Apologies. I believe it was the EGR Thermostat that had been replaced not the valve. Where is it located and is there anyway I could check it ?

AJH

Yes its on the front/top of the engine bolted to the egr. its black and cylindrical. it is held on with two bolts and a clip on the other end (linking to a hose). Undo the two bolts and the clip and then blow though one end, if you can it's fooked.