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-   -   Diesel thermostat definative answer (https://www.the75andztclub.co.uk/forum/showthread.php?t=68468)

Matt1960 10th September 2010 09:21

Thanks Jules,
But I have changed maf sensor, intercooler rings, filters, pcv, egr clean, etc. to try to improve matters. I can get 40mpg at 60mph on a motorway, but nowhere near 50mpg.
I also drive with a fairly light foot, and my area is not hilly.
Yet to test the injectors for leakback, so this may be an option. But I did try injector cleaner.
Matt

Jules 10th September 2010 10:46

Mmm yes you must have less hair than me now Matt!
The performance and economy varied widely even when they were new.

Some were lively, and others were sluggish.
However recently we cured a very sluggish ZT 131 with 50K miles on it.

After much deliberation I advised the owner to go for a punt & to re purchase the XPart 131 remap CD for his VIN number.
We programmed it in and guess what ...............CURED ...like new again.


So it seems either it wasn't mapped properly from new

Or

The mapping had somehow in it's life got corrupted.
I suspect theres a few similar owners Cars driving around with the same Mapping problems

BarryH 10th September 2010 11:50

Quote:

Originally Posted by Matt1960 (Post 586029)
Thanks Jules,
But I have changed maf sensor, intercooler rings, filters, pcv, egr clean, etc. to try to improve matters. I can get 40mpg at 60mph on a motorway, but nowhere near 50mpg.
I also drive with a fairly light foot, and my area is not hilly.
Yet to test the injectors for leakback, so this may be an option. But I did try injector cleaner.
Matt

Hi Matt,I improved my mpg from 39 to 44 by having a full service,changing discs and pads all round(needed doing anyway) and renewing the maf sensor.I live in a rural area which is quite hilly and although I can`t get up to 60mph very often I am very pleased with 44mpg.Would love to take the car on a long run to see if I can improve on 44 but not possible at this time.In my opinion changing the stat won`t make any difference to mpg.
Regards
Barry:}

Jules 10th September 2010 12:04

Matt has already changed his Stat!
Most members DO report an MPG improvement (some more than others)

I have a list of Affidavits from very happy owners somewhere if anyone wants me to list them?

Matt1960 10th September 2010 12:33

Thanks again Jules,
I Dont know whether my performance is down or not. It certainly improved when I replaced the MAF sensor below 2000rpm. And I am not intersted in performance too much anyway. But improving mpg to somewhere near 40mpg would be great.
I am certaibly not saying replacing the stat did not help, but maybe 1-2mpg, so for me, hardly noticable. However the benefits with regard heat in the cab were well worth it, till I retro-fitted a new FBH this year, which made that benefit slightly redundant.
I would consider a punt with a mapping disc, as I think they are about 200 plus vat, but once I found a T4 (now ems has gone) the total cost would be near 300. Thats a lot of money to get back at 8000 miles per year.
But I will continue to search for the answer, if my car is much more uneconomical than other CDTI autos.
Matt

James.uk 10th September 2010 12:49

Ellow Jules.. I haven't had mine remapped but I have got a very nice Garmin 200w sat nav, will using that help the cars MPG any? :D

(Plzz Note:- i didn't mention biscuits).. :D

Matt.. I ave around 32 mpg locally, and the car did managed 46mpg over a 1000 mile trip when on loan to a lady friend for her annual hol touring down South. But the best I can get, even on long mway runs is around the low 40's.. But, in the cars defence, I do tend to push on a bit especially on long mway runs.. :o
...

Matt1960 10th September 2010 12:52

Quote:

Originally Posted by James.uk (Post 586085)
Ellow Jules.. I haven't had mine remapped but I have got a very nice Garmin 200w sat nav, will using that help the cars MPG any? :D

(Plzz Note:- i didn't mention biscuits).. :D

Matt.. I ave around 32 mpg locally, and the car did managed 46mpg over a 1000 mile trip when on loan to a lady friend for her annual hol touring down South. But the best I can get, even on long mway runs is around the low 40's.. But, in the cars defence, I do tend to push on a bit especially on long mway runs.. :o
...


James, but of course not more than the legal speed limit:(
Matt

T-Cut 10th September 2010 14:55

IMO the BMW comment that a different (higher temp) stat will not achieve anything is contrary to observation. There are lots of people around the forum who had cool running diesels which were transformed (temp and MPG-wise) by renewing the stat. That in itself is disproves to the comment. I would also argue that the engine yields insufficient heat to raise the temp much higher. For example. if you were to restrict the flow through the thermostat, or even blank it off, do you think the engine would reach 100C and more? Try it and find out. I think the apparently redundant radiator fan would be woken up!

It may well be so that the cooling system in the diesel is simply too effective. There's a rather large volume of coolant circulating in a large cooling system. Maybe the use of a smaller radiator would be a better approach than partially blanking off the standard one?

TC

crashmarks 10th September 2010 15:18

I think your right T-cut the engine is overcooled. i suppose looking at it from their point of view they need to be sure that it can comfortably cool the enging in the most extreme circumstances i.e towing a full weight trailer uphill through the sahara desert. not much good to us though driving one up round our home towns.

T-Cut 10th September 2010 16:07

Agreed, but using the same radiator matrix for the diesel, V6 and K16 seems more like cost saving than engineering. IMO, the diesel is markedly over-cooled under 'normal' running conditions.

TC


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