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Old 21-05-2010, 11:55   #1
slimtim
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Diesel engine running temperature.

MGZT CDI 135 2004 (facelift).
Ok I have run the diagnostics test as detailed elsewhere and my engine seems to run at a consistent 85/86 degrees c.
This is after a thourough warm up and hardly fluctuates if I am in traffic or coasting along at 50mph with the revs at approx 1600.
Even if I break the law and go up to 60mph (revs at 2000) it stays the same.


My question is, what is the optimun temp for a diesel engine in terms of performance and wear and tear?
These tests were done with an outside temp of about 22/23c.
Does mine sound about normal or a little low?
Tim
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Old 21-05-2010, 12:15   #2
DMGRS
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On the low side, but well within acceptable.
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Old 21-05-2010, 12:20   #3
slimtim
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On the low side, but well within acceptable.
Thanks!
Would you say low enough to suspect thermostat stuck in 'open' ?
Or am I looking for problems that are not there?
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Old 21-05-2010, 13:31   #4
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Sounds about right to me, checked mine on the way to Sheffield the other week and it was pretty much the same as yours. Think the thermostat opens at @ 88c, mine never went over 89c even when booting it.
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Old 21-05-2010, 13:33   #5
Styvy
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My advice m8 its good. idealy it should be 88-90ish. Unless you want to buy new thermostat and fit it yourself you can be stuck for at least 150. Leave it alone and enjoy. My thermostat change evolved into 200 for waterpump, 50 for thermostat and 200 for work.

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Old 21-05-2010, 14:29   #6
T-Cut
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The optimum running temperature for water cooled internal combustion engines is 95-100C. This is where the best fuel efficiency is noted. As the running temperature drops, fuel consumption rises. A 5C difference will have a discernable effect given a reasonable running period. The diesel is a cool running engine and would benefit (IMO) from a higher rated thermostat than the nominal 88C standard. With a new 88C stat, diesels seem to run around 88-92C, but rarely higher. In stationary traffic all engines will heat up, diesels included. The petrol engines also use an 88C thermostat, but typically run at 95-100C, eflecting their lower efficiency maybe, but they are also lighter and made from aluminium. I believe the massive cast iron diesel engine simply absorbs more heat without raising its temperature significantly. People have searched for a suitable stat of higher rating (say 90-94C), but without success thus far.
When diesel owners with a stuck open stat, running at 80C or lower get theirs up to 90C or so, a significant fuel saving is reported.

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Old 30-05-2010, 14:50   #7
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I had all the symptons - car running at around 76 degrees. After following all on this subject on the forum- I set up for jma-cars to replact the thermostat - I drove down to North Wales and met Julian - have to admit, he lives and breaths 75/ZT cars, in fact all Rovers. Wonderful guy. I got stuck in and worked with him - hopefully, all the way. Learnt such a lot and he also provided me with a lot of other information - Came over most caring and I am so glad that we have such people around. Along with Terry of TS we certainly struck oil. Two top men. As I should have my garage cleared in the next month or so, I will be tackling most jobs myself. Sorry Guys.
Left the Temperature reading on the Dash on all the way home (137 miles) and it was running at 91 - 93 degrees. Yes, the needle on the guage is now at 9 0'clock, period.
Both guys are, as far as I am concerned, Top men.
NB - Only hope I brought all my tools home....head scratching....
cheers and now for holidays in France/Spain.
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Old 30-05-2010, 19:59   #8
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Since the diesel is a BMW engined, would one of their thermostats fit our car, what is the thermostat fitted to the current 3-Series rated at, and would it not be suitable?.
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Old 30-05-2010, 20:33   #9
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Quote:
Originally Posted by zappas View Post
Since the diesel is a BMW engined, would one of their thermostats fit our car, what is the thermostat fitted to the current 3-Series rated at, and would it not be suitable?.
Hi; No they are different have a look here http://www.c3bmw.co.uk/StockItem.asp...&CategoryID=98
We have a BMW unit fitted to are cars (M47R) but the (M47N) engine which is fitted to the 320 D is different in a lot of ways, not all the parts will fit are cars, like thermostats/injectors ect, i think this is because the the engine is fitted in line, i replaced my thermostat only last week because the temp would rise above 78º now it runs at 90º/92º keep checking it if it drops below 80º then i would change it, Steve
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Old 30-05-2010, 20:47   #10
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I read a report on the other forum which validates what I've been saying about running temperatures. The diesel was historically running at around 77C and returning 49mpg. After a thermostat replacement the running temp went up to 91C and now produces an impressive 10mpg improvement. This equates to 800 miles per tankful (John O'Groates to Lands End if you like). It would almost certainly nudge 60mpg if it could be made to run at 95-100C. My daughter's Rover 220SDi always gave around 62-64mpg, though I accept it's a slightly lighter vehicle and a different engine.

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Old 30-05-2010, 21:52   #11
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Quote:
Originally Posted by top mg zt View Post
Hi; No they are different have a look here http://www.c3bmw.co.uk/StockItem.asp...&CategoryID=98
We have a BMW unit fitted to are cars (M47R) but the (M47N) engine which is fitted to the 320 D is different in a lot of ways, not all the parts will fit are cars, like thermostats/injectors ect, i think this is because the the engine is fitted in line, i replaced my thermostat only last week because the temp would rise above 78º now it runs at 90º/92º keep checking it if it drops below 80º then i would change it, Steve
Hi Steve i got new stat from howards garage on Ebay came in mg box but stat and housing is stamped BMW so it may be possible to buy from BMW dealerships.
Just a thought.
Looks like i will be ordering another checked my car today running at 72.
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Old 30-05-2010, 22:31   #12
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seems a bit low to me.. as above thermostat maybe stuck open.

as also above, engines normally round near to or around 100 degrees or over.

thats why they need to be pressurised so the coolant can go over 100 degrees and not boil.
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Old 01-06-2010, 15:26   #13
slimtim
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Quote:
Originally Posted by T-Cut View Post
I read a report on the other forum which validates what I've been saying about running temperatures. The diesel was historically running at around 77C and returning 49mpg. After a thermostat replacement the running temp went up to 91C and now produces an impressive 10mpg improvement. This equates to 800 miles per tankful (John O'Groates to Lands End if you like). It would almost certainly nudge 60mpg if it could be made to run at 95-100C. My daughter's Rover 220SDi always gave around 62-64mpg, though I accept it's a slightly lighter vehicle and a different engine.

TC
Wow, have to say that is pretty impressive. Sounds like the expense of a thermostat change would pay for itself in little time.
My 85c/86c constant running temp on the diesel is pretty borderline and will probably keep it as it is for now.
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