W203 Coolant Thermostat(s)? Sanity Check!

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Paul Goff

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The ACID test!

Drove from Exeter to Chesterfield a week ago with the whole of the radiator blanked off, ambient temperature 13 to 15C, quite a bit of sitting in queues. Kept a VERY close eye on the coolant temperature, it took the usual loooooong time to get fully up to 90 ish but then sat there controlling nicely all the way :)

Average speed 54MPH, average fuel consumption 52MPG.

Came back last night, no congestion, ambient was 2 to 3C, av speed 58MPH, av consumption 50MPG.
 

Droverunner

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Are you saying at an outside temp of 13+deg and a blanked radiator plus the new aux stat it took a long time to reach 90deg... because that is very much at odds with our far quicker warm up even at freezing point???
 
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Paul Goff

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Are you saying at an outside temp of 13+deg and a blanked radiator plus the new aux stat it took a long time to reach 90deg... because that is very much at odds with our far quicker warm up even at freezing point???
Afraid so! But it is SO much better than it was :) I am satisfied that what is happening now is a characteristic rather than a fault. The car/engine is a relic of days gone by, it doesn't have a Particle Filter for instance, it's very likely that fast warm up was not the priority it became on later models.
 
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Paul Goff

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It is electrical, yes - it's buried down the side of the block. I believe it's 1.7kW, which is a hefty number of amps at 12V, hence it only works when the car is moving.

Be interesting to know your findings on MPG - I've never really thought about it, and have always has it enabled.
Hi Rory,
I have had the electric Heater Booster enabled for several days now, and it seems to be working :)
Difficult to quantify I know, but I do think that I am getting heat into the cabin much sooner than previously. However the real give away is the fuel consumption immediately after a cold start! Without the booster I would see 32/33MPG on the half mile or so to the old London Road, with the booster, it's about 26/27MPG, and this pattern continues until the coolant gets to 70C and the booster is disabled! When it switches off the average consumption rapidly improves. It took about 6 miles until switch off just now.
All of which I would expect from an electric heater rated at 1700W!, that's nearly 2.5BHP :geek:

So, I reckon that it warms the cabin more quickly but is fairly heavy on diesel while it does so.

Question is, if one drives far enough for it to switch off, what effect, positive or negative, will it have on fuel consumption? ;)

My feeling is that, even at the price of a touch more fuel, anything that warms such a cold blooded motor up more quickly has to be good, mine is staying enabled.
 
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Paul Goff

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I wonder if we have one of those elec thingys which is skewing our experience... I must check.
It could be that you do, and, as part of the quest to achieve faster warm up and pass emissions testing, later cars do not have the option to disable it?

The time/distance to FULL warm up of turbo diesel engines has always seemed long to me. I have had TDs for over twenty years now and all the ones with a "trip computer" did much the same thing. Four or five miles to get the temp gauge up to "normal" but then, at twenty to thirty miles there would be a dramatic improvement in average MPG, often as much as 15%! before it settled to steady again at the better figure within another ten ish miles.

There have been ten cars over that period, two Renaults, four Peugeots, one Citroen, two VAG and now, one Mercedes, Most were company cars. They all had approx 2000cc engines, interestingly, the Mercedes engine is physically MUCH larger than the others! This MPG improvement occurs a LOT later in the Mercedes than the others, presumably because it has more mass? In the frigid conditions of Wednesday evening it didn't happen until 80 miles!!!
 

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Hi Rory,
I have had the electric Heater Booster enabled for several days now, and it seems to be working :)
Difficult to quantify I know, but I do think that I am getting heat into the cabin much sooner than previously.

>> I can back my car out of the drive, 200yds to the end of the road, another 200 yds to the village garage, and I'm starting to feel the air onto the screen get warm. "Warm" is relative, of course - I mean warmer than stone-cold.

Question is, if one drives far enough for it to switch off, what effect, positive or negative, will it have on fuel consumption? ;)

>> Yes, I do wonder where if there's a "break-even" point! I tend to mainly use mine for long journeys - a typical one is 180 miles, so even if there is a downside it's neither here nor there.

My feeling is that, even at the price of a touch more fuel, anything that warms such a cold blooded motor up more quickly has to be good, mine is staying enabled.

>> Agree with that! I've always used mine. Many (all now?) diesel cars have some kind of heater or they'd never get warm, but a lot are "hidden" with no user intervention possible.
 

om613

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I strongly suspect that it's there as much to facilitate fast warm up of the diesel/bio fuel as it is to keep it cool. The circuit does warm up pretty quickly.

Well done for finding it!
Can you see #14 under the bonnet, a heat exchanger linking this aux rad into the fuel circuit?
With bio more prone to waxing, in single figure temps, this is where heat would be beneficial. Ideally, all the way back to the tank, even that doesn't help the car start...

BTW, I've got the 6 cyl. version of your engine. I have run this mostly on bio for the last 23K miles. It should run at 90 C and get there after about 5 miles, or maybe a bit longer when it's this cold.
Then it stays rock solid. I've removed the mechanical fan on mine. Bottom and top covers have gone, too. And the electrical heater booster (commonly) doesn't work.
 
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Rory

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... this pattern continues until the coolant gets to 70C and the booster is disabled!

How do you know it goes off at 70C? Not saying that's not correct - I can't recall seeing the switch-off temp mentioned before.

I took my car out today for the first time in a while and although my home outside temp gauge said it was 7C the car thought it was 11.5C, so no booster heater. I drove a couple of miles on the flat, then a mile up a steepish hill at 60MPH and the car tried to do it 5th but I nudged it down to 4th. At the top the temp was 60C but it stuck at that for miles of rolling 50MPH roads - as usual it was a dozen or so miles before it was getting towards 80C.
 
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Paul Goff

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How do you know it goes off at 70C? Not saying that's not correct - I can't recall seeing the switch-off temp mentioned before.

I took my car out today for the first time in a while and although my home outside temp gauge said it was 7C the car thought it was 11.5C, so no booster heater. I drove a couple of miles on the flat, then a mile up a steepish hill at 60MPH and the car tried to do it 5th but I nudged it down to 4th. At the top the temp was 60C but it stuck at that for miles of rolling 50MPH roads - as usual it was a dozen or so miles before it was getting towards 80C.
I found the info buried deep in the Owners Manual, not easy to find or re find! I suppose that if the coolant is hot enough to allow proper control of the cabin heating then the extra load is not needed. Just as well that I had mine turned off completely until last week, with the coolant not getting up to 70C often it would probably have cost a fair bit in diesel :confused:
 

Rory

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How do you know it goes off at 70C? Not saying that's not correct - I can't recall seeing the switch-off temp mentioned before.

I took my car out today for the first time in a while and although my home outside temp gauge said it was 7C the car thought it was 11.5C, so no booster heater. I drove a couple of miles on the flat, then a mile up a steepish hill at 60MPH and the car tried to do it 5th but I nudged it down to 4th. At the top the temp was 60C but it stuck at that for miles of rolling 50MPH roads - as usual it was a dozen or so miles before it was getting towards 80C.

I did the same (at least for the initial dozen or so miles) in wife's 2 litre diesel VW Tiguan yesterday. That also has a powerful booster heater although its workings are even more of mystery than the Mercedes one.

It also has a false temperature gauge which, although marked in degree C might just as well say cold/normal/hot as the gauge is controlled by the ECU. But, it can display the oil temp in the cluster computer.

Monitoring that, it performed remarkably similar to the water temp gauge in my car, and over similar distances. It doesn't read at all until it's 50C (it's just blank) and then sat at 60C for ages, before gradually climbing up to 90C.
 

EmilysDad

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It also has a false temperature gauge which, .... is controlled by the ECU. .....

I don't think that's unusual these days. My Roadster's temp gauge is. EmilysMum's Citroen doesn't have a traditional thermostat, it uses an ECU controlled motorised valve :shock: ...... £160's worth! What numpty came up with that bright idea? :mad:
 

Rory

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I don't think that's unusual these days. My Roadster's temp gauge is. EmilysMum's Citroen doesn't have a traditional thermostat, it uses an ECU controlled motorised valve :shock: ...... £160's worth! What numpty came up with that bright idea? :mad:

I think most (all?) recent Mercs have electric water pumps - I presume they do the same function.
 

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