W203 Coolant Thermostat(s)? Sanity Check!

[Paul Goff]

It will be interesting to see if you can pull the old one apart and upload a pic.

I will give it a go!

 

[Droverunner]

I've just looked and our CLK 220CDI doesn't have this. In truth a bit disappointed not to be in the "funny silver thing at the front" club!

 

[Rory]

With my 203, it's the slow engine warm up that's the pain. I need 6-10 miles before the heater begins to work normally. Once 85 degs shows, it's rock steady and the heater works fine.

Have you got the electric booster heater enabled (although I gather they often fail on older cars)?

I start to feel warm air within a few hundred yards - the car has to be moving for the booster heater to work.

 

[13enzy]

You can get blockages around the heater matrix. We have had a good few 203's with this. You have to back flush it (from drivers side to passenger side)

Hi sorry to butt in, I have a Mercedes ML 270 cdi Auto 2002 model. The heat has gone in the cabin, the engine temperature on the dash was indicating and hovering around zero. Someone on the forum suggested that my thermostat needs changing.... I first decided to drain the old water, I then refilled with plain cold water and run the engine for 10 minutes, I repeated this process twice....As the thermostat was stuck in the open position, the flushing process was done COLD, as the engine never really heated up....I then drained the water and went about changing the thermostat ( WOW!...that was fun ) , what I did not know was that at the underside of the thermostat had a rubber tube with a metal insert which fitted into the thermostat and the engine....after thermostat was fitted the (new antifreeze) water was gushing out....I found out that the insert was lying on the engine block .....After that was rectified, I topped up the lost antifreeze and run the engine for 20 minute....I occasionally give it some revs for a minute or two whilst squeezing the hoses, and even took it for a short drive with the cap off to bleed the system, but....the heat in the cabin was still zero (non existence), however the engine temperature was now hovering at approx 89 degrees, this indicated to me that the old thermostat WAS actually faulty.....but still no heat!!!
I am now reading in your post that you think the heater matrix could be blocked and that you recommend to.....”To back flush it....from the drivers side to the passenger side” ???
As I am a complete bigginner I would appreciate if you could describe how to go about it step by step, and any other relevant information would be immensely appreciated .......Thanks.

 

[Paul Goff]

AND, THE IMMORAL OF THE STORY IS.............

IF, your car has this Auxiliary Radiator and Auxiliary Thermostat fitted, mine is a 2002 W203 C220Cdi 611 engine.
AND, it is not getting the engine up to temperature regardless of how far it is driven, it could be because the Auxiliary Thermostat has failed open!

Fitted a new aux stat this afternoon and the coolant is now getting up to temp, and controlling at about 90C, without any blanking off of the radiators
Fitting a new main thermostat, A 611 200 0615 "Thermostat", did not improve things at all!!

The aux radiator seems quite capable of providing all the cooling needed in cold weather, and it does not have to be all that cold, less than 10C can be low enough.

If all the above applies, fit a, A 005 203 3975, "Thermostat Element", £30 from a main dealer (who will tell you that your car does not have one fitted, only fitted to Biodiesel cars, none came to the UK) It took me an hour, and I'm all thumbs.
It took me most of a day to FAIL at fitting a new main stat

If you use a garage, insist that both be changed, a good spanner man should be able to do both inside 1.5 hrs.

Mine still doesn't warm up quickly, but that's a big improvement on not all.
Fuel consumption is back where it should be and the heating is controlling much better, presumably because it now has HOT coolant to play with

 

[Droverunner]

Well done Paul, great result... and you have proved the doubters (inc me) wrong.

If you can do pull the old one apart and chuck up a pic of the internal bits.

 

[Paul Goff]

From the top,
General view with the horns removed.
Auxiliary Thermostat.
Auxiliary Radiator.
Aux Stat playing peek a boo behind the horns.

Old Aux Stat x 3

[/ATTACH]

 

[Droverunner]

Thank you so much for that... really informative. That aux radiator is larger than I'd expected and... together with its to/fro pipework... I can now see how it could lose a lot of heat.

 

[Paul Goff]

Thank you so much for that... really informative. That aux radiator is larger than I'd expected and... together with its to/fro pipework... I can now see how it could lose a lot of heat.

I also have two 1000cc sporting Vtwin motorcycles, each has two radiators, the car's Aux Rad is about the same size as one of the bike rads. One of the two bikes produces nearly the same power as the car, so one of it's rads can dissipate the heat generated by some 65 BHP.

Therefore, if the car is idling along at 70mph, on a winter evening, with the aux rad in circuit all the time, it can keep everything too cold to open the main thermostat.

Should have thought of that to begin with, I'll get me coat!

 

[Paul Goff]

One regular journey I do is 23 miles of rolling A road to the M6, and it takes nearly all of those miles to get the temp to its normal reading. Once it gets there, mine is rock steady though at a shade under 85C - doesn't matter if it's freezing cold or I'm stuck in a jam on a hot day. I've always believed it's a normal direct reading analogue temp gauge but I'm not 100% on that. I've had the car since it was 6mths old and it's always been the same. The electric heater booster in the block works fine on cold days - I get warm air within a few hundred yards.

Interesting to compare to my wife's VW Tiguan with VW's latest (EU6) 2 litre diesel. The has a false temp gauge which gets its output from the ECU, so it's at 90C in 3 miles and apparently VW designed it to never budge from that unless the car seriously overheats. However the cluster computer can display the oil temp, and, same as my car, that takes in the region of 15 miles to get to 90C.

Hi Rory, My car does have the heater booster but I have disabled it using the dash settings. The owners manual suggests that not using it will save fuel! I didn't question it at the time, twas Summer, and therefore of no relevance

But now it's brass monkeys and every little helps It is electrical, correct? And is just a 12V electric heater, so, by helping to heat the interior it should allow the coolant to warm a little more quickly and, by adding some extra alternator load, give the engine a touch more work to do, also help warm up generally.

Will using it consume more diesel? If it does will it by be enough for me to notice?
OR
Assuming that I go far enough to get things up to temperature, will it save a little by speeding the warm up? Again, enough to notice?

Food for thought, I think I will go and re enable it!

 

[Rory]

It is electrical, correct? And is just a 12V electric heater, so, by helping to heat the interior it should allow the coolant to warm a little more quickly and, by adding some extra alternator load, give the engine a touch more work to do, also help warm up generally.

Will using it consume more diesel? If it does will it by be enough for me to notice?
OR
Assuming that I go far enough to get things up to temperature, will it save a little by speeding the warm up? Again, enough to notice?

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.

 

[JohnArnoldBrown]

1.7kW would be about 140A by my reckoning.

 

[Rory]

1.7kW would be about 140A by my reckoning.

Yep - the alternator can do a couple of hundred amps though. I guess that's why it's water cooled.

 

[JohnArnoldBrown]

Mine shows the aux heater on the dashboard setup, but I don't believe it's installed.

However, I took a look yesterday, and I do have that second stat, behind the horns. Didn't get a very good look, but is it plumbed into the hose with a couple of clips?
If so, it looks like a small enough job that I might attempt it myself. Having lived with this cold engine problem for nine years, I'll feel pretty stupid if it can be fixed for a £30 part!

Thanks anyway for the detailed thread, Paul.

 

[JohnArnoldBrown]

Well, I can't find anywhere to buy this part on line. Anybody have any ideas? I'm in Surrey.

 

[Droverunner]

Paul had to go to his MB dealer and get it ordered in from Germany... part A 611 200 0615. Make sure they show you a pic of the part they order or it may just come as the main stat.

 

[LostKiwi]

Try doing as Paul did - just cover the auxilliary radiator to stop air going through it. Alternatively clamp the pipe to prevent water flow to see if it fixes the cold running issue.

 

[JohnArnoldBrown]

I have covered the aux rad. I am a bit concerned about clamping the pipe, as it is fairly old(2003), and I don't want to damage it.

 

[Paul Goff]

Well, I can't find anywhere to buy this part on line. Anybody have any ideas? I'm in Surrey.

I got mine from the main dealer here in Exeter, they took a little persuading that my car had such a thing fitted though! The part number of the one I used is A 005 203 3975.

Easy to fit, even for me, just the two hose clips, which I even managed NOT to destroy
The thermostat is held together with a wire clip, if you point the sharp ends outwards it becomes difficult to put radiator blinds in, so I had to go back in and turn it so that the ends don't stick out!

 

[Droverunner]

Ahh so ignore the part number I gave in post #96 above. It appears some online resources are showing the image of the aux stat Paul fitted against the part number of the main stat.