W203 Coolant Thermostat(s)? Sanity Check!

[EmilysDad]

Yep that's how I feel. Recently I've given our cooling system and associated items a mid life overhaul with new stat, water pump, aux belt, alternator over run pulley, belt tensioner etc.

It is so quick to look at Ebay to see prices, brands, suppliers, delivery dates etc then have it arrive at the door over the next couple of days... compared with the hassle of phoning around, getting folks to look stuff up, wondering if they are looking at the correct part, visiting places all over town to collect... and in the main dealers having that stress at the counter of asking them the price of every part before knowing if it was reasonable value or not.... and looking a cheapskate if saying no it's too much I'm buying elsewhere.

I have an email address for the parts dept. I'll email them a link to a comparable part on eBay and ask if they can/will price match. Invariably they will.

 

[Lord_Lucan]

I have an email address for the parts dept. I'll email them a link to a comparable part on eBay and ask if they can/will price match. Invariably they will.

This is MB price-matching non MB parts on ebay and the like? Or MB matching MB parts online? Or am I way off?

 

[EmilysDad]

This is MB price-matching non MB parts on ebay and the like? Or MB matching MB parts online? Or am I way off?

Price matching other MB dealers on line e.g. Grangemouth

 

[JohnArnoldBrown]

I hope the new stat does the trick. My 2003 S203 takes about 1,000 miles to get to running temperature. Had a new stat fitted a couple of years back, made absolutely no difference.

 

[Paul Goff]

I hope the new stat does the trick. My 2003 S203 takes about 1,000 miles to get to running temperature. Had a new stat fitted a couple of years back, made absolutely no difference.

Me too! If it does not, you will be able to hear the naughty words there in Thames Ditton

 

[Steve@Avantgarde]

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)

 

[Paul Goff]

WHO'S RUDDY STUPID IDEA WAS THIS THEN? MY OWN!!!

Tried to fit the new thermostat today and after a couple of hours struggling to get at the fixing bolts had to give up and put it all back together.

I can only undo one bolt, have started to round off the head on a second and, as it's even more difficult to get at than no2, have left the third alone.

This is why I hate working on cars chaps

Any suggestions re' a good independent in/near Exeter? I have been using Avantegarde, in Clevedon, but 'tis a bit of a mission for a small job.

Goffy.

 

[Paul Goff]

PLAN B

Except that there is no plan B

Just back from a local friendly Independent in Newton Abbott, about 20 miles. They have fitted the new, genuine Mercedes thermostat for me and it seems to have made no difference at all The ambient temperature has barely made it to 6C all day and the temp display hasn't got to 80 in either direction.

My hand(y) gauge, when applied to the top hose, tells me that the display is about right.

Any ideas what to look at next chaps?

Goffy

 

[Tashman]

I think your car has the same engine as mine, the OM611?
I've had at least 3 new thermostats in this year, and 3 temp senders, in the hope of trying to get the engine to heat up.
I fitted the genuine Merc 87C one and the car would only get to 82C, so in the end I discovered that for the facelift cars they Mercs increased the stat temp to 92C. I've fitted that one now and the car now gets to 87C. It seems that the cars only can get to within 5C of their stat temperature in these cold conditions. It takes about 10 miles (15 mins) of mixed urban and dual carriageway driving to get that temp.
The trouble is that these CDI engines are too efficient and therefore don't make enough waste heat to heat up all that coolant very quickly, especially with the heater blower taking it away too.
Are you using the car's engine covers? They can make a very small difference because they have insulation underneath. I've added more insulation to mine. Also if you don't normally run the car with the undertrays, try refitting them for winter, to reduce the amount of ice cold air blowing around the engine. I'm now working on blanking off the front grill for the worst of the winter for the same reason. Good luck.

 

[Paul Goff]

A further update,

From a very cold start today, it took about 7 miles of gentle driving along the, now bypassed, London Road to get the temp display up to 60 degrees and 4 miles back again, but on the dual carriageway at 70 ish, to get to 80! However on the way down the big hill, just coasting in Drive, it dropped to about 70 again!

It appears to me that the new stat is behaving in exactly the same way as the old one, and therefore should I conclude that the old one was not faulty?

Interestingly, my last work van, a Transit Connect 90, did much the same thing, I could drive it around from job to job in town all day in winter and it would barely get warm enough to make the heater effective. It always took several miles of open road at a limited 60mph to get the temp gauge to vertical, and then half an hour in town would see it fall right back to just over "blue".
The garage that did our servicing were asked to change/check the stat, I don't know if they did, things did not get any better in the 5 years from new I drove it.

 

[Paul Goff]

I think your car has the same engine as mine, the OM611?
I've had at least 3 new thermostats in this year, and 3 temp senders, in the hope of trying to get the engine to heat up.
I fitted the genuine Merc 87C one and the car would only get to 82C, so in the end I discovered that for the facelift cars they Mercs increased the stat temp to 92C. I've fitted that one now and the car now gets to 87C. It seems that the cars only can get to within 5C of their stat temperature in these cold conditions. It takes about 10 miles (15 mins) of mixed urban and dual carriageway driving to get that temp.
The trouble is that these CDI engines are too efficient and therefore don't make enough waste heat to heat up all that coolant very quickly, especially with the heater blower taking it away too.
Are you using the car's engine covers? They can make a very small difference because they have insulation underneath. I've added more insulation to mine. Also if you don't normally run the car with the undertrays, try refitting them for winter, to reduce the amount of ice cold air blowing around the engine. I'm now working on blanking off the front grill for the worst of the winter for the same reason. Good luck.

Thanks for your input Tashman,

Mine does have the 611 engine, and as I am unwilling to spend more time and money on something which looks more and more like a characteristic rather than a fault, I am going to do much the same tomorrow!

My engine is still fully clothed top and bottom

 

[LostKiwi]

Diesels always struggle to get warm in winter.
A diesel engine ingests full cylinders of cold air on each revolution. The only way to get the engine warm is to add as much fuel to the air as possible. Gentle driving will therefore mean it takes ages to heat up and idling on the drive will never get it warm.
Don't nail it from cold but don't be over gentle. Just drive as normal to get the heat in.

I ran a diesel Defender with no water pump for 50 miles in winter with no issues some years back.

 

[Paul Goff]

Do I win the Cheque Book & Pen?

Ten minutes with a stout cardboard box and a pair of scissors! I now have an engine that gets up to temp in a reasonable time/distance and appears to be controlling at 85/90 degrees, without the fan starting The ambient here is about 10 degrees

You guessed it, I've Blanketty Blanked off the blanking radiator

needless to say I will be monitoring things VERY closely!

 

[Droverunner]

>>>It appears to me that the new stat is behaving in exactly the same way as the old one, and therefore should I conclude that the old one was not faulty?

Or the old one was faulty and so is the new one??

I know we have the 646 engine in our CLK so not exactly the same as yours but they are very very similar to my eye.... anyway our old stat behaved as your old (and new) one. Swapping it produced instant results which have been maintained through this cold snap.

Once the car has got warm... just a few miles even in cold weather... giving it a greater speed with lighter load does not reduce the temp on the gauge.... that is a feature of a radiator cooling the water because the stat is not fully closing. Ours just goes up to temp and stays there all trip.

Very odd.

 

[LostKiwi]

Do I win the Cheque Book & Pen?

Ten minutes with a stout cardboard box and a pair of scissors! I now have an engine that gets up to temp in a reasonable time/distance and appears to be controlling at 85/90 degrees, without the fan starting The ambient here is about 10 degrees

You guessed it, I've Blanketty Blanked off the blanking radiator

needless to say I will be monitoring things VERY closely!

This says water is circulating through the radiator when the thermostat should be closed. If the cooling system were functioning correctly what you have done would make little if any difference.

 

[ajlsl600]

kuma. swahili ,does it for me! kids know, grandkids dont.....

 

[Paul Goff]

I agree with you both but I am now between the Devil and the Deep Blue Sea with this.

Bought a new, genuine Merc stat, from a genuine Merc dealer.

Due to generally useless spannering skills, found I could not fit it myself. But have done so a few times in the distant past, on other cars (the old fashioned sort where you can nearly get in the engine bay beside the motor ) with complete success.

Had a local Merc independent fit it on Friday.

No discernable difference!

Three possibilities, in no particular order of probability.
The original stat was not faulty and I need to work round a characteristic of the car.
Or, The new stat has the same fault as the old one. How likely is this?
Or, There is something else wrong.

I can only test possibility 2 by taking the car back to the indy and throwing cash at the problem, the new stat, as it wasn't diagnosed or supplied by them, isn't their responsibility. So the labour costs would be down to me. They test it, find it's faulty and quite rightly hand it to me to take back to Mercedes Exeter and get another, or it is OK and they refit it. Either way I foot the bill

Tashman said in his post that his car has the same engine as mine, a 611. His has had 3 stats recently and still will not warm up, which tends to suggest to me that all this could be a characteristic, or that his car has the same "other fault" as mine.
JohnArnoldBrown has had a similar experience with his 203 220Cdi.

The bottom line is that it may be bodged for now but that has alleviated the symptoms. The car has a pressing need for a new steering rack and financially, I am not in a position to chase this elusive but non critical problem any further AND get a new rack fitted in the near future, I have to choose!

Don't get me wrong here guys, I really do appreciate everyones input, but I have to be pragmatic for now and live with the 'orrible pieces of cardboard Unless of course anyone has found, and fixed the "other fault", on the 611 engine???

Thanks again, Goffy.

 

[Rory]

From a very cold start today, it took about 7 miles of gentle driving along the, now bypassed, London Road to get the temp display up to 60 degrees and 4 miles back again, but on the dual carriageway at 70 ish, to get to 80! However on the way down the big hill, just coasting in Drive, it dropped to about 70 again!

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.

 

[Paul Goff]

OR EVEN..............Back to plan A!

Which was........peering suspiciously at the Auxiliary Radiator Thermostat.
I did several hours of searching old threads on here yesterday evening and have reached the conclusion that fitting a new one of these has to be the next step in my quest for the holy grail of a warm engine

My research also told me that getting one, even from a main dealer, might be a problem as they were "only fitted to bio diesel cars Sir, yours does not have one" Fortunately my search turned up the part number,

A005 203 3975

So for one blue + one brown beer token, one of these is on it's way from Germany! None in the country because GB cars don't have them. (apparently)

Cover me, Old Ten Thumbs is going in again

 

[Droverunner]

Paul do you have a link to the coolant diagram that shows this part and how it all works?