W203 Coolant Thermostat(s)? Sanity Check!

[Tashman]

Yes I'd be interested in that too.
I've never heard of this Auxiliary Radiator and Auxiliary Thermostat before?
I think my car has 5 rads on the front: the coolant rad, the engine oil rad, the intercooler, the AC rad and the trans cooler.
Although my car takes a long time to reach operating temp (15 mins), when it gets there, it never drops at all regardless of how you drive it, which is what is worrying me about your description - you say that if you slow down, it cools back down again, which might suggest your thermostat is not closing in response to the reduction in heat?
Out of interest, roughly what percentage of your radiator did you blank off?

 

[Paul Goff]

Bear with me Droverunner, I will see what I can do! IT stuff isn't my strong point though

 

[Paul Goff]

Yes I'd be interested in that too.
I've never heard of this Auxiliary Radiator and Auxiliary Thermostat before?
I think my car has 5 rads on the front: the coolant rad, the engine oil rad, the intercooler, the AC rad and the trans cooler.
Although my car takes a long time to reach operating temp (15 mins), when it gets there, it never drops at all regardless of how you drive it, which is what is worrying me about your description - you say that if you slow down, it cools back down again, which might suggest your thermostat is not closing in response to the reduction in heat?
Out of interest, roughly what percentage of your radiator did you blank off?

ALL of the radiator is now blanked off.
The schematic refers to the small radiator in front of the main radiator, on the right in direction of travel as the Auxiliary Radiator.
It's thermostat, a little in line device like a filter is also in front of the main rad. in the middle, low down and behind the horns.
i will TRY to post a link to the schematic.

 

[Paul Goff]

There we go chaps, originally posted by roxie several years ago, you might get a less fuzzy image by searching in roxie's posts.

As one can see, there are a number of items that coolant flows through irrespective of the position of the main thermostat.

6, oil/transmission fluid cooler
8, heater matrix
14, fuel cooler
18, auxiliary radiator
A6, heater booster
G1, generator (the alternator, REALLY!?!?!?)
S, screenwash heater
AND
N33/2, ?????Webasto heater? A Webasto is the only item which I am sure my car does not have!

Quite a formidable list, may I postulate that, if the stat for the auxiliary rad (18/3) is permanently open, as mine is, this is sufficient to prevent the engine warming up enough to disturb the main stat from it's slumber if the weather is cold and I drive gently, as I nearly always do?

 

[Droverunner]

Very much appreciate the diagrams. I have no idea if our CLK has this system as it's still up to its headlamps in snow 100mls away so can't look.

I would love for anyone who really understands the system to describe its stages of operation as the car heats up and/or the external temps change.

I wonder what operates the behind the bumper stat you are swapping? It seems so far from the engine with a small bore feed surely it cant rely on the engine heat transmitting all that way. Perhaps it's an air temp stat??

Really interesting.

 

[Paul Goff]

Very much appreciate the diagrams. I have no idea if our CLK has this system as it's still up to its headlamps in snow 100mls away so can't look.

I would love for anyone who really understands the system to describe its stages of operation as the car heats up and/or the external temps change.

I wonder what operates the behind the bumper stat you are swapping? It seems so far from the engine with a small bore feed surely it cant rely on the engine heat transmitting all that way. Perhaps it's an air temp stat??

Really interesting.

During my searching I found that someone had replaced it, they found that the old one had no resistance to being blown through and the new one allowed some bleed. So it's most likely to operate on coolant temp.

On my car that circuit, and it's radiator, reflects the temp displayed on the dash pretty closely (since I have been paying attention, never high enough to open the main stat), while the main top hose seems quite a bit cooler.

 

[Droverunner]

What I really don't understand its the purpose of the aux stat/rad?

 

[ajlsl600]

daft, but if yr not getting up to temp after stats drama ,can you not try an old fashioned rad blind to find a decent winter running temp .?

 

[JohnArnoldBrown]

I think he's already done that.

 

[Paul Goff]

What I really don't understand its the purpose of the aux stat/rad?

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.

 

[Paul Goff]

daft, but if yr not getting up to temp after stats drama ,can you not try an old fashioned rad blind to find a decent winter running temp .?

Two 'orrible bits of carboard now sit in front of the radiator, the auxiliary radiator and the aux stat, but behind the wavy metal pipe which I think is something airconditioning related?
The two cards overlap by about an inch so that one or both can be slid sideways to get air through if necessary

 

[ajlsl600]

yup not really how to do things, but do you get the desired effect ? one might be able to work back wards from that..

 

[ajlsl600]

I think he's already done that.

ah, right ... one would have thought that cooling system would run pretty warm when rad covered ,are we suggesting that this engine does not need much ,if any rad ,that would be bizzare in function and design. .what kind of fan does it have viscous or ? is that working correctly.

 

[Paul Goff]

ah, right ... one would have thought that cooling system would run pretty warm when rad covered ,are we suggesting that this engine does not need much ,if any rad ,that would be bizzare in function and design. .what kind of fan does it have viscous or ? is that working correctly.

The blanking off of the radiator has greatly improved things but I am aware that I may well be alleviating the symptoms not curing the illness

The car was at Independent Mercedes Hospital, as a day Case, within the last week, in the hope of a cure
She had a main heartmostat transplant, a new, genuine, with sensor was fitted, but this made little or no difference!

Hence the need to pursue other possibilities.

This all started about a month ago, on a 50 mile each way trip, the fuel consumption was higher than I had been getting up till then. On the return journey I monitored the coolant temperature, it never got above 70 degrees. the ambient was about 5 degrees, first distance done in cold weather since I got the car.

 

[ajlsl600]

completely agree on cardboard curtain,does that car have a viscous fan drive ?

 

[Paul Goff]

completely agree on cardboard curtain,does that car have a viscous fan drive ?

I am fairly sure that the fan is electric, from what I can see of things there is only an electric motor, this drives the fan directly, there is no mechanical or hydro mechanical connection between the engine and fan. I do confess that I don't have a very clear concept of what a viscous fan drive is though

Since the long thirsty drive, I have yet to see the fan run, and I have stopped and investigated this, among other things, a couple of dozen times.
I don't know at what coolant temperature the fan should start, I assume that it will be several degrees above the main stat rating which is 92C. The coolant has not reached 90 since the cold weather arrived, I wouldn't expect the fan to run in these circumstances.

 

[LostKiwi]

The thing is if the coolant system is functioning correctly a radiator blind should make no (or at least minimal) difference. If the water doesn't flow through the radiator (thermostat shut) then it won't be affected by the radiator and the presence or non-presence of a blind. The only way the radiator can affect temperature is if water is flowing through it.
Out of curiosity, block the airflow for the auxiliary radiator only. What happens to temperatures then?
Also when the engine is at 70 degrees feel the top radiator hose. It should be cool to touch if the thermostat is shut.

 

[mercedes13156]

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.

I used to run a 1.4 Polo TDi and it blew a bottom hose in St Andrews. I came back to the car to see the coolant running down the street. The breakdown folk were very busy with it being spring a holiday weekend and said they'd be hours, so I filled it up with seawater from the harbour and set off home, the weather being cool and wet. The refill lasted a few miles until I got to a garage where I filled it again. That just ran straight through onto the forecourt, so I thought I'd see how far I could get before the engine started to sound like it was in trouble. I planned to stop, let it cool down then get home in relays. Surprise! I managed the entire 65 mile journey in one go without any water in the system by driving steadily at 40mph in top, doing about 1200 rpm. Next day I drove it to the dealers, bought a new hose and fitted it before driving to work. No problems. I washed the salt out and refilled it with proper coolant the next weekend and it never gave me a minutes concern.

 

[mercedes13156]

My current daily donkey, a Ford Kuga 2.0 litre diesel warms up to operating temperature in about a mile and a half with warm air after about a minute.

 

[Droverunner]

Mrs D has just this morning been able to get to and drive our CLK that has been under snow up to its headlamps for three days. It was idling for about 5mins while she removed the last of the snow and let it demist inside. Then she went just 3miles to her first stop and it was up to 90deg on the gauge with a toasty warm heater by the time she arrived. After an hour standing it went on a 6 mile trip and was up to 90deg again before halfway.

Once it had reached 90deg and was being driven despite it cruising gently and with cold outside air at no time did the gauge drop from 90deg.

For me that is a standard performance for pretty well any car diesel or not and what I'd expect. If I had any car that was failing to behave roughly like this I'd be checking the main stat for sticking open/partially open... even if the stat was new.

A test I often do for any car with possible stat issues is to allow the car to warm up from starting on the drive and keep checking the rad. If it feels anything other than cold prior to the stat opening temperature then the stat must be letting by.

As LK says if blanking a rad is a "cure" then the rad must be getting heat that shouldn't be there.