W203 Coolant Thermostat(s)? Sanity Check!

[umblecumbuz]

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)

That's interesting.
But surely that would not affect the thermostat opening, or the temperature reading on the display?

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.

On my 204 I have blanked off the grille - not the radiator - with a cutout sheet fixed behind it, much to Neyland MB's amusement as the receptionist thought that I'd hit something and got some cardboard debris lodged behind the grille!

In the Scandinavian group, radiator muffs are commonplace and main Dealers offer them. Stopping freezing air from howling through the radiator by muffing the grille is an accepted method of maintaining engine temperature.

A thermostat does not make heat. It only dissipates excess heat if any is there to dissipate. If the weather is too cold, then however efficient the 'stat is, the engine (and hence the heater) will not reach optimum operating temperature.

 

[ajlsl600]

surely if there is a closed stat it will eventualy boil, overheat, if the stat remains open the motor will only warm up and not reach operating temp ,if the op has changed the stat and it remains cold thats indicative of unresticted flow where alse can flow go on this engine, i gues the trans oil passes thru a cooler rad or a section of the main rad ? rad blinds were used on a number of early cars guess to maintain temps by restricting heat transfer thru, deliberatly larger than normal radiators ,no? cant quite get how the op is seemingly getting unrestricted water flow thru his cooling system unless there is a bypass that would also normally be restricted,and in his case is not .you say fuel burn now worse , maybe sensor somewhere is signaling more fuel as engine colder ?

 

[LostKiwi]

surely if there is a closed stat it will eventualy boil, overheat, if the stat remains open the motor will only warm up and not reach operating temp ,if the op has changed the stat and it remains cold thats indicative of unresticted flow where alse can flow go on this engine, i gues the trans oil passes thru a cooler rad or a section of the main rad ? rad blinds were used on a number of early cars guess to maintain temps by restricting heat transfer thru, deliberatly larger than normal radiators ,no? cant quite get how the op is seemingly getting unrestricted water flow thru his cooling system unless there is a bypass that would also normally be restricted,and in his case is not .you say fuel burn now worse , maybe sensor somewhere is signaling more fuel as engine colder ?

The way the coolant system works is we have a pump and a bypass. When the stat is closed and the engine is not up to heat all the water from the pump goes through the bypass. This is usually the heater circuit but may be a separate bypass completely. A bypass of some kind is required to permit water flow around the engine to prevent localised hot spots.
As the engine heats up the hot water starts to circulate around the bulb in the bottom of the stat. The heat causes the wax inside the stat to expand and once there is enough pressure inside the bulb to overcome the spring tension the stat will start to open. Once the stat opens water flows through the radiator and cold water enters the engine. This is heated by the fuel being burnt as the engine runs and is circulated by the pump back up to the stat. If its now too cold the wax in the stat will contract and the stat will start to close. The water flow is restricted so heats up again and the stat will reopen and so on. The stat is designed to be slow acting so that you don't get great surges of hot then cold water flowing round the cooling system causing thermal shocks.

Hence, until the stat opens the top radiator hose should be cold (cooling systems rely on a pump assisted thermo-syphon effect where hot water rises and cold water falls so hot water at the top of the rad will drop to the bottom of the rad as it cools provided a natural circulation - in the old days cars had no water pumps and the thermo-syphon was all there was for cooling). A thermo-syphon on its own is to a certain extent self regulating as the system flows faster with more temperature differential between hot and cold sides of the radiator and slower when there is none however in extremes of temperature it leads to overheating (boiling was a common issue on hot days) or over cooling (necessitating the use of a blind to reduce the efficiency of the radiator).

The bypass is the reason why the heater gets progressively warmer instead of being cold, cold, cold, cold, hot when you first start the engine in the morning.

 

[Paul Goff]

surely if there is a closed stat it will eventualy boil, overheat, if the stat remains open the motor will only warm up and not reach operating temp ,if the op has changed the stat and it remains cold thats indicative of unresticted flow where alse can flow go on this engine, i gues the trans oil passes thru a cooler rad or a section of the main rad ? rad blinds were used on a number of early cars guess to maintain temps by restricting heat transfer thru, deliberatly larger than normal radiators ,no? cant quite get how the op is seemingly getting unrestricted water flow thru his cooling system unless there is a bypass that would also normally be restricted,and in his case is not .you say fuel burn now worse , maybe sensor somewhere is signaling more fuel as engine colder ?

There is flow which bypasses the main stat, according to the diagram I posted earlier this week, this goes to,

Oil cooler/transmission fluid cooler
Heater matrix
Fuel cooler
Heater booster
Generator
Windscreen wash fluid reservoir
AND
Auxiliary radiator, via it's own in line stat. I am pretty sure this stat has failed open on my car.

 

[umblecumbuz]

Remember the old Lister stationary diesel engines?
They would thump away all day under UK blazing(!) summer skies, and their only cooling was a finless water jacket round the cylinder with an open top. Water was poured into the open top and left static. It circulated by thermosiphon as Kiwi describes, and even open to atmosphere it rarely reached boiling point (pressurised cooling systems boil at higher temperatures of course).
No pump, no radiator, no pipework. Not the best example, but it serves to show that oil burners often produce very little excess heat.

Oil burners up in, say, Finland need all the help they can get in winter with minus double figures to maintain engine temperature - hence radiator muffs.

 

[Droverunner]

>>> oil burners often produce very little excess heat.

Yes but in an average UK winter they should still warm up to stat temp promptly and produce a decent heater output.

 

[ajlsl600]

got that. so the actual cause of his problem is? given stat changed fan ok and water pump must be working? cant see it being trans cooler ,or alternator( w168 also water cooled) or windscreen washertank. seems to leave heater and booster, is there a schematic of that? most motors i have ever had warm up in about ten min. starting to sound like overcomplication .

 

[Paul Goff]

got that. so the actual cause of his problem is? given stat changed fan ok and water pump must be working? cant see it being trans cooler ,or alternator( w168 also water cooled) or windscreen washertank. seems to leave heater and booster, is there a schematic of that? most motors i have ever had warm up in about ten min. starting to sound like overcomplication .

Hi AJ,

There is a schematic I posted about 10 comments ago, I would rather not try to repost it, my IT skills are somewhat worse than my spannering ones, and that is saying something!

It is for biofuel 611 engines, Mercedes UK reckon that they never imported diesel models thus fitted, but my car begs to differ

Thermostat 18/3 has failed open on mine, I have one on order via MB Exeter, from Germany, I nearly had to take my car to the dealer to show the man! "Not fitted to your car Sir" And there the discussion would have ended if I had not been able to supply the part number I had gleaned in my searches on here!

 

[ajlsl600]

yr rightly exasperared, cant wait to understand actual cause will look yr earlier post ref schematic .

 

[Droverunner]

Can't wait for your part to arrive and get fitted. Despite studying the diagrams and reading all online info I'm still struggling a little with the step by step understanding of how these extra cooling circuit options interact as it warms and cools... but very much hope that against the expectation of many inc myself it does the trick.

 

[LostKiwi]

got that. so the actual cause of his problem is? given stat changed fan ok and water pump must be working? cant see it being trans cooler ,or alternator( w168 also water cooled) or windscreen washertank. seems to leave heater and booster, is there a schematic of that? most motors i have ever had warm up in about ten min. starting to sound like overcomplication .

Somewhere in the bypass circuit is something providing significant cooling and from the diagram above it can only be the auxiliary radiator (hence the suggestion to cover it. For that matter you could disconnect it and block the lines as well to prove the point as there is sufficient bypass elsewhere to keep everything running as it should (and we already know its not required). I also suspect the auxiliary stat is failing to close not failing to open.

 

[Paul Goff]

Somewhere in the bypass circuit is something providing significant cooling and from the diagram above it can only be the auxiliary radiator (hence the suggestion to cover it. For that matter you could disconnect it and block the lines as well to prove the point as there is sufficient bypass elsewhere to keep everything running as it should (and we already know its not required). I also suspect the auxiliary stat is failing to close not failing to open.

That's "failed open", old chap, not failed TO open.
I will wait for the new aux stat to arrive and fit it, I SHOULD be able to manage that all on my own. (he said foolishly!)

Meanwhile I have waterproofed the cardboard with packing tape (no expense considered) It's been very rainy here, things were getting soggy

PS, are stats generally designed to fail open? I always assumed so.

 

[LostKiwi]

That's "failed open", old chap, not failed TO open.
I will wait for the new aux stat to arrive and fit it, I SHOULD be able to manage that all on my own. (he said foolishly!)

Meanwhile I have waterproofed the cardboard with packing tape (no expense considered) It's been very rainy here, things were getting soggy

PS, are stats generally designed to fail open? I always assumed so.

Ah yes - my bad!
In general stats are designed to fail open.

 

[ajlsl600]

do advise outcome.....

 

[umblecumbuz]

Fancy using cardboard when there are For Sale signs lying around!
Great material for rad muffs. Light, easily cut, weatherproof and bendable!
I sprayed mine with blackboard black.

 

[ajlsl600]

Fancy using cardboard when there are For Sale signs lying around!
Great material for rad muffs. Light, easily cut, weatherproof and bendable!
I sprayed mine with blackboard black.

a true scavenger.
i just bought an A class 03 170cdi auto runner with yr mot for 100. if that makes it accross chanel ferry next week with its 4x new tyres, and the xmas gooodies from b and q ,sainsburys i will be well pleased .... donner for lovelly,s A 170

 

[Paul Goff]

And here it is, in all it's silver shinyness. It will allow a TINY amount of air to be blown through it in the direction of the arrow, so closed, and clearly intended to open when the coolant gets hot enough.

 

[Droverunner]

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

 

[SRE]

Certainly doesn't look difficult to fit (assuming you can find the old one) so hopefully will be a quick cure.

 

[Paul Goff]

Certainly doesn't look difficult to fit (assuming you can find the old one) so hopefully will be a quick cure.

By car standards it's very easy to get to, in front of the main radiator, in the low middle ish, behind the horns