W204 M271 engine coolant temperature on motorway

[cheapshots]

Hi all,

My 2012 C250 CGI coolant temps sits at 90 degree's when in town driving, however drops and stays constant at 80 degree's when I'm on a motorway doing 70mph.

Is this normal behaviour?

 

[Wighty]

My clk 200 m271 engine now that I have changed the thermostat a few weeks ago sits at 90 whatever I do .

 

[SunnyDee]

Yes its fine, I live near Heathrow and travel to Marlow every day on a C250 Coupé M271 engine. And around January time when we had -03 temp wise I saw my car thermostat go down to 70oC as the outside air was so COLD, even the ****** mirrors fogged up and I had to use the rear heated button to take the steam off.

 

[oigle]

Hi all,

My 2012 C250 CGI coolant temps sits at 90 degree's when in town driving, however drops and stays constant at 80 degree's when I'm on a motorway doing 70mph.

Is this normal behaviour?

The beginnings of thermostat failure. It will gradually get worse over time. When it gets down to 70, maybe time to renew.

 

[cheapshots]

Thanks for the replies. I took her out for a 1hr motorway spin today and the temp stayed at 90 this time. Strange, I'll definitely be keeping a close eye on this.

 

[Steve@Avantgarde]

Thermostat opening temps are 85-92'c for regular running.

 

[Botus]

EGR removal will make it run colder on a motorway

new way to understand things for me this year.... always knew diesel operation is very differently to a petrol (petrol must have a very tightly control air to fuel ratio or it'll run like a dog or go bang 14.7 parts of air to 1 of fuel by mass is normal running). Whereas Diesels can have pretty much as much air in at anyone time and you just add more or less fuel to give a different output. Which is why the respond so well to turbo charging.

The bit I'd never thought about till this year is in winter with air at 0C (or lower etc.) if you push shed loads of freezing air in, brand new thermostat or not, you can way overcool the engine till it runs like a dog, wears out, has horrendous emissions, the heater stops working and fuel consumption is ruined.

EGR removal makes this a certainty. The purpose of adding the hot exhaust gasses back in, is mostly to help keep combustion temperature where its supposed to be to over come all the bits I highlighted in bold...

 

[umblecumbuz]

EGR removal makes this a certainty. The purpose of adding the hot exhaust gasses back in, is mostly to help keep combustion temperature where its supposed to be to over come all the bits I highlighted in bold...

Someone correct me if I've got this wrong, buy I always understood that EGR operation reduces combustion temperature because recycled gases from the exhaust are inert, and therefore do not ignite on the compression stroke. Reduction of combustion temperature is what helps reduce N0x.

Disabling the EGR cycle will therefore allow hotter combustion, not cooler.

I think that the whole EGR principle is a complete engineering bodge. Thank goodness the EGR system is now beginning to disappear.

Umble

 

[oigle]

EGR removal will make it run colder on a motorway


The bit I'd never thought about till this year is in winter with air at 0C (or lower etc.) if you push shed loads of freezing air in, brand new thermostat or not, you can way overcool the engine till it runs like a dog, wears out, has horrendous emissions, the heater stops working and fuel consumption is ruined.

Sorry Botus but that is complete BS.
Regardless of egr removal, a properly operating thermostat will maintain coolant temp in an engine once it has reached operating temp. The egr removal will NOT make it run cooler. It WILL cause the motor to take longer to reach operating temp is all. The positives of better response and economy, along with vastly reduced black smoke and a clean inlet manifold instead of one gradually choking itself to death greatly outweigh the slow engine warmup. Engine warmup can be accelerated by running the internal ventilation system on recirc during warmup. This prevents that freezing air you mentioned from rushing through the heater matrix and cooling the fluid therein - that fluid being part of the whole coolant system.

Ian.

 

[Naraic]

^+1...have to agree. I ran my 320cdi without an egr...it ran so sweetly.

 

[Naraic]

if you push shed loads of freezing air in, brand new thermostat or not, you can way overcool the engine till it runs like a dog, wears out, has horrendous emissions, the heater stops working and fuel consumption is ruined.

So all those guys running with ice, to try and really lower the temp of the air into their turbo engines to increase performance etc, have in fact got it wrong?

Hot air into an engine is a problem not cold.

 

[LostKiwi]

Technically Botus is correct.
If the engine is drawing in very cold air and the heat generated from combustion of the fuel is low (as at idle) then the engine will never warm up irrespective of the thermostat being open or closed simply because the incoming air provides excess cooling in the bores.
As he states, the diesel engine (at least those without throttle plates) operates by adding fuel to a cylinder 100% full of air as every intake stroke will draw a full cylinder. This is why diesel engine have a vacuum pump - they have no manifold vacuum due to no throttle plate restricting the amount of air being drawn into the engine.

As long as the amount of air ingested cools the engine sufficiently the cooling system is not used.
As the load increases and the amount of fuel increases the amount of heat generated rises rapidly.

You can see this effect for your self.
Start two cars from cold side by side - one petrol, one diesel. Leave both idling on the driveway and see which one warms up first.
My diesel Defender could idle on the drive in mid winter for 15 minutes and still not move the temperature gauge (with a good thermostat). The V8 Range Rover on the other hand was warm inside 5 minutes.

As Botus says - its a fundamental difference in the way a diesel works compared to a petrol.

 

[LostKiwi]

So all those guys running with ice, to try and really lower the temp of the air into their turbo engines to increase performance etc, have in fact got it wrong?

Hot air into an engine is a problem not cold.

Cold air is a problem only when the engine isn't tuned for it - road cars running cold don't do well as consumption and wear increases and in carburetted engines fuel condenses on inlet tracts making for inaccurate metering and poor running. Competition and drag engines are a whole different ball game as the wear considerations are irrelevant due to the expectation of regular rebuilds anyway and fuel delivery is almost always via injection which doesn't have the same issues.

 

[oigle]

Technically Botus is correct.
If the engine is drawing in very cold air and the heat generated from combustion of the fuel is low (as at idle) then the engine will never warm up irrespective of the thermostat being open or closed simply because the incoming air provides excess cooling in the bores.
As he states, the diesel engine (at least those without throttle plates) operates by adding fuel to a cylinder 100% full of air as every intake stroke will draw a full cylinder. This is why diesel engine have a vacuum pump - they have no manifold vacuum due to no throttle plate restricting the amount of air being drawn into the engine.

As long as the amount of air ingested cools the engine sufficiently the cooling system is not used.
As the load increases and the amount of fuel increases the amount of heat generated rises rapidly.

You can see this effect for your self.
Start two cars from cold side by side - one petrol, one diesel. Leave both idling on the driveway and see which one warms up first.
My diesel Defender could idle on the drive in mid winter for 15 minutes and still not move the temperature gauge (with a good thermostat). The V8 Range Rover on the other hand was warm inside 5 minutes.

As Botus says - its a fundamental difference in the way a diesel works compared to a petrol.

Your theory is fine but we do not use our cars in this way. That example is like way the manufacturers use to produce economy figures which we all know are artificially produced. They are driven, not idled constantly, and as such produce sufficient heat to enable the engine to properly warmup if it has a working thermostat. I would bet plenty that no owner of a diesel in England with a perfect thermostat would ever fail to reach operating temp on a decent run at highway speeds, even in mid winter.
Using a blanking plate across the radiator to reduce heat loss from the engine compartment can certainly be a help in quicker warmup.

 

[Lambo_Pig]

Hi all,

My 2012 C250 CGI coolant temps sits at 90 degree's when in town driving, however drops and stays constant at 80 degree's when I'm on a motorway doing 70mph.

Is this normal behaviour?

I'd worry more about your carbon build up on the back of the pistons on a CGI engine rather than a slightly cooler running engine in top gear on a motorway (which is normal by the way)

 

[cheapshots]

I'd worry more about your carbon build up on the back of the pistons on a CGI engine rather than a slightly cooler running engine in top gear on a motorway (which is normal by the way)

Thanks! Any preventative measures you'd recommend RE the carbon build up?

 

[LostKiwi]

I'd worry more about your carbon build up on the back of the pistons on a CGI engine rather than a slightly cooler running engine in top gear on a motorway (which is normal by the way)

You mean back of the valves (the pistons don't get carbon build ups behind them unless something is very wrong!).

 

[LostKiwi]

Your theory is fine but we do not use our cars in this way. That example is like way the manufacturers use to produce economy figures which we all know are artificially produced. They are driven, not idled constantly, and as such produce sufficient heat to enable the engine to properly warmup if it has a working thermostat. I would bet plenty that no owner of a diesel in England with a perfect thermostat would ever fail to reach operating temp on a decent run at highway speeds, even in mid winter.
Using a blanking plate across the radiator to reduce heat loss from the engine compartment can certainly be a help in quicker warmup.

On the contrary we do use our vehicles like this. We sit in traffic on our daily commutes idling along at very low speed. A blanking plate will have minimal impact if the main source of heat loss is intake air.
On a decent run at motorway speed where the amount of fuel is increased I agree but how many commuters will touch a motorway let alone get a decent run on one in rush hour...?

Have you noticed all the questions about thermostats lately have been from diesel owners? Not a single petrol one?

 

[oigle]

On the contrary we do use our vehicles like this. We sit in traffic on our daily commutes idling along at very low speed. A blanking plate will have minimal impact if the main source of heat loss is intake air.
On a decent run at motorway speed where the amount of fuel is increased I agree but how many commuters will touch a motorway let alone get a decent run on one in rush hour...?

Have you noticed all the questions about thermostats lately have been from diesel owners? Not a single petrol one?

Sure have. But, have you also noticed that everyone who has replaced the thermostat has reported no further problems with running at proper temps?

I would imagine a cold air mass blowing past the motor would cause more heat loss than that ingested, but that is just a guess.

Ian.

 

[Lambo_Pig]

You mean back of the valves (the pistons don't get carbon build ups behind them unless something is very wrong!).

Hahahah Yup