Engine: D52447: Thermostat replacement - Guide

[galloot633]

just remembered, the dealer told me the later engine (185) required the complete housing , but the early model was a standard thermostat swop
dave

[400-ascona]

For once on the T6 I can claim one up on you D5 boy's! The T6 stat is only £14 from the dealer! Mind you changing it is another matter!
Rob

[BestGear]

Originally Posted by 400-ascona

For once on the T6 I can claim one up on you D5 boy's! The T6 stat is only £14 from the dealer! Mind you changing it is another matter!
Rob

Yeh, I think its a cam belt off job - yes?

[BestGear]

Originally Posted by galloot633

dave
..... as it turned out there was nothing wrong with the car, just me new to diesels and their warm up time
dave

Yes, these damn things do take a while to heat up...especially if just left idling....

Mine is obviously now a lot better, but assume its now like everyone elses - in that heating up left idling takes ages...?

David

[400-ascona]

Originally Posted by BestGear

Yeh, I think its a cam belt off job - yes?

No, but its cam cover off job. I did ours when swapping the gearbox, so the engine was lowered anyway, but can't see how you would do the cam belt or stat without at least lowering the passenger side of the subframe.
Rob

[galloot633]

Originally Posted by BestGear

Yes, these damn things do take a while to heat up...especially if just left idling....

Mine is obviously now a lot better, but assume its now like everyone elses - in that heating up left idling takes ages...?

David

I still cant get my head round the warm up, every one of my cars up to the xc were petrol , so although i never deliberately let them idle to warm up , the first time i got stuck in traffic, no airflow hence no cooling and a faster warm up, whereas when I get stuck in traffic with a cold diesel the temp started to drop ! , during the cold snap mine took 6 miles to get up to temp
dave

[Jim314]

The long warmup is a result of the greater efficiency of the diesel engine. Diesels put out much less waste heat in the ehaust and to the coolant. In fact, long idling sessions can cause excessive wear because the engine temp in many diesels will not stay in the optimum range of operation if slow idled for an extended period.

Some manufacturers offer a 'high idle' selection for extended idling. I don't know if Mercedes offer this in their consumer diesels, but they did offer it as an option in their commercial passenger vans sold in the US as the Dodge Sprinter.

It could be that the cold engine wear problem was much more of a problem with the prior generation of motor oils, and is much less of a problem using full synthetic 0W-30 or 0W-40.

[BestGear]

Originally Posted by Jim314

The long warmup is a result of the greater efficiency of the diesel engine.

Without starting a heated debate, I still dont wear that!

I too have heard/read it, but if its true, then why dont all modern diesels do the same?!?!

I have a BMW 530D, and it heats up quickly - left to idle or not. Infact the later 5 series dont even have a temperature gauge on the dash (ok, there is a hidden one in the OBC).

If I watch the temperature of my beemer, it rises quickly to 75ish degrees C, then on to 88-90 very soon after and stays at that temperature most times unless at speed where it falls due to the inrush of cold air at the front of the car. Having said that, it even has ECU controlls blinds on the radiator to prevent cold air getting to the radiator until warmed up!

The efficiency of the diesel engine is much lower when running cool - hence higher fuel consumption.

My XC is now much warmer but its still pants - and for a car that came from coder climate than here! (ok, I know about opre heaters etc, but thats for exterme cold, not your average uk winter).

The heater is the biggest negative of the whole car, to me.

David

[Jim314]

No danger of heated debate from me, especially on automobile subjects.

I haven't tried to find any info on it, but could it be that BMW have implemented some new features in the cooling system to ameliorate the problem of slow warmup of the diesel? Do they have a special low volume cooling system in the engine which is compensated for with a high flow water pump or an extra large radiator to provide higher heat removal when that is needed? The blinds over the radiator could be part of a newer system to manage cooling.

Maybe BMW have implemented an extended fast idle after a cold start. My petrol Volvo only fast idles at 1200 rpm (in Park) for 10 s or so after a cold start. What about your Beemer?

On the question of waste heat in the exhaust, I have seen references to diesel engine exhaust being "over 100 degrees" cooler than petrol exhaust (don't know if this is real degrees or the nutty Farenheit system we are forced to use over here by the anti-progress troglodites that run this place). The explanation I have always heard is that the much higher expansion ratio of the diesel (>= 17 to 1) cools the combustion gasses much more than the less than 11 to 1 of the petrol engine. This fits with the claim that the high efficiency of the petrol engine in the Toyota Prius is partly due to its employing a version of the Aktinson cycle with an expansion ratio of 13 or 14 to 1.

I made the guess that lower temperature of the exhaust would mean lower waste heat in the exhaust, but of course a dlesel may more than compensate for this due to higher mass flow of exhaust at lower power outputs, since the air intake in a diesel is not throttled. At idle a diesel engine may have a 100 to 1 air-fuel ratio whereas a petrol spark ignition engine is alway going to be around, what 14 to 1?

[BestGear]

Hi Chaps

I thought I would update the thread with some interesting info.

Although the car now heats up much quicker with the new thermostat, its interesting to see some data on this.

The car seems to get warmer only when driven, and plateaus or falls when the car is at idle.

It also never seems to get hotter than 87 degrees which is strange as the thermostat is a 90 degree unit from memory, so if that is true, then the thermostat would never open. perhaps the marked temperature is when its fully open, NOT when it starts to open? An inaccurate temp sensor (was replaced with thermostat housing) could also account for this reading.

Anyway - the data below shows that on the drive to the office this morning, it took 13mins to reach 87 degrees and that included 3 mins at idle (or very near to).

Its interesting to see the air intake temp rose when idling - this may be the cars own heat, or possibly heat from the car in front in the queue!



Anyway - one to study....

David