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@Mmr1 You are definitely correct in the fact that diesel contains more energy per unit than gasoline. Following your logic, diesel would burn hotter than gas if they’re to burn at the same rate. However, our engines used metered injection both gas and diesel, therefore they do not consumed at the same rate for optimized combustion for the same output in power. This is why Diesel engines in most cases gets better fuel economy. Use less fuel, less heat - like the LED analogy.
Last edited by stickman007; Dec 30, 2021 at 08:54 AM.
It is not uncommon for a Diesel to run colder than the thermostat setting in cold weather. At least part of that is due to the increased efficiency of the Diesel cycle. If the engine wasted as much energy in heat as a gas engine, it wouldn't get better mileage. If the new thermostat doesn't solve the problem then I'd just block off enough of the radiator to get the right results.
Not true, diesels get better milage only because diesel fuel has About 15% more energy. Diesel do not run cooler, their operating temperature is not a factor of fuel type but engine construction.
Conducted my own test today too. Drove home with manual shifting keeping rpm 2k-2.5k. I was able to keep the coolant temp close to 75C in the city and even 85C on the highway - outside temp was -26C. Whenever I go back to auto, the temp drops back down to 60-70C
Yesterday was -21C and I had no issues getting to 85C on the highway even without manual shifting. I’m trying to be more conscious of my temp as Mmr1 pointed out, need to be above 76C for sometime to cook the crap out.
I’m curious to see the difference after the thermostat and oil change. I have a 2.0t gasser VW….it has no issues with warm up in the cold. I think its a diesel thing, as the engine makes less heat. We shall see, I called the dealership today and they said that the thermostat in tomorrow. I picked up a butt load of maintenance stuff - trans service, diff oil, engine service (229.52 oil). The only thing I’m lacking now is the G05 coolant. I’ll be busy this wkend!
@GLK Super Fan how do u know that your pipe is split? Engine code? Lacking power?
Ya i have the cel. And the codes shows issue with MAF. I had this happen to me once before. I am just not too sure which side is it. Hopefully it the driver side, little bit cheaper
Not true, diesels get better milage only because diesel fuel has About 15% more energy. Diesel do not run cooler, their operating temperature is not a factor of fuel type but engine construction.
We'll have to agree to disagree on that. Otherwise I'd have to go back over 20 years of students and tell them that I and the text books were both wrong.
Here's another guy who puts it more succinctly than I: Andrew Forrest, Chief Engineer at Solstad Offshore (2005-present)
Q. How much energy is lost to heat in diesel engines compared to gasoline engines?
A. A typical petrol engine has a thermal efficiency of 25%, whereas a diesel will be around 30 to 35%. This explains why diesels are more fuel efficient compared to petrol engines, they waste less of the fuel in generating waste heat.
Note that the difference between 25% and 35% represents a 40% increase, not a 15% increase. (a 10% improvement is 40% of the 25% efficiency of the gas engine.
It was -28C outside this afternoon and -5C in the garage (haven't hooked up my heater yet). Changed out the thermostat - took around 3hrs, figured I'll just wing it...it was a fight as I didn't have any good pilers to take those spring hose clamps off in tight spaces. Need to start collecting some good tools at home!
I noticed something potentially bad...I don't know what coolant I have in there! Its definitely not G05. Its kind'a bluish (like my Smart Car), but has a tinge of green and yellow. I'm guessing at some point somebody added the wrong coolant in there? I guess will also need a coolant flush as soon as the weather warms up slightly enough to run a hose through and engine warmed up.
Will report back to see if there's any improvements to the coolant when driving to work.
It was -28C outside this afternoon and -5C in the garage (haven't hooked up my heater yet). Changed out the thermostat - took around 3hrs, figured I'll just wing it...it was a fight as I didn't have any good pilers to take those spring hose clamps off in tight spaces. Need to start collecting some good tools at home!
I noticed something potentially bad...I don't know what coolant I have in there! Its definitely not G05. Its kind'a bluish (like my Smart Car), but has a tinge of green and yellow. I'm guessing at some point somebody added the wrong coolant in there? I guess will also need a coolant flush as soon as the weather warms up slightly enough to run a hose through and engine warmed up.
Will report back to see if there's any improvements to the coolant when driving to work.
Hey buddy, can you provide some instructions/tips how did you replace the thermostat? Thanks for giving the update.
Not sure if the procedure is cover else where already - pretty straight forward as thermostats go, but here it is.
Thermostat Replacement GLK250 BT:
1) remove the “s” air intake pipe by unclipping it.
2) remove the engine cover by turning the lock tab with a screw driver at the front, lift the front and sliding the rear out of the guides.
3) remove the lower front tray from under - 8mm screws. Didn’t count how many though…maybe 10?
4) drain coolant from the LHS corner of the radiator. There’s a twist knob that u turn 180 degrees. I did not do a full drain, only about 4L just not to make a mess.
5) carefully unlock tabs holding the plastic harness tray to gain more access to the thermostat. Pull the tray a few inches higher.
6) disconnect coolant temp sensor, and 2 other connectors that I haven’t paid attention to what they are to allow more room to lift the harness tray.
7) there’s 3 bolts holding the thermostat on the cylinder head (2 on the front, and 1 on the side), remove them. The bolts have metal brackets on them, remember their location. There is also 1 bolt that holds a plastic piece on besides the oil filter cap that will need to be removed. All the bolts were torx, you’ll need either etorx sockets or I just used a 8mm regular socket.
8) pop the wire lock for the upper radiator hose on both ends and remove the hose completely.
9) using whatever pliers or special tool u have to take the tension off the spring hose clamps and remove hose starting with the 2 smaller ones.
10) there are 4 hose connections all together - 2 big and 2 small ones.
11) Install is the reverse of removal pretty much. Be very careful not to snap or crack those brittle plastic electrical connector locking tabs!
12) I refilled the coolant until the reservoir was almost full, then I squeeze the upper coolant hose a few times and got some air out. I also cycled the ignition a few times to get the coolant circulating pump to help me force some air out.
13) I pretty much was able to put the same amount of coolant in as what I took out. Will probably need to drive it in the morning up to temp to fully bleed it.
Thermostat bolts are torqued to 9Nm.
Give me a shout if you have any questions or if I miss something big and my engine will blow up soon!
Last edited by stickman007; Dec 31, 2021 at 11:08 PM.
As far as I know, G05 isn't the right coolant. Mercedes used MB 325.0 and 326.0 in cars built through April of 2014, and 325.6 and 326.6 in cars built starting in May of 2014. The 325 series is concentrate and 326 is pre-mixed coolant.
As far as I can tell, the early cars use G48 (meets MB325.0), which is blue, and the later ones may use G40, which is pink. Most pink coolants say they meet MB325.5, not .6, so IDK. Fortunately for me mine is early...
Last edited by John CC; Jan 4, 2022 at 10:06 AM.
Reason: typo
As far as I know, G05 isn't the right coolant. Mercedes used MB 325.0 and 326.0 in cars built through April of 2014, and 325.6 and 326.6 in cars built starting in May of 2014. The 325 series is concentrate and 326 is pre-mixed coolant.
As far as I can tell, the early cars use G48 (meets MB325.0), which is blue, and the later ones use may G40, which is pink. Most pink coolants say they meet MB325.5, not .6, so IDK. Fortunately for me mine is early...
Thanks for the heads up, didn't realized there was so much to coolant type! I'll try to look for G48 coolant, though from what I've read, G05 is still compatible though not as good right?
@Mmr1 You are definitely correct in the fact that diesel contains more energy per unit than gasoline. Following your logic, diesel would burn hotter than gas if they’re to burn at the same rate. However, our engines used metered injection both gas and diesel, therefore they do not consumed at the same rate for optimized combustion for the same output in power. This is why Diesel engines in most cases gets better fuel economy. Use less fuel, less heat - like the LED analogy.
Ok, diesel contains 20-25% more energy. The motors either gas or Diesel and it’s oil still need to reach 180f - 190f quickly and stay there! To maintain good oil !
Ok, diesel contains 20-25% more energy. The motors either gas or Diesel and it’s oil still need to reach 180f - 190f quickly and stay there! To maintain good oil !
Nobody is arguing that, yes, diesel engines do need to operate at 180-190F to prevent oil from slugging. The original discussion was if the engine could maintain ideal operating temp at extreme cold (-25C or lower).
Well, here are the result. After the thermostat change, I took the car out for a 150km trip.
In the morning, the outside temp was -27C:
- drove the same highway to work into Edmonton.
- coolant temp was only 60C, all the way 50km travelling consistently at 100km/hr.
I did a bunch of errands in town:
- in the city driving, it the outside temp warmed up a bit to around -21C.
- coolant temp was 70C when moving, and drops down to 60C when stopping.
On my way home, I took one of the major highway 60km (longer to take that route):
- outside temp was -17C
- able to do operating temp at 87C, travelling at 115km/hr.
- once on the highway, I was able to get up to temp within 5mins, car was warm already though.
As suggested by @Mmr1 , oil was changed. Made sure it was MB 229.52 (Quartz Total Inec MC3 5w30 with OEM filter). When I pulled out the oil filter, it was FRAM! I highly doubted that the non-MB dealership that sold us the car would put MB specs oil in there. I also did the fuel fuel. In case anyone was interested, the thermostat that I pulled out was OEM - it also had a slight coat of what looks like corrosion on the top side (I'll grab a pic another time).
Lesson to be learned:
- I need to take the major highway to work in extreme cold, the smaller highway doesn't create enough load for the engine to heat up
- I also need make some sort of cold front cover to limit air flow to the radiator/engine
- I need to finish installing that webasto coolant heater.
- I also need make some sort of cold front cover to limit air flow to the radiator/engine
Ordinarily I would agree 100%, but, I find it interesting that I cannot find any winter covers for sale anywhere. Makes me wonder if something else is going on...
If installing a winter front, be sure it fits correctly on the OUTSIDE of the grill and that it can't work itself loose when driving. Under no circumstances should you block the radiator flow by blocking it under the hood, where it could loosen and work its way into the path of moving parts such as the drivebelt. Bad things will happen.
In such cold temps, I highly advise folks use a fuel additive designed to keep diesel fuel from gelling. The fuel filter heats up fuel that goes back to the tank, but only while the engine is running.
One thing you can try, if you're brave enough, is to shut of the heater. At the temperatures you are experiencing, the heater may be enough to over cool the system. Otherwise, I'd stop fooling around and cover about 80% of the grill. As stated above, block in front of the grill or between the grill and the radiator, not on the engine side.
Not a bad idea. If you have heated seats, crank up to high and turn off all other accessories including the fan itself. As long as no cold air is getting in, you should be keeping warm.
Not sure if the procedure is cover else where already - pretty straight forward as thermostats go, but here it is.
Thermostat Replacement GLK250 BT:
1) remove the “s” air intake pipe by unclipping it.
2) remove the engine cover by turning the lock tab with a screw driver at the front, lift the front and sliding the rear out of the guides.
3) remove the lower front tray from under - 8mm screws. Didn’t count how many though…maybe 10?
4) drain coolant from the LHS corner of the radiator. There’s a twist knob that u turn 180 degrees. I did not do a full drain, only about 4L just not to make a mess.
5) carefully unlock tabs holding the plastic harness tray to gain more access to the thermostat. Pull the tray a few inches higher.
6) disconnect coolant temp sensor, and 2 other connectors that I haven’t paid attention to what they are to allow more room to lift the harness tray.
7) there’s 3 bolts holding the thermostat on the cylinder head (2 on the front, and 1 on the side), remove them. The bolts have metal brackets on them, remember their location. There is also 1 bolt that holds a plastic piece on besides the oil filter cap that will need to be removed. All the bolts were torx, you’ll need either etorx sockets or I just used a 8mm regular socket.
8) pop the wire lock for the upper radiator hose on both ends and remove the hose completely.
9) using whatever pliers or special tool u have to take the tension off the spring hose clamps and remove hose starting with the 2 smaller ones.
10) there are 4 hose connections all together - 2 big and 2 small ones.
11) Install is the reverse of removal pretty much. Be very careful not to snap or crack those brittle plastic electrical connector locking tabs!
12) I refilled the coolant until the reservoir was almost full, then I squeeze the upper coolant hose a few times and got some air out. I also cycled the ignition a few times to get the coolant circulating pump to help me force some air out.
13) I pretty much was able to put the same amount of coolant in as what I took out. Will probably need to drive it in the morning up to temp to fully bleed it.
Thermostat bolts are torqued to 9Nm.
Give me a shout if you have any questions or if I miss something big and my engine will blow up soon!
Thanks buddy. I am going to replace mine since you see improvement on your after the replacement. I may as well flush the coolant as well
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
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