Agreed. I can quickly remove and put back that cover in about 30 sec and I usually do that when I see -20C or below in the forecast. I don't do much highway driving now due to working from home either.

Side question: I don't remember if tranny cooler is integrated into the main radiator or has its own front-mounted radiator on GLK?

 

Trans cooler is a front-mounted part.

 

This is what control the vacuum line of the coolant pump.

Switchover valve for coolant pump (Y133)
The switchover valve is located at the front of the
engine, on the left of the throttle valve actuator.
The position of the regulating valve (open or closed) in
the coolant pump is controlled by the switchover valve
of the coolant pump. When the regulating valve is
open, the coolant can circulate in the coolant circuit.
In the rest position, the regulating valve is open.
The coolant pump is switched off during a cold start
for max of 500 s if the following conditions are fulfilled:
• The limit values stored in the control unit for intake
air and coolant temperature and for the total fuel
injection quantity have not yet been reached.
• The engine speed or injection quantity has not
exceeded the specified limit value.
• "Heat" has not been requested by the automatic air
conditioning control and operating unit.
Sorry I don't have a part no to hand. A fault in any electrical circuitry would be flagged as a fault code but a vacuum failure would not unless there was a vacuum transducer monitoring it.

 

@KTM530 Thank you for this ^^
I had to replace one in 2019... Not sure what happened to the pump but it was during one of those "-30C outside weeks" in Calgary and I noticed the coolant was below level in the expansion tank after CEL came on. Water pump didn't leak externally though. I did notice dried coolant traces around the switchover valve and wastegate control pressure transducer. Here you go:


Code was P226100 - "The bypass flap 'Charge air' has a mechanical malfunction." and P0299FB - "The boost pressure of turbocharger 1 is too low." Both flaps operate via vacuum so I started tracing it and found the switchover valve above full of coolant and shot. NO electrical signal output either. Replaced it - both codes went away. Been checking the vacuum system and water pump regularly since then - no traces of coolant present, vacuum reservoir is empty, no external leaks around the water pump too. I am going to test the water pump again and see if it still holds vacuum (according to forums original one has a plastic impeller and is prone to fail).

I am attaching CELs list that is common for vacuum/coolant issues and vacuum diagram for OM651, hope it helps someone.

 

I don't want to hijack the thread, but, since the OP has a lot of cold weather experience, I figured I'd ask...

Yesterday morning it was -15F here (-26C). I've always been concerned that mine cranks slowly, but it has always started, and the battery has always tested good, until yesterday...

It cranked very slowly, maybe estimated 60 RPM (2 compression strokes per second.) It did not start, but it also did not grind to a halt. I quit because I didn't want to kill the battery in case I had to leave it for a few days. AAA came and put a jump box on it and it started instantly.

So, I guess my question is, what is normal cranking speed? Is there a speed below which it will not deliver fuel? I suspect I need a new battery, but I'm wondering if maybe the starter could be weak, too. Snowing like crazy now, but I guess the next step is to take the battery out and charge and test it, again...

TIA

We now return you to our regularly scheduled programming...

 

Your issue is most likely a weak battery if jumping it started right away….(unless AAA used 24v to jump).

Back to temperature….I tested the vacuum line on the water pump, holds vacuum. The pneumatic solenoid opens briefly after cold start. I think the EGR contributes to the warming up of the engine for stock tune as pointed out earlier.

 

How fast would you estimate your engine cranks on a "normal" day? On a really cold day? Can you (like I) count the cylinders easily?

 

If I had to guess, around 1s of cranking no matter what temperature is outside. Mine seems to start easily...just idles a bit rough since the tune in the cold, but never dies. I'm not able to tell how many cylinders are contributing/not firing.

I left my scanner at work, but when I get a chance to grab it back later this week, I'll hook up and give you my cranking rpm.

 

That's kinda odd. My wife has experienced something similar in cold weather where it seemed that car will not start but it did. I think we replaced the battery and it's been fine (but we don't get very cold days).
With weak battery what normally happens is it just won't do anything. If there is not enough voltage it just won't crank at all...that's when you know you need a new battery. They are only good for 5 years.

 

Yeah, that's why I haven't just run out and gotten a replacement. Usually, with a weak battery, if it cranks at all, it slows down pretty quick and stops all together, followed by a series of death throws from the starter solenoid. I actually was able to crank it for probably a total of a minute with minimal slowing, but, since it didn't start, I decided to quit because I didn't want to have to leave it where it was with a stone dead battery.

On the other side of the coin, it did fire right off with the jump box. I wish I knew if there was anything special about that box...

I've always (since last spring) thought it cranked rather slowly, but, as I said, I had the battery tested and it checked OK, and it's always started within a couple of seconds, until the other day, which was by far the coldest I've seen since I got the car.

I didn't want to hijack this thread, so, maybe the moderators could move these posts to a separate thread?

 

I can be making stuff up as all this is beyond my knowledge but maybe voltage wss still ok but the cranking amps were not in such cold.

 

Yeah, unfortunately, the volts and the amps are directly proportional to each other...

 

Oh you have 250 diesel? Probably has its own cold weather starting issues. Mine is m272 so no high pressure pumps or auto stop/start. Only early 2000s tech.

 

Hijack alert... I started a separate thread here.

 

Think of it this way: The idea behind an internal combustion engine is to convert chemical energy into mechanical energy. Heat energy is an unwanted byproduct. (Except in winter!) Any heat produced as a result of the combustion is "wasted" energy.

Diesel fuel does contain more available chemical energy than an equal volume of gasoline, but the difference is not nearly as much as I always thought it was. Someone pointed out to me a while back that the difference is only about 5%. But a diesel engine uses about 40% less fuel to produce the same power output as a gasoline engine with the same number of cylinders and total displacement. More mechanical energy from the same amount of fuel means less heat, since the chemical energy you've spent has to accounted for and the equation balanced. If it's not power, it must be heat! A major reason that a diesel engine is so much more efficient is the extremely high compression ratio. There is a lot more oxygen crammed into the cylinder at the top of the compression stroke, so the fuel is able to burn more thoroughly. A diesel engine is able to accomplish this because the fuel is not injected until the piston reaches the top of the compression stroke. It is only compressing air, not fuel. A gasoline engine compresses the fuel/air mix, so the compression ratio is limited by the fuel's ability to avoid self detonation, or "pre-ignition." (That's the "pinging" a gas motor makes when the octane is too low, or something else goes wrong.) By the way, many manufacturers are currently working on Direct Injection designs for gasoline engines which will greatly increase their efficiency and improve their emissions performance.

Both gasoline and diesel engines like to be "hot" in order to work efficiently. But with a gasoline engine the problem is "How do I get rid of all the EXCESS heat the engine produces?" With a diesel, the problem is just the opposite: "How do I conserve heat in the engine so that the fuel burns more completely?" On a cold day there's hardly any coolant circulating through your TDI, and the cooling fans will never even turn on! The problem of conserving heat also partially explains why the fuel mileage drops so much in the winter. ("Winterized" fuels containing less energy are also a problem.)

The "clattering" sound of a diesel has nothing to do with the amount of heat produced. A gasoline engine is burning fuel vapor mixed with air. A "flame front" moves outward from the spark plug. It is more of a rapid, smooth burn than an explosion. A diesel engine, on the other hand, burns very finely atomized droplets of liquid fuel. Ideally it would begin to burn instantaneously as it enters the combustion chamber from the nozzle of the injector, but in practice there is always a little bit of "delay" and a tendency for the fuel to explode all at once. Hence the "clatter" you hear. Many diesels, including TDIs, use Pilot Injection to help control the combustion noise. A tiny, metered quantity of fuel is injected several degrees before top dead center in order to start an "early" burn which helps ignite the main injection more rapidly. That also helps lower emissions. The new HEUI injector designs (High efficiency Electronically controlled Unit Injectors) use extremely high fuel pressures (about 10 times higher than most DI diesels)to more precisely meter the pilot injection, and to more thoroughly atomize the fuel spray for more efficient combustion. More complete burning means more power from less fuel, accompanied by lower emissions.

 

Add me to the cold engine temp club... So here are the details and I actually think the engine just got cold.

2015 GLK 250 with about 48k miles. According to the dealer it recently had the coolant and oil changed as part of a major service. The engine typically gets up to operating temperate within 15 minutes even driving at slow speeds with freezing temperatures.

Yesterday I had been driving for about an hour at highway speeds with outside temperatures around 25F-35F degrees and no engine temperature fluctuations. Once I got off the highway I was on some back roads going up into some mountains so the outside temperature dropped to about 10F. Af one point I was going down hill on icy roads, so about 15-20 mph and that is when the engine temperature dropped below 80c. It took about 20 minutes for this to happen but it happened. The road I was driving on turned out to be closed, so I turned around and drove back up hill in the same outside temperature. The engine temperature bounced back to the normal range almost immediately and I never saw the issue again.

Going down hill my engine was just barely above idle but coasting at about 20 mph, so no power with a decent amount of airflow. After I turned around the RPMs were around 1,500-2,000 as I drove up hill going about the same speed.

My theory? The thermostat works just fine but eventually the air passing through the engine compartment got so cold that it cooled the engine block. I have never seen this happen just idling or driving under any load.

 

The heater core is more radiator than you need under those circumstances. Mercedes sacrifices engine temperature for passenger comfort.

 

Diesels cooling systems operate at similar temps. Both engines need about 190f.

There are 3 air intakes, the grill, the two 6” square holes to each side of the license plate and the bottom chrome piece. I blocked off the bottom two and it warmed up in 9 minutes at 30f vs 13minutes. I screwed on a thin piece of black foam board on each side of the license plate ( an art supply shop should carry it) and I used 2” drywall screws, because that’s the shortest I have and nothing is in the way to hit, and I used the real aluminum duct tape. ( I’ll worry about removal when it’s warm). I Drove 75 mph and it all stayed on and vehicle is much warmer without all that extra air cooling it.

About 66% air blocked off


Black 1/4” foam board slipped behind license plate and two screws used through the plastic .

 

Yes mb doesn’t advise grill covers , or checking your transmission fluid , or getting your local mechanic to keep your repairs low. Yes a grill cover needs intelligence to monitor. But remember, the Glk or any mb can run in the Arabian desert at 125f , at 90 mph , with ac on safely . It’s about 5x oversized for 32f

 

I thought about this and did an experiment today and guess what, @John CC is 100% correct! It is 13F out today and I was driving around town with the heater on. My engine temperature never reached the 80 degree mark, so I turned on the heated seats and turned the heat completely off, within 2 minutes the temperature went right up to just above the 80 mark. A couple of lights later I turned the heat back on and it fell below 80 again.

It appears that if it is really cold out the heater can cool the engine to below normal operating temperature...Crazy...

 

Funny I noticed exactly the same thing this weekend where the temp would go under 80 with full heat and low engine load.

 

I think the trick is not to have the heating system on AUTO and keep the fan speed at a lower speed. The temperature of the heat will be higher and the engine will reach operating temperature...

 

It’s called a bad thermostat, it fails to properly modulate the engine temperature by fully closing , it’s opening early. Or the fan is running. From what I see here Glk thermostats fail early. A cold motor ruins motor oil and sludges the motor. The Glk is complex, you don’t want sludge.

 

As you pointed out, it’s a complex system, it is not always just the thermostat! I’ve changed thermostat and the temp behaved exactly the same. Also confirmed that the vacuum system, solenoid and water pump is working properly.
There is an inherent design flaw here with the OM651 in winter operations.

 

Here are three reasons why I don't think my thermostat is bad:

* If I am not mistaken the heat runs directly off the engine block and is not in the loop with the radiator / thermostat. My radiator can be ice cold and the heater blows hot. If the thermostat was stuck open I would not have heat until the entire radiator loop heated up.

* If the thermostat was stuck open, then I would be able to freeze the engine at highways speeds in very low temperatures. Last night I drove in 5F degree weather at 75mph for 45 minutes. At highway speed there is enough heat being generated that the temperature gets to normal and stays there very quickly. It is only under light load with the heat/fan on high that you can cool the engine in very low temperatures.

* The engine warms up very quickly (5-10 minutes depending on load) and the radiator stays cold until I drive for a good amount of time.

I think the GLK just has a large enough set of heater coils that under very low temperatures with a light load have enough cooling to drop the engine temperature... Nothing to worry about and not necessarily bad...