No Or Little Heat
 

I have a 2008 GLK 450 and the heat quit working. Here is what I've done and the results.

1. Checked the coolant level - It was full and no leaks were found
2. Checked that the engine gets to operating temp - Runs at 90 degrees C.
3. Felt the inlet and outlet heater hoses - Input hose is hot and the outlet hose is warm
4. Removed the coolant recirculation pump and tested.
a. Used jumper wires to hook the pump up to the battery - pump runs.
b. Attached a hose and put it in a bucket of water and ran the pump - The pump appears to move a sufficient amount of fluid.
5. Checked all the fuses in the vehicle - No blown fuses found
6. Removed the plastic under the dash and watched the servos move the blend doors - It appears that they are all working
7. Jacked up the front end of the vehicle and ran with the radiator cap off to try to remove any air in the system
8. Researched and found that a lot of people say to replace the heater control valve - Called the Mercedes dealer and they say this model does not have one, only the recirculation pump.

The heat will start to blow warmer, I wouldn't say hot, If you accelerate at full throttle and then run about 60 miles per hour. I did this then stopped and found that the outlet hose from the heater core had gotten a lot warmer as well.

Any thoughts would be very much appreciated. I made an appointment to take the car to the dealer but they are backed up and it's going to be a week before they get it in, plus the closest dealer is an hour away and it's pretty cold.

Post your VIN and I will look at the heating sysem

4JGBF71EX8A353597

On an older vehicle, I backflushed the heater core and it totally took care of the same situation you're having. Sediment buildup and also some silicone sealant strands - turns out a mechanic had gotten too generous with the use of the sealant at another point in the coolant system. Backflushing is usually more effective. I used a hose for that, then flushed the tap water out with distilled water.

I did think about flushing it to make sure the flow through it was sufficient.

I'm going to head to the parts store tomorrow and get a flush kit and give it a shot.

Just as a side note, when I did mine (if I remember correctly), I removed the input and output hose where they connected to the engine and used a cheap, plastic barb to pipe fitting to connect the garden hose to the output hose of the heater core. I can't say how easy or hard this will be on your engine, but it was super simple on mine ('98 Suburban diesel). 'Course, I had lot's of room in that big engine bay.

Oh... I remembered something else. I found a bunch of that silicone where the output hose connected back to the engine... or did it connect back to the radiator? Whatever it was, there was a fitting there and the silicone got hung up there.

After a review of your 273.923 heating system, I believe that you either have a faulty front SAM or a faulty controller. This is not a mechanical DIY and you need someone with the electronic diagnostics Xentry to determine the specific fault-----my reason is that you have already checked all the mechanical elements in the system and they are not faulty.

Thank you for the review. I did a little research on the SAM module and it does make sense after looking at some of the other symptoms you can have when it fails. I didn't think much of it, really just thought it was a bad battery in the key fob, but the fob sometimes does not work unless you are close to the vehicle. Other times it works just fine. I will keep my appointment at the dealer and let them know what I've done and ask that they look at that. Thank you again for taking the time to look into my issue.

Hears an update -

Took the GL to the dealership and here is what they suggested
Replace the thermostat, coolant reservoir, and lower radiator hose. They said there is a slight weep from the lower hose and also the tank. They want to replace the thermostat because "this is the first place to start". They said this is just a starting point in narrowing down the issue and it may or may not fix the issue. For $1900 to do this work I would want to know the car was going to be fixed. I told them I was going to think about it and get back with them the next day. When I called back to let them know I was going to come to get the car they advised that their senior tech had looked at it closer (checked the input and output temps of the heater core which were correct, disabled the A/C system to make sure it was not causing an issue, which did not change anything, and checked the operation of the servos in the ductwork). I asked that they pay attention to the SAM module and make sure it was operating normally which they said it was. I guess my next step is to remove the blower motor and get a camera up in there to see if one of the doors came loose and is not moving with the servo unless anyone has a better idea. I did not get to flush the heater core yet due to the extremely cold temperatures we are having but still plan to do that as well.

I TOTALLY agree with your line of thinking regarding the $1,900 as a "starting point" in "hopes" that it fixes it. That small leak has ZERO to do with your issue.

Thanks for the update... still hoping it turns out to be something simple for you!

it is not your thermostat, or tank or hose... unbelievable...

i would start by checking the in / out of your heater core. you either have air in the system and core tends to be a high point and collect air or your core is plugged. if those are correct that heat has to go somewhere- i would check the climate control unit which is integrated into your hvac bezel unit and also trace the ductwork for obstructions/ stuck dampers, etc.