M276 Twin Turbo Coolant Flush DIY How To
06-09-2022, 06:25 PM
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M276 Twin Turbo Coolant Flush DIY How To
There have been a couple of attempts to describe a procedure for doing a coolant flush for the M276 and they seemingly were abandoned mid-stream. As I had believed that I needed to do the coolant on my W166, I share with you all the procedure I used to complete it.
Word of caution: these cars weigh 4900 pounds and are filled with very hot and toxic fluids. Observe every caution and safety protocol. Use safety glasses, rubber gloves and wheel chocks. Be certain the engine is COLD!!
I used 2 gallons (about 9 L) of the purple Si-OAT Coolant from Peak. The OEM was the pink stuff, but some research revealed that the purple is compatible and potentially better. From what I have read, 2015-16 should come with the purple stuff. If you convert, a flush would be a very good idea, rather than mixing. It's not certified by Mercedes however, I believe it to be suitable. Time will tell. I also got 4 gallons (about 18L) of distilled water to flush through the block.
The patient is a 2015 W166.056, US Spec ML400 Sportline. This one is fitted with the M276.821 3.0L DOHC twin-turbo 60-degree V6 (some people call this thing M276 DE30) and a 722.904 transmission. The process for other M276-powered W166, including those branded as GLE, should be identical, except the location of the coolant tank, and that there is just one of those, rather than two, as in this car.
Firstly - park on a flat surface. My car has airmatic so I put the suspension in its highest setting to ease access underneath. I do not believe it is necessary to lift your car. If you do, start with the driver's side as you'll be draining from the passenger side.
There are two coolant tanks and two cooling channels - one is for the engine block, with the second, smaller one for the turbos and intercooler. The one for the turbos is mounted in the Vee, just to the passenger side of the throttle-body and intercooler.
The one for the block is on the driver-side wheel perch, behind the ABS motor (about 3-o'clock in the image above). They are connected via a common pump (which will run after the car is parked), but you won't be able to drain the turbo cooling channel using this method.
If you have the naturally-aspirated version of this engine, the coolant tank is on the passenger side wheel perch, I believe. It's a little easier, as there is only one of them, and not two.
Now is a good time to check that the ENGINE IS COLD. Like COLD-COLD.
Pull out your favorite 8mm socket (I used a 1/4in with a 3 in extension) and unscrew all the screws for the plastic under tray immediately behind the front bumper. It spans the width of the car and is about 10 inches deep. You'll want to at least remove 4 of the 6 screws holding the under-engine tray too (I didn't remove mine entirely because I was lazy and had no issues at all).
Now is a good time to ensure the parking brake is set (it will lock both aft wheels, electrically so it's obvious if it is engaged) and put wheel chocks. Also, have a catch pan (think punch bowl sized) at the ready here. Coolant is toxic. It will kill animals (who evidently love to drink the stuff) and it will make you sick if you touch it too much. Do the best to keep things clean.
From underneath your car, looking up, with your feet pointed in the same direction the car would normally travel, you'll see a 2 inch hose coming from the bottom of the radiator, with a 1 inch hose tee'd off of it. This 1 inch fella is where I drained the coolant as it's easy to get at and will drain fast. There is a metal clamp holing the rubber hose to the fitting - I used a small plumbers wrench (the cheap ones that are about the size of your hand) to loosen that and slide to the side. Using a screw driver, I pryed the hose loose. I was immediately covered in coolant.
I let mine drain out for about 3-4 mins. It goes quick. I got impatient and noticed the hose form the radiator to the block on top of the engine. I disconnected this using a pick tool on the metal collar and poured distilled water in to it. About 2 gallons flushed out the radiator right quick. Another 2 gallon went through the block, but took a bit longer.
I reconnect that 1 inch hose, resecured the clamp and went top side. I filled the cooling system with fresh coolant from the large filler tank. After filling, start the car and run the heater at its highest setting (mine is 84F) with fan set to high. 30 C degree (86F) day, notwithstanding, the heat got to roast-my-face-off temps in about 3-4 mins. Underhood, I can see the tank bubbling, so the car is "burping the system." Turn off the car, and let sit a few mins. Then top off with coolant. My car took 2 full bottles, about 2 gallons (9 ish L).
Overall, the whole process took me a tick more than an hour. Was it worth it? Nope, not with just under 70k mi on the clock. The coolant that came out of it was completely clean, like kool-aid looking-clean. I just didn't have any record that this service had been done before, and took a chance to do it. Peak claims 5 years or 150k mi, so it seems likely that I won't have to do this for a goodly while.
Word of caution: these cars weigh 4900 pounds and are filled with very hot and toxic fluids. Observe every caution and safety protocol. Use safety glasses, rubber gloves and wheel chocks. Be certain the engine is COLD!!
I used 2 gallons (about 9 L) of the purple Si-OAT Coolant from Peak. The OEM was the pink stuff, but some research revealed that the purple is compatible and potentially better. From what I have read, 2015-16 should come with the purple stuff. If you convert, a flush would be a very good idea, rather than mixing. It's not certified by Mercedes however, I believe it to be suitable. Time will tell. I also got 4 gallons (about 18L) of distilled water to flush through the block.
The patient is a 2015 W166.056, US Spec ML400 Sportline. This one is fitted with the M276.821 3.0L DOHC twin-turbo 60-degree V6 (some people call this thing M276 DE30) and a 722.904 transmission. The process for other M276-powered W166, including those branded as GLE, should be identical, except the location of the coolant tank, and that there is just one of those, rather than two, as in this car.
Firstly - park on a flat surface. My car has airmatic so I put the suspension in its highest setting to ease access underneath. I do not believe it is necessary to lift your car. If you do, start with the driver's side as you'll be draining from the passenger side.
There are two coolant tanks and two cooling channels - one is for the engine block, with the second, smaller one for the turbos and intercooler. The one for the turbos is mounted in the Vee, just to the passenger side of the throttle-body and intercooler.
The one for the block is on the driver-side wheel perch, behind the ABS motor (about 3-o'clock in the image above). They are connected via a common pump (which will run after the car is parked), but you won't be able to drain the turbo cooling channel using this method.
If you have the naturally-aspirated version of this engine, the coolant tank is on the passenger side wheel perch, I believe. It's a little easier, as there is only one of them, and not two.
Now is a good time to check that the ENGINE IS COLD. Like COLD-COLD.
Pull out your favorite 8mm socket (I used a 1/4in with a 3 in extension) and unscrew all the screws for the plastic under tray immediately behind the front bumper. It spans the width of the car and is about 10 inches deep. You'll want to at least remove 4 of the 6 screws holding the under-engine tray too (I didn't remove mine entirely because I was lazy and had no issues at all).
Now is a good time to ensure the parking brake is set (it will lock both aft wheels, electrically so it's obvious if it is engaged) and put wheel chocks. Also, have a catch pan (think punch bowl sized) at the ready here. Coolant is toxic. It will kill animals (who evidently love to drink the stuff) and it will make you sick if you touch it too much. Do the best to keep things clean.
From underneath your car, looking up, with your feet pointed in the same direction the car would normally travel, you'll see a 2 inch hose coming from the bottom of the radiator, with a 1 inch hose tee'd off of it. This 1 inch fella is where I drained the coolant as it's easy to get at and will drain fast. There is a metal clamp holing the rubber hose to the fitting - I used a small plumbers wrench (the cheap ones that are about the size of your hand) to loosen that and slide to the side. Using a screw driver, I pryed the hose loose. I was immediately covered in coolant.
I let mine drain out for about 3-4 mins. It goes quick. I got impatient and noticed the hose form the radiator to the block on top of the engine. I disconnected this using a pick tool on the metal collar and poured distilled water in to it. About 2 gallons flushed out the radiator right quick. Another 2 gallon went through the block, but took a bit longer.
I reconnect that 1 inch hose, resecured the clamp and went top side. I filled the cooling system with fresh coolant from the large filler tank. After filling, start the car and run the heater at its highest setting (mine is 84F) with fan set to high. 30 C degree (86F) day, notwithstanding, the heat got to roast-my-face-off temps in about 3-4 mins. Underhood, I can see the tank bubbling, so the car is "burping the system." Turn off the car, and let sit a few mins. Then top off with coolant. My car took 2 full bottles, about 2 gallons (9 ish L).
Overall, the whole process took me a tick more than an hour. Was it worth it? Nope, not with just under 70k mi on the clock. The coolant that came out of it was completely clean, like kool-aid looking-clean. I just didn't have any record that this service had been done before, and took a chance to do it. Peak claims 5 years or 150k mi, so it seems likely that I won't have to do this for a goodly while.
