Funkwagen

Anyone know how to go about doing this for a w204? My cooling system developed a small leak which is now fixed, but the coolant level got low (warning on dash) and I believe some air got in the system, I want to be sure it's out to prevent any issues down the road with cavitation erosion

Plutoe

On a 272 there is no special coolant system air evacuation process!!

A-drain the radiator!

B-drain the crank case

C-fill at reservoir to correct level and recheck level at running temp!!

Funkwagen

Thanks, just wanted to be sure

Carsy

Funkwagon,

I am always watchful after draining /filling a cooling system. I have had one engine overheat because of air lock in the system but was luckily there was no damage.

This engine also has no bleeding vents screws so air cannot be bled out whilst the engine warms up to operating temps.

During the first start & warm up I monitor the engine temperature closely & gently squeeze the bottom radiator hose. I also do not fill to operating level , leaving the radiator cap off & apply my mouth to the radiator creating a pressure on & off on & off regularly.If the engine temp seems to be heating up & the thermostat has yet to open ( feel the outlet hose return to the radiator ) I switch off the engine to let the heat normalise ( even out )thought out all the head & block & then start again half an hour later going through the same process until the thermostat opens fully . You will have to keep adding coolant through out the process as the air is vented. Monitor the engine temp closely on your first drive.
Use common sense & don't burn yourself in the event of a sudden venting of fluid & air.

c300white

If there is no bleed screw - I would use a vacuum fill tool - or take it to a shop with one and get them to vacuum in the last bit of coolant to make sure no air is in the system - much cheaper than getting the head gasket replaced - or worse ...

95Sinned420

Do it the old way. Fill it up to proper levels, car on driveway with front end higher than rear helps a bit, start the car and let it warm up (heater on high and max temp). Radiator cap off. While its warming up, keep and eye on the temp gauge, give the upper radiator hose a few squeezes while its warming up. Its a good sign if you see the coolant in reservoir go down, it means the system is bleeding itself out. Add to coolant proper levels. Close cap. Stop engine. Let it cool, I usually wait til in the morning. Check levels again, if low, add more. Repeat until you don't see it being low anymore after a cooldown. Normally I only need to top it off once.

Al Golzari

Hi all: I recently replaced the water pump myself on my 2010 C300 (135K miles) and did it before the water pump failed on me. I also replaced the upper and lower hoses (thermostat was changed two years ago by my mechanic). I'm an amateur FYI'er and had a hell of a time bleeding the cooling system at first, but I think I came up with something that works and wanted to pass it along. Instead of buying those kits (which I did but didn't fit on the reservoir cap) and instead of all those YouTube videos where you wait until 2 cycles of the fan going on, etc., this worked the best: Start with your reservoir cap off (of course) and let the car get up to 80 - which is slightly below operating temperature (which as you all know, is usually between 80 and 100). Then turn the car off, wait about two hours, and you'll most likely see the reservoir go down. Fill the reservoir back up to where it should be and repeat the process. You only need to do this maybe 2-3 times until the coolant in the reservoir goes down - and all the air will come out. My heat worked fine and it's been fine ever since.

I didn't have the heater on at all while doing this, I didn't use the kits, I didn't take a long soda bottle, cut the bottom, and turn it upside down, I didn't let the engine run all the way until the fans came on, and repeated that twice, I didn't rev the engine at all, etc. None of that. All of those methods, in some concocted way, simply didn't work for me. The above worked for me and I think it will work for you. I'm not a mechanic so I don't have a vacuum system, etc. Assuming that we're all MB fans on this forum, you know these cars are wonderful but also tempermental (my 5th German car). Maybe those "classic" methods on YouTube work for Japanese and American cars better. But this worked for me - and was the fastest AND gave me the best degree of peace of mind, that all the air was genuinely bled.

Mindlos

Hi... Can anyone help me, my car w204 2014 model had its Thermostat change recently, had a new one fitted in. Lack of knowledge the car wasn't properly bleeded coz it kept using all its coolant. Bleeded the car after finding out how to, engine running, heater on and all that. After 15 to 20 minutes switched it off, try'd to start it again but it wont start. It swings weakly almost like it's gonna start then gose off. Im afraid i feel like I've e blown the top. Can any one help please.

Al Golzari

I'm sorry I can't really help because I don't know what you mean by you're afraid you've "blown the top." I don't understand that phrase. Maybe you got your car fixed by now but was your car really not bleeded correctly in the first place? You said it was "using" coolant. So that would mean that the coolant was going down and you need to fill it up. If your car wasn't properly bled after the thermostat change, you'd have air in the system - the coolant would seem full and you'd be overheating.