ML 270 CDI - Coolant reservoir (bubbling?)

[Walgus]

Hey guys,
The car overheated the other day to 110-115C but I immediately pulled over when it happened. It was while I was stuck in traffic and the fan had just stopped working a few days earlier so it started to overheat.

Does this movement (video link below) in the coolant reservoir look normal at operating temp? I keep reading on the internet there shouldn't be any movement at all in the coolant reservoir and I'm worried this is actually a sign of a blown head gasket or worse.

 

[oigle]

As fluid expands with heat, you will get some movement in reservoir. Should be fluid though, not air. If air, you do have head gasket problem. Is your cap holding pressure in the system?

 

[Walgus]

As fluid expands with heat, you will get some movement in reservoir. Should be fluid though, not air. If air, you do have head gasket problem. Is your cap holding pressure in the system?

Good question! I don’t remember having changed the radiator cap when I replaced the coolant tank years ago so it might be possible the radiator cap isn’t holding pressure, but to me it looks like air is creating those displacements in the tank.

Worth noting though that I’m not seeing any other symptom that could indicate a head gasket problem, namely white smoke in the exhaust, oil in the coolant tank or milky oil cap.

I’m gonna go ahead and order a new rad cap to see if that makes any difference. Thanks for the input!

 

[mattkh]

Hey guys,
I keep reading on the internet there shouldn't be any movement at all in the coolant reservoir

Movement here is used as an additional confirmation that the water pump is working.

 

[mioba]

Bubbles in tank are either HG leak and/or a cracked head.
You need the gas tested from the coolant to see if its exngine gas,
Check also the circuit very carefully, it could be a pinhole leak somewhere letting in air/fluid out
Are you losing fluid.

 

[LostKiwi]

Run the engine cold and leave 1 minute.
Then whilst still running squeeze the top radiator hose. If it squeezes relatively easily it's fine. If it's rock hard the system is pressurised and has a blown head gasket or cracked head.

 

[Blobcat]

Run the engine cold and leave 1 minute.
Then whilst still running squeeze the top radiator hose. If it squeezes relatively easily it's fine. If it's rock hard the system is pressurised and has a blown head gasket or cracked head.

You can't get hit with a £200 diagnostic fee with advice like that... - won't anyone think of the Mercedes Main Dealers...

 

[tsu]

Hello m8 my ml270 is doing the exact same bubbling with no other symptoms when hitting redline the hoses get a bit stiffer but still easily squeezable. Did you ever get to the bottom of this? Was it head gasket? My thermostat is stuck open btw dunno if it has anything to do with that.

 

[mioba]

Well first things first. If you know the stat has failed - change it then go from there.

 

[oigle]

Hello m8 my ml270 is doing the exact same bubbling with no other symptoms when hitting redline the hoses get a bit stiffer but still easily squeezable. Did you ever get to the bottom of this? Was it head gasket? My thermostat is stuck open btw dunno if it has anything to do with that.

What do you mean by "hitting red line"? Any bubbling pretty much says "head gasket". Running too cold is not good for motor or economy. A steady operating temperature is best, preferably around 83° for that motor.

 

[tsu]

What do you mean by "hitting red line"? Any bubbling pretty much says "head gasket". Running too cold is not good for motor or economy. A steady operating temperature is best, preferably around 83° for that motor.

I mean 100% throttle neutral 5k rpm there is the kind of movement in the coolant that OP shows in his video so I asked if he found the cause to be HG related or just normal function of the water pump. Also i have to drive like a maniac for the temps to get anywhere near 80 so I assume broken thermostat.

 

[ajlsl600]

Good question! I don’t remember having changed the radiator cap when I replaced the coolant tank years ago so it might be possible the radiator cap isn’t holding pressure, but to me it looks like air is creating those displacements in the tank.

Worth noting though that I’m not seeing any other symptom that could indicate a head gasket problem, namely white smoke in the exhaust, oil in the coolant tank or milky oil cap.

I’m gonna go ahead and order a new rad cap to see if that makes any difference. Thanks for the input!

Most likely head gasket. Halfrauds used to do a kit that samples ur rad water for combustion gases. Cud try that also if u can get access to it u can pressurise ur cooling system to rad cap spec if it holds prob but not always an indication that gasket OK. If u go that route Don't pump to over cap spec.
Sykes pick kits used to be able to test cap as well

 

[Doug1234]

To be fair it looks perfectly normal to me , top hose is sending coolant back to header tank and it returns to engine through the bottom one .. if you replace the top pipe with clear hose and lay the hose low so it’s full of fluid and then with engine running lift it up it would catch any air coming from engine in the highest point of hose.
Alternatively fill the header tank up more , just below the cap and then if bubbles come from pipe they will be seen, but my thought is it’s all perfectly normal

 

[oigle]

I mean 100% throttle neutral 5k rpm there is the kind of movement in the coolant that OP shows in his video so I asked if he found the cause to be HG related or just normal function of the water pump. Also i have to drive like a maniac for the temps to get anywhere near 80 so I assume broken thermostat.

Movement in coolant is NOT bubbling. Big difference. Movement is normal. Bubbling is NOT. Get new cap. See if you lose coolant in normal operation. Get thermostat fixed....

 

[horatio]

I’m sure it’s happened to someone somewhere but I have never heard of a HG blowing on an om612/270!