C350 w204 coolant issues

[M1ckc350]

Hi just bought a c350 cdi w204 and having few issues with coolant circulation.car is not overheating and sits around 90d.coolant pipes are very hard after short drive and alot of presure in expansion tank car has blown top radiator hose of twice..on removing cap no circulation visible.
Any info much appreciated

 

[L John]

90C is not hot enough to boil but that temperature reading is at the sensor (wherever that is), it's likely boiling around the engine causing the pressure.
Jammed mechanical stat, blocked radiator or failed water pump?
The fact you are getting a temperature of 90 leads me to believe water is circulating but not enough.

 

[M1ckc350]

Many thanks Radiator has just been replaced ive just done 900mile round trip to london i thought if was water pump would have surly failed on route maybe not ?.In my experience ive normally seen the circulation of water into most expansion tanks

 

[turbopete]

could be a faulty pressure cap. the hoses should get hard, but not pressurise to the point it blows the hose off!

 

[M1ckc350]

Have seen few posts regarding cap best trying that first before go down water pump and thermostat route.was just on ofchance anyone had same experience

 

[L John]

could be a faulty pressure cap. the hoses should get hard, but not pressurise to the point it blows the hose off!

What temperature should the cap vent at, I'm guessing it's at least 110C.

Note to OP, be very careful when releasing pressure when it's hot and don't release pressure at all if it's very hot.
If the water is over 100C it will not boil when it's under pressure, the cap is designed to release at a set pressure to stop the system pressure getting high enough to do damage to other parts.
If pressure is released at over 100C, the water will boil and expand rapidly and spray boiling water and steam anywhere it can escape.

 

[M1ckc350]

Previous owner had said was fairly new radiator prior to me buying car so im hoping its not anything to do with pressure in cooling system thats done damage to old one.going to pressure test system tommorow and go from their.my first thought was waterpump but circulates when rpm increased to 2000.

 

[hotrodder]

Rad caps vent at a set pressure regardless of temperature

The internet suggests 0005018215 is a part # for various MBs including the w204 and that the pressure relief valve in it opens at ~ 2.0 - 2.1 bar. This is a chunk higher than most cooling systems used to be pressurised to, stuff from the '90s for example would typically have 1.2 - 1.5 bar rad caps for example

Pressure testing the coolant system typically overlooks the cap itself as that's replaced with an adaptor to allow the system to be artifically pressurised. Testing the cap itself needs a different set up but most people probably just replace 'em if suspect as they aren't spendy

How snug a fit is the top rad hose? Longshot but it might be less about the system being over pressurised and more about a top hose that's seen better days?

I wouldn't read too much into the lack of visible circulation in the header tank... they're not supposed to 'see' bulk coolant flow, just allow space for expansion and for the system to self bleed i.e. while the outlet is about 3/4" dia the inlet(s) are typically only 1/4 - 3/8" bore to bleed small amounts of coolant (and any air) from the top of rads etc

 

[M1ckc350]

Top hose seems secure and slots into guide no problem but not impressed with the spring clip fitment.
somethings not right tho even when cars left overnight top and bottom radiator hose still presurised and pressure in header tank.cars only got 66.000

 

[hotrodder]

I forgot they changed to that silly internal hose fitting with spring clips (looks kinda like a half arsed cheapnese version of a wiggins connector). Was thinking the nice simple old way but someone penny pinching by reusing old 'baggy' hoses and/or tired hose clips

Dunno what the reputation of head gaskets on these engines is like but loads of pressure in the cooling system after it's cooled back to ambient suggests something more ominous [/glass half empty]

 

[L John]

Rad caps vent at a set pressure regardless of temperature

Very true, it's just a spring valve but system pressure in normal use is caused by the water trying to boil.
The boiling point of water is directly linked to pressure.

 

[M1ckc350]

Could it be coolant related coolant in header is red or pink cant see that being cause just curious as like mentioned the water is boiling so could it be wrong grade of coolant

 

[hotrodder]

Very true, it's just a spring valve but system pressure in normal use is caused by the water trying to boil.
The boiling point of water is directly linked to pressure.

System pressure in normal use is the result of thermal expansion. Normal running temp for most cars is around 90ish °C and water will only try and boil at that temp if you're at ~ 9500 feet or the pressure is reduced to ~ 10psi

50/50 mix of antifreeze and water has a boiling point of ~ 107°C at standard atmospheric pressure/sea level. Allowing the system to pressurise further raises the boiling point which is useful if you want drive to the alps or get stuck in heavy traffic etc

The origional reasoning behind allowing cooling systems to pressurise was to prevent the loss of coolant after switching off a hot engine (boiling due to heat soak effect). That's still one of the main roles along with helping when idling in heavy traffic etc... when the engine is running at higher rpm coolant in the engine is pressurised by the 'stat restricting flow out while the pump is merrily pumping away. This is what stops localised boiling around the combustion chambers etc

Could it be coolant related coolant in header is red or pink cant see that being cause just curious as like mentioned the water is boiling so could it be wrong grade of coolant

The colour is just a dye and kinda* used to identify the grade/type of corrosion inihibitors in it. Zero effect on boiling temp, that depends on mixture strength but it makes much less difference to boiling point than pressure does

* there are no standards about what flavour should be what colour and the same colour is sometimes used for very different coolants

 

[Steve@Avantgarde]

Sounds like the engine is pressurising somewhere.

3 causes.

1. Blockage in cooling system somewhere.
2. Water pump not circulating the coolant as it should.
3. Blown head gasket(s).

You can do a flow check on the system really easily using a hose pipe. Which will take you about 15 mins. If that is ok then you need to do a block test. You will need a block tester for that, but every good garage should have one.

 

[M1ckc350]

Flow check ? Taking car into garage today to run few checks

 

[Steve@Avantgarde]

Start with the highest entry point and the lowest exit point on the cooling system and then see if the coolant flows. DO the same with the heater matrix.

 

[ioweddie]

Might be the water pump, when I had my c220 it failed, it was made of plastic and a common failure, not sure if yours is the same but worth asking the stealer.

 

[LostKiwi]

That sounds very like a head gasket or cracked head to me I'm afraid.

 

[M1ckc350]

Going to do waterpump and stat to be on safe side new cap ordered cars just done 1000miles to london and back think if was head gasket would have given up on motorway surly Head gasket falure at 66.000 on a merc is very unlikely i hope

 

[star]

Going to do waterpump and stat to be on safe side new cap ordered cars just done 1000miles to london and back think if was head gasket would have given up on motorway surly Head gasket falure at 66.000 on a merc is very unlikely i hope

Good luck with your guess, I'd check the Headgasket/block as Steve suggests before spending money elsewhere.