bleeding the cooling system

[fred_raven]

As many of you will know - have had problems ( now fixed ) with the duovalve - just had to have the water pump replaced - now also fine - EXCEPT - cant get any heat from the heater - obviously an air blockage - tried squeezing the pipes - drove it around 400 mls yesterday - still no water in heater - any bright ideas PLEASE

 

[Mercedes cozy]

Is the thermostat ok. Try and replace it as this is one of the cheapest things to buy and replace.

 

[Brian WH]

As many of you will know - have had problems ( now fixed ) with the duovalve - just had to have the water pump replaced - now also fine - EXCEPT - cant get any heat from the heater - obviously an air blockage - tried squeezing the pipes - drove it around 400 mls yesterday - still no water in heater - any bright ideas PLEASE

Usually works if you take the radiator cap off, put heater in full heat, with fan on and start the car. Run for 5 minutes and squeeze pipes to heater and header tank. If water level has dropped then you are winning. check heater output, if OK put radiator cap on again and should be OK. If above works take car for 10 mile run with heater on full and it will help to finalise circulation.

Don't forget to top up the coolant afterwards.

Let us know how you get on.

 

[Ian B Walker]

You may have a seperate water pump for the heater. On some Duovalves it is a cylindrical unit actually attatched to the valve. On others it is a seperate valve / pump attached to the same line. Check to make sure it has power and that it works.

 

[fred_raven]

tks Brian and Ian , tried that - did also think of the pump Ian , but checked it this morning and can feel it working. Ran car got some heat from heater but then went cool again

Am sure its JUST a B****y airlock - just cant seem to shift it though

 

[Ian B Walker]

Ok have you tried undoing the hose to the heater from the cylinder head and pouring coolant into it till coolant pours out of the heater?

 

[fred_raven]

tks again Ian - havent - yet , but think / hope i may be getting somewhere - its ticking over now and seems to be improving - watch this space

 

[fred_raven]

NO - now warm but not hot. Pipes going from duovalve to heater still only just warm to the touch. I assume water flows through the duovalve to the heater then back to the cylinder head. Is this correct? strangely the bypass pipe going back to the duovalves is hot ! Is this just coming straight back from the cylinder head ?

If this assumption is correct could i just remove the outlet pipe at the far side of the heater till coolant flows out ( from the heater ( presumably will have to block the pipe form the cylinder head to stop all coolant gushing out !

 

[Ian B Walker]

On some models the pipe from the Cyl Head to the heater are split half way. If you were to uncouple this split (assuming you have one) and pour coolant into the Cyl Head end till coolant flowed out of the heater it could solve your problem. However, you say that the pipes from the Duo valve are just warm. Are they working correctly? I know its a daft idea, but have you checked the fuses?

 

[fred_raven]

pretty sure the duovalves are ok - i have tried disconnecting connection - default i believe is fully open so should be the same as max heat ! If i disconnected at split pint by cylinder head and poured in coolant , where would it come out - at the duovalve side of the heater? would thie same result be achieved by letting the pump force the coolant through the duovalves and heater with this split undone?

 

[Ian B Walker]

I dont think that the heater pump has enough power to remove an air lock, I may be wrong and someone will come along and tell me The heater it the highest point in the cooling system and as we know air will seek that out. If you have two open ends in a circuit and fill one end, then the other free end will expell air / water etc. Sorry if I may be missleading you by my poor description.

http://www.detali.ru/cat/oem_mb2.as...GM=717.433&CT=F&cat=506&SID=83&SGR=180&SGN=04

Item 11 should be a split

 

[fred_raven]

i do understand what you are saying - but without taking the duovalves apart - cant see how i can get both sides open - not sure how to undo connections on the bottom of the duovalve - my thoughts were if i split at the joint the pump would only have to push the collant against air ( thats trapped ) . My cvoncern is if i do split at this point even without engine running will coolant from cylinder head gush out - Must have car available for 6 am tomorrow !

 

[Ian B Walker]

see my edit.

 

[fred_raven]

latest drivle on this - disconnected by pass line from duovalve - thought the pump might push water thro - Ian was right , it didnt. decided to take top of valve off again . Strangely even then with top off and ign fully on so pump was working no major flow of water. Any way despite being assured by swmbo that dinner was ages away had the call for " meal going on table ". reassembled . Yesterday went out bright and early ( work ) driving along about 12 - 14 deg and lo and behold heat from both sides ( a/c doing exactly as it should) dropped passenger at Luton - went to wards heathrow , stopped at Uxbridge for brekky. After being fed decided to check coolant level - had dropped - expected this. filled it up. any way - last night on way home guess what - heat from left COLD from right . then heat from left went - checked level - needed topping up when done heat from left again. so far none from right . Suppose progress is being made - but boy is it difficult.
One thing i am unsure of is even when engine is fully at temp if i remove cap on expansion tank i only get a slight hiss. should this not be pressurised .

 

[fred_raven]

here's the latest - having seen Big x link to MBBraingears noticed the flow is reverse of my assumption. coolant flows through the heater and out thro the duovalves. any way eventually get water thro the heater ,( several times - last time by removing clips at bottom of duovalve and running engine till coolant came out both pipes ) But it aint staying there !!!! am now wondering if there is a leak - is losing some fluid , have noticed that there is a hissing sound at the duovalves when the engine is turned off - is it sucking in air ??

 

[fred_raven]

duovalve !

A final post on this ( i hope ) yesterday go to the end of my tether with this and removed one of the cones from the valve - result instant heat. so the problem was with the duovalve - wasnt opening . However when i took it apart trying to sort this out it did operate, I think the problem was the seal at the bottom had perished and expanded so that if the valve was in the open or closed position it was always closed. drove to MB collingwood ( only people with one in stock) changed and now hot or cold as i desire.
Only down side £175 to cure what replacing 2 rubber washers could have achieved if the damn thing had been designed to be servicable.

As an asside was about to bin the old one - but decided not to - if anyone has need for it - top half perfectly servicable - solenoids and plungers all working fine .

What will i do with all my spare time now !!:bannana: :bannana: :bannana: