ianrandom
MB Enthusiast
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- Feb 19, 2010
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- 1986 420SE, 1990 420SEC, 1989 2CV6.
How annoying, especially after all that. I read recently that the magnets in the duovalve assembly can become weak. But if you've replaced the whole lot with new then i guess that doesnt apply.
There is the sensor in the dome light switch area (that little grille) that could be at fault, although i've never heard of that. Or perhaps the fan that pulls the air in through that little grille so the sensor can sample it. (that actually lives down by the glovebox, attached by a tube. You'll hear it whirring if you turn on the ignition.)
And perhaps the dials themselves.
Hopefully your water pump replacement will sort it out for you. Must be freezing up there!
There is the sensor in the dome light switch area (that little grille) that could be at fault, although i've never heard of that. Or perhaps the fan that pulls the air in through that little grille so the sensor can sample it. (that actually lives down by the glovebox, attached by a tube. You'll hear it whirring if you turn on the ignition.)
And perhaps the dials themselves.
Hopefully your water pump replacement will sort it out for you. Must be freezing up there!
Last edited:
ianrandom
MB Enthusiast
- Joined
- Feb 19, 2010
- Messages
- 1,000
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- 1986 420SE, 1990 420SEC, 1989 2CV6.
Did the water pump fix the problem?
Sorry Pete
Active Member
I'm with ianluscombe here, all those routes seem to be the way to go. I'm sure someone will be along to give you a definitive answer soon. Good luck!
Frank O' Phile
Active Member
After warming the engine feel all the hoses for heat. Something must be getting hot.
Maybe check the heater pump? Is it the same as a w124?
Maybe check the heater pump? Is it the same as a w124?
hello all,theres heat in the hose now i flushed the matrix again and got some dirt out of it now i have heat on the drive's side and not the other side.maybe ill have to flush it again with a power hose ? or replace the matrix
ianrandom
MB Enthusiast
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- Feb 19, 2010
- Messages
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- Car
- 1986 420SE, 1990 420SEC, 1989 2CV6.
I expect replacing the matrix is a difficult job. I've heard of using citric acid before. Hopefully that'll help.
Mercedes-Benz sell citric acid for this specific purpose as a service item. But you can buy/use citric acid from anywhere.
You need to flush the system thoroughly before and after (opening all the drain points on the block etc) - you will be very surprised at how much crud is in the coolant system on an old car such as this.
Best of luck and look forward to hearing the outcome.
Will
You need to flush the system thoroughly before and after (opening all the drain points on the block etc) - you will be very surprised at how much crud is in the coolant system on an old car such as this.
Best of luck and look forward to hearing the outcome.
Will
the dirt that came out was light brown came out in wee bits and some big bits ( mosty wee bits)now i have heat on the drivers side and little on the pasagers side ill try flushing it again when i get citric acid ty
I have been through all of this as well - to save typing again , here is a copy/paste of what I posted over on the MBOC forum
I have experienced poor output from the heater on my 500SEL since I got it , and have posted about it on here before .
In my case the coolant temperature is indicated at a 'normal' 80 deg or so regardless of outside temp being in the +20's of high summer or , lately , as low as -13.5 .
Whilst I would not look for additional heat in summer , there has never been a great output from the heater .
I likewise thought an airlock to be the most likely thing and , last summer proceeded to drain down the cooling system . I bought some of Halfords' two stage flushing agent and , after flushing the system through every which way with my garden hose , proceeded to put this through the system . RESULT ! , I thought as I was met with an absolute inferno of heat I had never before experienced in this car , as I ran the car for the required period of time with a mix of water plus the bottle of flushing agent , but with the pressure cap off the expansion chamber . I then drained and refilled with plain water to rinse the system - still roasting hot - before putting the anti reagent in and again running for so many minutes - still HOT . Finally , after all the flushing and rinsing was complete I filled the system with water plus antifreeze - as soon as the antifreeze hit the system - back to lukewarm ??? Not wishing to literally flush £20 odd worth of new antifreeze down the drain I just left it . My heater does at least warm the car up to a nice , toasty warmth - eventually , but it does take a while and the air coming out of the vents never seems particularly hot .
I should mention that while I had the system drained down I also opened up the duovalve and checked it for cleanliness and free movement of the pistons - all seemed fine . The electric circulation pump located next to the duovalve is working as I can hear it running if I turn the ignition on without starting the engine . I got a spare duovalve and pump from another W126 in a breakers yard and will keep these just in case I need them .
So far I have not changed my thermostat as the indicated temp struck me as normal compared to every other Merc I have owned , but I may try this anyway as it is a cheap component .
So , for me it is a continuing mystery too .
I have experienced poor output from the heater on my 500SEL since I got it , and have posted about it on here before .
In my case the coolant temperature is indicated at a 'normal' 80 deg or so regardless of outside temp being in the +20's of high summer or , lately , as low as -13.5 .
Whilst I would not look for additional heat in summer , there has never been a great output from the heater .
I likewise thought an airlock to be the most likely thing and , last summer proceeded to drain down the cooling system . I bought some of Halfords' two stage flushing agent and , after flushing the system through every which way with my garden hose , proceeded to put this through the system . RESULT ! , I thought as I was met with an absolute inferno of heat I had never before experienced in this car , as I ran the car for the required period of time with a mix of water plus the bottle of flushing agent , but with the pressure cap off the expansion chamber . I then drained and refilled with plain water to rinse the system - still roasting hot - before putting the anti reagent in and again running for so many minutes - still HOT . Finally , after all the flushing and rinsing was complete I filled the system with water plus antifreeze - as soon as the antifreeze hit the system - back to lukewarm ??? Not wishing to literally flush £20 odd worth of new antifreeze down the drain I just left it . My heater does at least warm the car up to a nice , toasty warmth - eventually , but it does take a while and the air coming out of the vents never seems particularly hot .
I should mention that while I had the system drained down I also opened up the duovalve and checked it for cleanliness and free movement of the pistons - all seemed fine . The electric circulation pump located next to the duovalve is working as I can hear it running if I turn the ignition on without starting the engine . I got a spare duovalve and pump from another W126 in a breakers yard and will keep these just in case I need them .
So far I have not changed my thermostat as the indicated temp struck me as normal compared to every other Merc I have owned , but I may try this anyway as it is a cheap component .
So , for me it is a continuing mystery too .
It sounds as though you have may have originally had a slight airlock in the system, that was initially cleared by flushing with the hose.
After draining/refilling a few times, you might have re-introduced the airlock again.
The properties of the coolant won't have made a tangible difference in heat output IMHO
Will
Sorry Pete
Active Member
Very odd Pontoneer, though antifreeze isn't as good as plain H2O for heat transfer, I'm surprised you'd be able to detect a difference at the heater vent. Have you got the mixture correct? I'm sure you have, but it's still a little baffling.
The American forum people recommend using Shout laundry detergent to rid the cooling system of oil and literally clean it out before the use of a 10% citric acid solution to descale. I believe that you could use any liquid-style laundry detergent in the UK as long as it's low-suds. Definitely don't use fairy liquid- aside from the corrosion aspect, you'll never get the bubbles out. Also, go easy on the citric acid flush. A guy left it in his 70's 240d for a week to do a 'proper clean', and said he was amazed by the crud that came out. A guy emulated this on his MB and lost a core plug pdq as all that was holding it in was the accumulated scale.
Link here:
Citric Acid Coolant Flush
Post number 9, number 9, number 9
.... has the technique sussed.
The American forum people recommend using Shout laundry detergent to rid the cooling system of oil and literally clean it out before the use of a 10% citric acid solution to descale. I believe that you could use any liquid-style laundry detergent in the UK as long as it's low-suds. Definitely don't use fairy liquid- aside from the corrosion aspect, you'll never get the bubbles out. Also, go easy on the citric acid flush. A guy left it in his 70's 240d for a week to do a 'proper clean', and said he was amazed by the crud that came out. A guy emulated this on his MB and lost a core plug pdq as all that was holding it in was the accumulated scale.
Link here:
Citric Acid Coolant Flush
Post number 9, number 9, number 9
.... has the technique sussed.ianrandom
MB Enthusiast
- Joined
- Feb 19, 2010
- Messages
- 1,000
- Car
- 1986 420SE, 1990 420SEC, 1989 2CV6.
It sounds as though you have may have originally had a slight airlock in the system, that was initially cleared by flushing with the hose.
After draining/refilling a few times, you might have re-introduced the airlock again.
The properties of the coolant won't have made a tangible difference in heat output IMHO
Will
I can't remember the exact figures now , but using the full bottle of Halfords 'Advanced' antifreeze was going to result in a 50:50 mix . I had part filled the system with water , then added the concentrated antifreeze , which was relatively 'gloopy' and took a while to drain into the system from the reservoir , then topped off with water to full and revved fast for a few minutes to try and purge air from the system : as soon as the antifreeze went in the already warm heater seemed to blow cold ( I had the drivers window open when I was doing the job and was monitoring the twmp from the small demister vent next to the window ) . It is quite possible that , due to the thick and 'gloopy' nature of this antifreeze , that air was being trapped in the system again .
Although it was relatively expensive , I was not so keen on the pink Halfords 'advanced gloop' once I saw it go in - I have subsequently found a 5L bottle of Bluecol in my shed , which was the antifreeze I always used to use , so now that winter is once again behind us , I'll finally get that new thermostat and change the coolant again . Also need to do the 280SE as the heater is poor in that one too ( seems to be a common theme with W126's ) .
