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Can a faulty thermostat cause other issues?

Discussion in 'Electrics, Vacuum, Ignition and ECU' started by X308, Jan 9, 2018.

  1. X308

    X308 Member

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    Your Mercedes:
    w211 2003 2.7cdi
    My mother in laws E270cdi '03 has for some time now been getting the convenience warning, usually rectified following a start within a minute or so.

    As she has stopped driving I have sort of inherited the car pending sale so I have decided to spend a little time doing the odd bits that seem to be an issue.

    Last week I sorted the glow plugs and relay. I also changed the thermostat as the interior dial had been reading 60 degrees rock solid (however accurate that may be?)

    I then had a fiddle with my amp meter pulling a few fuses here and there. Initial inline reading was 2 or three amps with a surge to 10 amps for good measure. Within a minute this had settled to 0.08amp, which whilst slightly high, I thought was OK. The interior (and meter) volt reading was a steady 11.75V rising to 13.8V @ 1200rpm which considering the messing around I had been doing I was not concerned about the voltage, although despite an apparent lack of drain the battery never seemed to get charged fully. There appeared to be no evidence of an unexpected drain.

    Having replaced the thermostat and charged the battery I am now getting 12.3volt rising to 13.8 volts @ 1200rpm. This has been consistent for 5 days.

    Conclusion:

    The lack of temperature in the coolant in turn lead to constant activation of the heater booster (runs off 200amp fuse in right hand footwell (L or RHD)) thus draining the battery to an extent the alternator was unable to rectify.

    From what I can gather the booster is in operation at temperatures under 80 degrees.

    Comments welcome,

    Regards,


    X308
     
    Last edited: Jan 9, 2018
  2. Paul Goff

    Paul Goff Senior Member

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    If I recall my reading of the manual for my car correctly, the heater booster is automatically switched on if the ambient temperature is below 7C AND the coolant is below 70C.
    Even here in Sunny Devon the ambient hasn't been above 7C much recently. So if the coolant has been no higher than 60C then the booster may well have been on all the time!

    All that leaves the alternator with quite a big task, supply 150Amps to the booster, run the car as per normal and charge the battery after a cold start.

    Does the coolant now get fully warm? Mine can take a LOOoong time to get there, even with a fully functioning thermostat(s).
    Try treating the car to a longish drive, say about an hour, see if that helps.
     
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  3. OP
    X308

    X308 Member

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    Hi Paul,

    Thanks for the input - I had 8 degrees and 80 degrees C as my figures for operation. It would be good to see something concrete as to the temperatures of operation and wattage of the element*.

    I can tell when it is working as when it is on, the charge voltage drops by .3V on the incar dial when turning air con off. When turning aircon off and it is not working (ie over 70/80 degrees) the drop in voltage it negligable or at max .1V.

    FWIW I understand the heater output is 1000W or 83 (odd) amps, which is quite a drain!

    The water (according to the gauge) max temp is now 90 degrees C but it does take a good 20 minutes of normal (30 to 50mph) driving to attain.

    Regards,



    X308

    Edit * I cannot see anything in my manual to this effect.
     
    Last edited: Jan 10, 2018
  4. Paul Goff

    Paul Goff Senior Member

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    Just had a look in my Moaners Annual, the figures are below 8C ambient and 70C coolant to make the heater booster operate. I was quoted 1600(?) watts as the power consumption of the booster in by someone on here, in my thread about thermostats etc. Don't know the source, but will look it up.

    I had my booster switched off while having problems with the thermostats on my car, just as well. During warm up it has a large impact on fuel consumption during warm up. While I had stat problems it would have been most of the time!
     
    Last edited: Jan 10, 2018
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  5. Paul Goff

    Paul Goff Senior Member

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    Had a look at my thermostats thread, someone says the booster is 1700 watts, that's nearly 2.5 BHP, little wonder it has a negative impact on diesel consumption!
     
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  6. OP
    X308

    X308 Member

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    I have read that too....

    And THIS says 1000w.

    Not sure if this is a MY difference, a differece or no difference. Some clarity would be nice.

    Regards,


    X308
     
    Last edited: Jan 10, 2018
  7. Botus

    Botus Senior Member

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    two thoughts / questions....

    this is tractors only ? (not petrol)
    this is not UK spec ?
     
  8. OP
    X308

    X308 Member

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    Yes, the diesels take a long time to warm up to a sufficient temperature to warm the cabin. A heater booster is placed in the intake to provide an electrically generated heat until the engine reaches it running temperature. The electric heater works off certain other perameters such as battery charge and external temperature.
    You can test the operation by pressing the "Rest" button on the HVAC, without inserting key.
    When engine is running if the perameters activate the heater it can be turned off by disabling air con. The heater is amp-heavy. (Obviously)
    AFAIK, it is standard on UK W211 "tractors"

    Regards,


    x308
     
    Last edited: Jan 11, 2018
  9. Paul Goff

    Paul Goff Senior Member

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    According to my owners manual the booster is only on disiesel models of my car.
     
  10. Paul Goff

    Paul Goff Senior Member

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    Interesting, the booster
    Interesting, on my car the booster is plumbed into the part of the coolant circuit which feeds the heater matrix, so clearly some differences then!
     
  11. Arudge

    Arudge Senior Member

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    Just to throw a spanner in the works, the output voltage from the alternator seems too low. I'd expect 14.4 v @ 1200 rpm.
     
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  12. OP
    X308

    X308 Member

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    I am referring to the Heater Booster (PTC). You may be meaning block heater?

    I am inclined to agree on this one. The max I can get on the in car gauge is 13.9V. :(

    Regards,


    X308
     
    Last edited: Jan 11, 2018
  13. Arudge

    Arudge Senior Member

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    This may be just a poor connection. At the rear of the alternator there's a small plug with a single wire. (not the big cable that bolts on) Pull the plug off and test the voltage there, you should have full battery voltage with the ignition on. If you have full voltage clean the plug and the socket as best you can because they can go a bit manky, and the voltage is not making it to the other side of the plug, which is the problem i had. It's preferable to test the other side of the plug to make sure you a good connection with the plug, but that means taking the back off the alternator. If you haven't then you've got some tracing to do. In short, if you have low voltage here (i certainly had) you'll have poor charge voltage at the battery, and with poor battery voltage comes a lot of strange goings on. Which you also have.

    You should be getting full charge voltage at idle, you have nothing. 11.75v is just the battery voltage and that's poor as it is. A fully charged new battery, at rest with no drain or incoming charge should show 13.6v.
     
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  14. Paul Goff

    Paul Goff Senior Member

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    It's referred to in my owners manual as the Heater Booster and has the same name in the workshop manual schematic of the cooling system. Mine does seem to be unusual though, it has a fuel heater/cooler and associated auxiliary radiator + thermostat.
    According to my local MB dealer my car does not have any of this! ;-)
     
  15. LostKiwi

    LostKiwi Senior Member

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    If you have a DPF a failed thermostat can prevent a regen causing it to block.
    Something to beware of.
     
  16. Botus

    Botus Senior Member

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    Thanks, never knew that.

    So all model year 211's ?
    and if the rest bit is "broken" this doesn't work ?

    On BM's its normal rest is broken as no one ever pressed the button in last 10 years....
    need to check my fathers 211 and my 221 to see if rest does anything
     
  17. OP
    X308

    X308 Member

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    @Botus

    I have only had a W211 for a week. Ask me a question on Volvos Jags or Audi and I am your man!

    AFAIK, the rest button is applicable to W211 with (optional) 4 Zone Thermo...whatever it is called. The HVAC should have a digital reader I think.

    If you have a rest button, then I expect it should work.

    The heater booster should operate with the engine running, not on reserve, voltage within range, with the ambient temp lower than 8 degrees and air con in operation.
    It can be turned off if the perameters meet this specification by turning the air conditioning off. My in car volt meter drops by .3V when the booster is working.
    The theory is that without a key in the ignition, if you press the air con/rest button the car interior should heat up.
    If the button is pressed for around 5 seconds with engine running there is an interesting diagnostic feature.

    The blower is fused from the front pre fuse box and will probably be iro 200AMP!!

    I am going to have a look at the starter motor tomorrow and can take some picks and readings if this may help you?

    Regards,



    X308
     
    Last edited: Jan 12, 2018
  18. OP
    X308

    X308 Member

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    @Arudge

    Thanks for your advice. I will have a look underneath. I hope it can be accessed from below as I don't fancy taking the alternator out.
    Incidently the 270 had a 120 AMP alternator? Is that considered decent?

    I get 13.9 with air con, lights and radio on @ 1200rpm. With the heater boost on I get 13.6 under similar conditions.

    In pos 1 12.4V, pos 11 12.2V and on cranking 10.4V. It has been a week since I last charged the battery. Bosch S5 019 013.

    Regards,



    X308
     
  19. Arudge

    Arudge Senior Member

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    The size of the output is designed to supply adequate power with everything switched on as not to draw anything from the battery with the engine running. In essence, the battery is only there to start the car and power accessory's when the ignition is off. I use my REST button a lot, usually waiting for the daughter!

    Mine's only a 90AMP but i don't have water heaters, you do. With reduced voltage comes reduced power to your heaters, which isn't helping your situation.

    You readings are still low imo. But for the sake of the exercise i will do exactly as you have tomorrow and give you the readings.
     
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  20. LostKiwi

    LostKiwi Senior Member

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    The Rest function is present on most MBs as standard. All 4 I've had have had the functionality.
    Basically it's function is to provide heat to the cabin when the vehicles engine is no longer running. It does this by using a small electric pump to circulate coolant water through the heater matrix. There is no additional heat source.
    Similarly it can blow ambient temperature aid around the cabin in hot weather ( if the Aircon has been running it will provide limited cooling until the evaporator warms to ambient.
    If the Rest function doesn't work the most likely cause is failure of the electric pump.
     

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