Overheating

Discussion in 'Tech/Mech General' started by John & Joan, Aug 22, 2013.

  1. John & Joan

    John & Joan Funster

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    I have the S700 Hymer on the Mercedes 410D 1992 chassis. It is overheating when pulling up hills.
    I was using about a litre of water every time I checked the radiator.
    I had it in for a service this week and the radiator has been drained and flushed. It was then pressure tested and a small weep of coolant was coming out of the bottom hose. The hoses have been taken off and cleaned and retightened. The system was retested and no leaks.
    Yesterday I went for a test run and the temp gauge still rose to almost the top of the gauge on steep long climbs.
    I did notice the fan was not cutting in as it used to do. Much shorter run only when the temperature was well into the top segment of the gauge. It used to cut in at a lot lower temperature.
    The fan is a viscous fan coupled to the fan belt and running continuously. However on reading the handbook it has a clutch system filled with silicone operated by a bi-metal strip.
    When the engine is cold the clutch is disengaged and spins at about 1000rpm. When the engine reaches 85c the bi-metal strip expands and the clutch engages and the fan now runs at same speed as the engine.
    At 21 years I wonder if this clutch is wearing out and that is the cause of the problem. It was noticeable when the fan cut in but we are now noticing that this is not so frequent as it was even earlier this year.
    I have also noticed that the temperature is varying considerably. With the interior heater fan on full and the radiator fan cutting in the temperature drops very quickly from near the top of the gauge to almost bottom (below the first mark) almost to the thick cold mark.
    The gauge is divided into thirds and the pointer normally stays in the lower to centre area. The only time I have noticed it going above this before was on the long slow pull over the border into Spain from France fully loaded and towing a Smart Car on a Trailer. The current problem is even when the van is solo and lighter loaded.
    We have had problems a couple of times with the fan belt tensioner. We had a new one fitted in Spain last winter at a Mercedes dealership.
    Has anyone any experience of problems with these fans?
     
  2. TheBig1

    TheBig1 Funster Life Member

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    sounds like a faulty thermostat to me
     
  3. Snowbird

    Snowbird Funster Life Member

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    John. I had the same problem with the same chassis. After fitting twin 12 volt fans, a new radiator, new thermostat it was the viscose fan clutch not coming in sometimes. You can engage it permanently as a get you home measure and that will prove it. Mine ran fine on the flat and just started going up on long pulls or when pushing it down the motorway. Its fine since fitting a new fan clutch.
     
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  4. vwalan

    vwalan Funster

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    think dave is right . thats what i would go for .
     
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  5. DP_JAY

    DP_JAY Funster Life Member

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    When I've had that problem with an Iveco it was the rdiator core "furred up" on the inside.
    New rad fixed it.
     
  6. rainbow chasers

    rainbow chasers Read Only Funster

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    It will definitely be the fan - I would replace thermo and temp sensor while you are at it if you are touring as these are all cheap and consumable items.

    If loaded and towing, I would look at getting an auxilary fan that you can put in front of the rad to aid cooling.
     
  7. John & Joan

    John & Joan Funster

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    Just been onto the local Mercedes Truck Dealer. The engine is a 602.904 type. There is only 1 fan and thermostat listed for this engine.

    Viscous Fan £125 + Vat (Not held in stock but obtainable by Wed/Thursday from Germany) Delay due to bank holiday.
    Thermostat £16.90 + Vat

    There should be an audible whoosh when the fan cuts from standby (idle speed 1000rpm) to being powered by the engine. The fan cuts in as the engine heats up above working temperature and switches back to standby as the temperature drops.
     
  8. Snowbird

    Snowbird Funster Life Member

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    I did not pay that much, it came same day to my mechanic. I have tried calling him this morning to find out where he got it but no answer. Will try again later.
     
  9. Johns_Cross_Motorhomes

    Johns_Cross_Motorhomes Trader - Motorhome & Accessory Sales

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    as snowbird said, there's a manual/ get you home lock on the viscous fan hub. If you look at the actual finned alluminium part of the hub, there's a hole tapped 8mm, you wind a bolt in, and that locks the hub. You'll probably need a mirror to find it, I can't remember now if it's on the front or back face:Doh:. This is a 'permanent' or one way fix, as once the bolts been wound in, the clutch'll never slip again, even if you take the bolt out!
    With the hub locked, the fans going to be working at full torque all the time, so as we say, just a get you home fix really.
    I'd try a few motor factors for the viscous hub before committing to maindealer prices.
     
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  10. Sundowners

    Sundowners Funster Life Member

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    I do agree with the others---definitely lock the viscous unit first------it is a pity that you can't unlock though:Sad:--------best to be sure of the 'fault' before dumping loads of cash on it-------------------there are several things that it could be-------------------but as you have noticed a difference in the way the fan is running--I would start there:Smile:
    Nigel & Pamala
     
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  11. Snowbird

    Snowbird Funster Life Member

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    It seems there was two sizes of fan clutch fitted, one is larger than the other. Make sure which one it is before ordering. Sometimes but NOT always there is some play in the fan when the clutch has gone. Your symptoms are EXACTLY the same as mine. It gradually ran hotter over a period of 3 months. If I eased of the pedal when the temp was rising, it would slowly fall. When cruising it ran at normal but when climbing or running above 60 on the motorway it gradually got hotter. Once I had got to the top of the hill and eased off, the temp came right down almost to cold. I flushed the rad, no difference. I fitted a new rad, no difference, I fitted twin 12 volt fans, no difference. I checked the thermostat in hot water, no difference. I fitted a new thermostat and fan clutch, BINGO. I wish you had posted this problem before me. It would have saved me a lot of stress, work and cash.
     
  12. Terence

    Terence Read Only Funster

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    Overheating Mercedes D410

    Hi all,
    I have owned my van for 12 years and it has 160.000 miles on the clock. I think the big temperature swings are a design characteristic of this vehicle. My temperature will sit at about 80 degrees whilst not working to hard. Long hard pull over the Pyranees etc will raise the temperature gauge to about 95 degrees at which point the fan will kick in and the temperature gauge will drop back below normal, the fan cuts out and the cycle starts again. There was at time when the temperature gauge was reaching 100 degrees before the fan cut in. My solution was to fit a new thermostat and reverse flush the radiator. All went back to normal the fan kicking in when the vehicle is working hard. These are just my own thoughts I may well be wrong.

    Terence
     
  13. Chris

    Chris Funster Life Member

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    My old Vauxhall Chevette used to overheat all the time .

    Had to have the heater on full in the summer to cool the engine.

    Being an engine numpty I didn't consider clutch fans, thermostats or anything else.

    I just concluded the car was a bag of sh*t.

    And I was right:thumb:
     
  14. John & Joan

    John & Joan Funster

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    We have had the Hymer S700 since 2006 and this problem only started at the beginning of August. Running over the same hills to and from the south lakes it never got this hot even towing the car on the trailer and fully loaded up.

    Running light it still rises.

    Ordered the new fan and thermostat so that should fix things.

    We head for Spain in the winter so want a reliable set up.
     

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