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Thread: Defender TD5 Coolant Loss When Cold

  1. #1
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    Defender TD5 Coolant Loss When Cold

    Hey,

    As the title states, my 1999 Defender TD5 is currently having an on again/off again issue with coolant loss when cold. It doesn't always leak and I drove at night and day time, shift worker. When I go to drive for the first time of the day, I check the coolant and find that it may be low so I fill to the cold level (sometimes its not much). I can drive around all day and there is no loss and no signs of loss. I have a temperature sensor and a low coolant alarm fitted which has shown the engine has never gotten too hot or lost any coolant. When the engine cools down several hours later (talking 4 or more), I can find either a small, large or no coolant puddle under the front on the ground. The top hose is firm when hot but not solid.

    I have tightened the clamps, replaced the top hose 3 times in the last year and changed the expansion tank cap at least 4 times. There is no oil in the coolant, no signs of discoloration there. The oil is fine and its not increasing either. I have not noticed any difference to the exhaust, no white/black or steam coming out. There are no bubbles coming out of the bleed screw or the expansion tank when the cap is off.

    Over the last 2 years, I have taken it to 3 mechanics (2 landy ones) and had the head pressure tested. Each time the test comes back clear. This first started happening after the heater matrix let go. The matrix was replaced and system cleaned and cleared. Most of the hoses have been replaced in the last 7 years, the only things not replaced are the thermostat, water pump, cooler O'ring and injector washers.

    My next step is to take it back to the mechanic and ask them to look at it again and possibly pull it apart to find something! Am I correct in thinking it is an undetectable cracked head?

    Has anyone had the same symptoms? What should I ask the mechanics to look for? What are your thoughts?

    Many Thanks.

  2. #2
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    Quote Originally Posted by Scotty85 View Post
    Hey,

    As the title states, my 1999 Defender TD5 is currently having an on again/off again issue with coolant loss when cold. It doesn't always leak and I drove at night and day time, shift worker. When I go to drive for the first time of the day, I check the coolant and find that it may be low so I fill to the cold level (sometimes its not much). I can drive around all day and there is no loss and no signs of loss. I have a temperature sensor and a low coolant alarm fitted which has shown the engine has never gotten too hot or lost any coolant. When the engine cools down several hours later (talking 4 or more), I can find either a small, large or no coolant puddle under the front on the ground. The top hose is firm when hot but not solid.

    I have tightened the clamps, replaced the top hose 3 times in the last year and changed the expansion tank cap at least 4 times. There is no oil in the coolant, no signs of discoloration there. The oil is fine and its not increasing either. I have not noticed any difference to the exhaust, no white/black or steam coming out. There are no bubbles coming out of the bleed screw or the expansion tank when the cap is off.

    Over the last 2 years, I have taken it to 3 mechanics (2 landy ones) and had the head pressure tested. Each time the test comes back clear. This first started happening after the heater matrix let go. The matrix was replaced and system cleaned and cleared. Most of the hoses have been replaced in the last 7 years, the only things not replaced are the thermostat, water pump, cooler O'ring and injector washers.

    My next step is to take it back to the mechanic and ask them to look at it again and possibly pull it apart to find something! Am I correct in thinking it is an undetectable cracked head?

    Has anyone had the same symptoms? What should I ask the mechanics to look for? What are your thoughts?

    Many Thanks.
    Which side of the car does the coolant appear? Seems to me that the fuel cooler is the next place to look.
    ​JayTee

    Nullus Anxietus

    ​Getting involved in discussions is the best way to learn.

    2000 D2 TD5 Auto: Tins
    1994 D1 300TDi Manual: Dave
    1980 SIII Petrol Tray: Doris
    OKApotamus #74
    Nanocom, D2 TD5 only.

  3. #3
    discorevy is offline ChatterBox Silver Subscriber
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    Yes, either fuel cooler "O" rings as Tins mentioned, or if the puddle is more on the other side front, then the "O" ring between the block and the water pump / Air con housing.

    They won't usually leak under pressure, or even when cold with the cap off, seems to be in the transition between cooled down but not enough vacuum to let the cap vent.
    Do the water pump while it's out.

  4. #4
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    Quote Originally Posted by Tins View Post
    Which side of the car does the coolant appear? Seems to me that the fuel cooler is the next place to look.
    It has always been the left side. What I would call the weak points have been the top hose, small hose near the turbo and around the thermostat areas. No loss near the water pump/housing.

    Yesterday I replaced the top hose and the small hose near the turbo. The weak point now seems to be around the thermostat, even though the clamps have been tightened. No signs of coolant loss on the right side of the engine including the fuel cooler.

    I will replace the cooler O'rings as a precaution.

    Can a failed thermostat cause this issue?

  5. #5
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    Quote Originally Posted by discorevy View Post
    Yes, either fuel cooler "O" rings as Tins mentioned, or if the puddle is more on the other side front, then the "O" ring between the block and the water pump / Air con housing.

    They won't usually leak under pressure, or even when cold with the cap off, seems to be in the transition between cooled down but not enough vacuum to let the cap vent.
    Do the water pump while it's out.
    Yes I'll look at replacing the O rings. The leakage is always front left. You are right, it does seem to be around the transition between cooled down but not enough vacuum to let the cap vent.

    Yep I was thinking the water pump and housing, thermostat, O'rings and bottom hose to replace.

  6. #6
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    If you haven't replaced the thermostat but have replaced all the hoses then that would be my first guess. The housing do split.

  7. #7
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    recently gone through this with mine when replacing entire cooling system after head replacement. radiator hoses weeping and breaking hose clamps when tightening to try and stop weeps on thermostat and water pump. Solution was to let the vehicle find its own level in the expansion tank, about 20mm below the cold full line. No more weeps.

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