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Driving across Europe, i noticed the car was using water. I drove slowly and got to the destination. Since then, the symptoms have been getting stranger.

  • The water loss is caused by excess pressure in the system, no visible leaks.
  • Sometimes the radiator works (gets hot) and the engine does not heat, sometimes the opposite happens. In this case I stop and wait for the engine to cool off so no damage has been done.
  • Today on a stone cold engine we opened the water cap and the cooling circuit was still under a lot of pressure.
  • The water pump is almost brand new.
  • The condition of the thermostat is unknown.

I am not sure what I am looking at here. Any help much appreciated.

EDIT:

After much checking and testing, here is the new status:

I pulled the top hose off and found a small piece of instant gasket from the new water pump last year (I didn't know about this replacement until I took the thermostat out). I think this was blocking the pressure equalizing tube. The thermostat was fine, as was the thermoswitch on the radiator. I drained the circuit : no sludge, and I even ran water both ways through the radiator: it came out clean.

Now when i run it, the top hose seems rather hard, as if there was a lot of pressure in there. Is this normal? Obviously there should be pressure, but before there was less, although this could be that the circuit was filled without being burped. I have refilled it with good coolant, and burped it properly.

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  • Any kind of "smoke" or "steam" coming from the tail pipe? What is the pressure like on the radiator hoses when it is running? Does the heater work properly (i.e. actually blow hot air out of the vents)? – mwhobrey Aug 13 '13 at 15:18
  • No smoke from the tailpipe, and the heater works sometimes. The radiator hoses are not under undue pressure. – Tom Macdonald Aug 13 '13 at 20:57
  • Just curious, but what kind of setup is the radiator (i.e. cap on radiator, external reservoir with fill cap, etc?), and have you checked the cap? Most (if not all) radiator caps have a pressure release system, that could be failing (the pressure rating should be on the cap somewhere depending on the style). – mwhobrey Aug 13 '13 at 21:04
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    Ok we found the problem. There was a piece of instant gasket (from the water pump replacement last year) in the circuit. This was leading to pressure coming back up into the reservoir and pushing water out of the pressure release valve, which is why I was losing water. Also the radiator may have been a bit blocked but we flushed it backwards and that seems to have got rid of the problem. – Tom Macdonald Aug 15 '13 at 12:31
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    @ravloony, you should answer your own question below - that will complete the circuit for people who go searching for similar problems (rather than forcing them to read in the comments) – Bob Cross♦ Aug 21 '13 at 12:42
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The thermostat will open/close when reaching certain temperature. If it does not work properly you can see some of the symptoms you currently have. This is, usually, not an expensive part to replace.

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  • I am taking it out at the moment. We shall see! – Tom Macdonald Aug 13 '13 at 20:58
  • Thermostat was in perfect condition, so I put it back. – Tom Macdonald Aug 15 '13 at 12:32
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There was a piece of instant gasket (from the water pump replacement last year) in the circuit. This was leading to pressure coming back up into the reservoir and pushing water out of the pressure release valve, which is why I was losing water. Also the radiator may have been a bit blocked but we flushed it backwards and that seems to have got rid of the problem.

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