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Coolant temperature too high - even tore engine apart

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  • Coolant temperature too high - even tore engine apart

    Hi everybody,

    I am close to finishing my EFR turbo build on my S2 3B. I did a few test drives tuning the car, but my coolant temperature always got too high. Cruising at 2000rpm caused a CLT temp of 102°C (measured in the cylinder head, G62 sensor).

    S2 3B, EFR turbo, custom intake and exhaust manifold, EMU Black ECU, stock cooling setup with AC condenser.

    Troubleshooting so far:
    - EGT is fine- 350-400°C in idle, max. 650°C when cruising
    - replaced coolant, water pump, thermostat, G62 CLT sensor
    - made sure cooling fan spins up
    - bled the cooling system at the main cooler and the hose for the heater core
    - made sure all coolers are getting hot
    - made sure the timing is on point
    - made sure calibration in the ECU is correct
    - did a co2 test on the cooling system --> liquid turned form blue to green

    - possible faulty head gasket or crack
    - --> tore the engine apart
    - didn't see any exhaust gas paths on the flat surfaces or on the gasket
    - didn't see any lighter spots in the engine, which water would cause
    - checked block and head with a straight edge and feeler gauge -> both very flat, my 0,05mm feeler gauge didn't fit at all
    - didn't see any cracks in head, exhaust port or block

    I'm not even sure the positive co2 test is the cause of the hight CLT temps. But don't want to assemble the engine and still have the same problems. Do you have any tipps on what to do next?

    Attached Files

  • #2
    Get the head pressure tested and perhaps even Xrayed as the CO2 in the coolant must be coming from the combustion chamber so shouldn't be there regardless. Some cracks are very hard to see with just the eye.

    Though you could just have been unlucky with the head gasket. That head does look to be in very good shape, it maybe a myth but I've found 3B heads less crack prone than ABY/AAN/ADU ones, they do still crack but it's rare.
    1989 B3 2.0 3A 80 quattro... Budget 1.8T Project.
    1992 C4 100 2.8 Avant quattro... Mobile Sitting Room.
    1995 RS2... MTM K26/7 380 BHP Conversion.
    1990 Corrado G60... Breaking For Parts.


    • #3
      Was it a metal head gasket or the original composite??

      S2 Coupe 3B Project

      Ur quattro restoration

      S2 Avant

      Boost is the new rock and roll!


      • #4
        Yes, the metal head gasket was already installed. One of the previous owner renewed the engine. Looks to be done very nicely. I will just put it together with a fresh head gasket and ARP head studs. If the co2 test will still be positive, I really have to get the head checked. But seems like it's worth a shot.


        • #5
          A question , the water does not look fresh at all. You wrote that you have replaced the coolant. My coolant look as brand new. Did you flush the radiator ? Put a hose in the upper hole and just flush until its clean .. it can have dirt in it then it will not cool. You can flush with hose threw engine to. I would have tested the head for cracks since you already have removed it. If it still gets hot you will have to meove everything change the gasket and so on. Time and money. Checking the head is not so expensive.