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Thread: Coolant system blockage

  1. #1
    Join Date
    Jul 2011
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    6

    Default Coolant system blockage

    Hi Guys

    I like to drive my '03 SEAT LEON 1.9 TDI but currently it's sitting on my drive because I have a blockage in the head which is stopping the hot coolant form circulating to the thermostat, so the thermostat isn't opening.
    As you can imagine this is causing massive problems. I have already replaced the thermostat and temperature transmitter with OEM parts so I know the problem doesn't come from there because it's the same as with the old ones.
    I want to tackle this myself and wondered if anyone had ever used a jet wash to flush the head and block?
    I plan to cut the gun from the end of the hose and push the hose end into the head first and then into the block, have you done this before?

    All the best,

    Lee

  2. #2
    Join Date
    May 2007
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    5,240

    Default

    Are you sure it is not a failed water pump?

  3. #3
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    Jul 2011
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    Default

    My first thoughts were water pump, or head gasket but I called out a breakdown technician yesterday to get to the bottom of it in case I had to make warranty claims on OEM parts fitted.
    He did a pressure test and a sniffer and both were good, apparently the fluctuating pressure in the system while it was being revved showed the the water pump is functioning properly. While he did these tests he was monitoring the engine temp on his tablet computer and taking temp readings from the radiator and all of the hoses of the cooling system, he allowed the engine temp to get to 93* and the thermostat hadn't opened. He said that the stat should have opened at about 88* and he was sure that it wasn't going to open now and that the pressure in the system was getting too high to continue with that test.
    His diagnosis is that there is a blockage, most probably in the head that is either stopping or, severely restricting the flow of coolant to the thermostat.

    Lee

  4. #4
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    May 2007
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    Get the thermostat out and check it in a pan of water. It is not uncommon for even a new thermostat to be faulty or to open only at a higher temp than it should.

  5. #5
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    Jul 2011
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    Will do. I'll stick the old one in there too and post back what temps they both open at.

  6. #6
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    Jul 2011
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    I used a digital meat thermometer that hasn't been calibrated to measure the temp.
    The new thermostat visibly started to open at 84* and the old at 91*, by 93* they were both wide open I left them in until 96* but couldn't visibly tell any difference in the 3* so I emptied the pan and ran them under cold water.

  7. #7
    Join Date
    May 2008
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    7,939

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    From cold start the engine and feel the heater pipes where they go into the bulkhead. Obviously both will start off cold then one will get hot quite fast as the water is pumped into the heater matrix. The thermostat will not open yet. If one gets hot quickly and the other is a bit cooler this would show the flow through the matrix is okay. And the heater in the car will blow hot when the fan is switched on. If both pipes remain fairly cool despite the engine warming up then this would indicate the impeller on the pump is not secure. This is a very common problem on all VW group engines. The impeller stays on the shaft but turns a bit slower than it should as it slips under load. Ideally the pump should have been replaced at the last timing belt change.
    However, if this checks out, it could still be a head problem, possibly cracked or head gasket, causing the over pressure in the system.

  8. #8
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    Jul 2011
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    The cambelt, water pump and head gasket were all changed in May this year.
    The cooling system has been pressure tested and a sniffer test has been done, results for both were good. The engine oil in the car is new and has only done about 60 miles, it shows no signs of emulsification.
    The hose temps were monitored with an infra-red thermometer as the engine warmed and behaved as normal until the temp when the thermostat should have opened. Beyond this point they continued to get hotter and the pressure built up with the increasing heat. It reached a point when it became obvious the thermostat was not going to open and the engine was switched off because of the increasing heat and pressure build up.

  9. #9
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    May 2007
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    Quote Originally Posted by Nagaburns View Post
    and a sniffer test has been done
    They often don't pick up problems with Diesels.

  10. #10
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    Jul 2011
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    Developments.
    I got a hose onto the head today and had water passing through and running into the block. I'm not sure how much throughput there should be but it was running out through the thermostat hole quite freely. So I put it all back together and filled the system with coolant and started it up. I put the heater and fans on full and monitored the hoses to and from the heater matrix while the engine reached operating temp. The feed hose increased in temp as the engine warmed but the return hose stayed the same, luke warm, even when the engine reached operating temp and the heater didn't get hot at all. Before I switched the engine off I checked the bottom radiator hose and it was stone cold, the top was hot as expected.
    During all the time the car has had these issues the feed and return from the radiator have never been hard, like they have been pressurised from a cracked head or leaking gasket.

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