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Thread: Overheating

  1. #1
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    Overheating

    My second hand 2010 Passat 1.6 TDI and 144,000 miles has an overheating problem, new water pumps (main pump and electric), a new thermostat and new oil cooler plus sensor have all been fitted. No luck and still overheats. No error codes at all.

    All hoses and pipework have been removed and shown to be clear. The car works fine until a long incline in say 5th gear and the water temp and oil temp then climb to 140 degC water and sometimes 130degC oil. The heater produces blistering heat at all times, temperatures go back to 90 water and about 110 degC oil by continuing in 3rd gear with revs at about 3000. This reduces temperature to normal in about 2 minutes.

    Very oddly the radiator never gets hot at all and remain luke warm, the electric fans work. Main dealer has done leak test looking for combustion gas in coolant and found no trace of blown head gasket. There is no water in the oil. A second new thermostat has been fitted just in case. The system has been flushed and the radiator tested and no blockages found.

    VW main dealer has run out of ideas and after 2100 reckons only option is a new engine. The biggest mystery to me is why the radiator never heats up. As a test I ran the car for a few days without the thermostat and the engine temp never got higher than 60degC but for the first time the radiator did warm up.

    Any thoughts on what is going on and how to fix much appreciated. VW and Halfords motor centre have both plugged in to look for error codes and nothing showing. When under load could the EGR be putting too much hot gas back into the inlet manifold causing an overheat and when revving at 3000 the exhaust temperature lowers and things revert to normal? A mystery I would very much like to solve!

  2. #2
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    Even if your theory about EGR is correct then the thermostat should still be able to regulate the temperature by opening up. Sounds weird as I would have expected error codes.
    2005 Golf 1.6 FSI, BLP

  3. #3
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    Quote Originally Posted by lemta View Post
    Even if your theory about EGR is correct then the thermostat should still be able to regulate the temperature by opening up. Sounds weird as I would have expected error codes.
    Thanks for your interest, I gave the cooling system another very thorough cleaning with Forte Bio degreaser on the basis that perhaps sludge had built up in the engine block/cylinder head and for a half hour drive all was well, no overheat despite pushing engine hard, it seemed like a breakthrough but now back to old problem. Pipework round the back of engine to EGR cooler is cold as is main radiator. Sometimes there is pressure in main hoses to and from radiator at other times hoses are soft and always tepid. I have made sure system is free of air. When overheated and reservoir opened a lot of bubbling and back flow driven I suppose by steam. Am tempted to re dose with Forte cleaner and leave in the system for a few days but perhaps a bad idea in case it damages seals etc.

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    Administrator Keithuk's Avatar
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    Welcome to the forum.

    Its nice to see you made an intro on your own.

    No error codes scanned with what?
    2010 Golf GTD (170) CBBB, 5 Door, Shadow Blue (P6/D5Q), Transmission Code: KXZ, Flat Tyre Indicator, Basic Protection Pack + VCDS.


  6. #5
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    Quote Originally Posted by Keithuk View Post
    Welcome to the forum.

    Its nice to see you made an intro on your own.

    No error codes scanned with what?
    VW have scanned it so it's safe to say that there are no error codes logged.
    2005 Golf 1.6 FSI, BLP

  7. #6
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    There were no error codes indicating a fault eg associated with the EGR which I thought might be feeding too much hot gas back to inlet causing problem. This morning in order to be 100% sure there was no air in the system I removed a small 10mm pipe which runs to the elbow on the top hose where it joins radiator and at the other end to a tee piece heading off to the reservoir and found it blocked. There appears to be a restrictor in the pipe perhaps a check valve? which seemed to prevent flow in any direction, some compressed air and it cleared with the car now warming up as normal and staying at 90 under all driving conditions. Too early to be confident as have had a few days of apparent trouble free motoring with overheat only to return. Any ideas on purpose of the restrictor much appreciated, feels like a hard section about 10mm long approx 100mm from radiator top elbow.
    2010 Passat Estate 1.6 TDI-CR

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  9. #7
    Administrator Crasher's Avatar
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    Classic CAYC engine head gasket lifting under load, it is not possible to test for this so you just have to trust your instincts and judgement.
    2003 Skoda Octavia VRS Estate. APR 98RON remap, APR R1 diverter valve, Jetex exhaust, K&N panel filter, 7.5x18 Alutec Monstr wheels with 225/40 18 Uniroyal Rainsport 3 tyres.
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  10. #8
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    It does seem to match what I'm seeing but if head lifts and puts gas into the coolant surely the VW garage when they did a gas analysis of gas coming from the coolant will have detected tell tale signs eg CO2 or hydrocarbons etc?
    2010 Passat Estate 1.6 TDI-CR

  11. #9
    Administrator Keithuk's Avatar
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    Its been many years since I done a gas analysis on a petrol engine for pressurised cooling system, a diesel is slightly different. We also had a chemical analysis that tests the air in the cooling system it changes from blue to yellow if there is CO2 there.

    Get the cooling system pressure tested?
    2010 Golf GTD (170) CBBB, 5 Door, Shadow Blue (P6/D5Q), Transmission Code: KXZ, Flat Tyre Indicator, Basic Protection Pack + VCDS.


  12. #10
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    Quote Originally Posted by Keithuk View Post
    Its been many years since I done a gas analysis on a petrol engine for pressurised cooling system, a diesel is slightly different. We also had a chemical analysis that tests the air in the cooling system it changes from blue to yellow if there is CO2 there.

    Get the cooling system pressure tested?
    There is no water in the engine oil or oil in the coolant and VW are confident that the head gasket is fine having tested and found no gas in the cooling system. I am tempted to try one of those advertised head gasket sealants that supposedly cure a blown gasket, a last resort but would be very interesting if the problem then disappeared. Completely baffling that despite a hot engine to hose to the thermostat is tepid so clearly the stat is not opening. Another thought I had is to remove the stat and drill a small weep hole say 4 mm through the thing to allow water or air through so that the stat sees the hot water and opens. Am guessing an airlock builds up around the stat preventing it from detecting the actual coolant temperature. Not really a long term solution as need to deal with air/gas build up if thats what it is.
    2010 Passat Estate 1.6 TDI-CR

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