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Old 03-16-2013, 05:31 PM
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Default Can someone please solve my overheating engine problem?

I am totally puzzled with the overheating condition on my 2.0 AZG engine. Everything was going fine until I had a check engine light (P1296 code) trigger. So I replaced both the thermostat and coolant temperature control sensor with OEM from the dealer, and pressure tested the cooling system. I thoroughly purged all air with a cooling system charge tool (twice). Also, I checked the water pump impellers from the thermostat housing side twice and turned the crank pulley for operation - from the inside "feel test", there is no play or loose impeller - and from the crank turn, the impellers turn correctly. Finally, there are no external leaks anywhere or loss of coolant.
Shortly after the repair, the dreaded red flashing/beeping light triggered, indicating a low coolant or overheating condition. So I actually replaced the CTS and thermostat again, to rule out any defect product. To no avail, the car is still overheating - as I drove around with a scan tool measuring coolant temperature. At first, it seems fine cycling between 190-200, and then falling back. But after driving 20+ minutes, the temperature climbs to 225-240, at which point red light flashes and so I shut the engine down. Ironically, the cabin heater blows warm/hot air until that point where the engine begins to run hot (overheat) - at which time the heater starts to blow cool air! Here are some additional observations:
1) The auxiliary cooling fans work perfectly and run full time after engine runs hot
2) Both top and bottom radiator hoses are hot after engine is fully warmed up (or overheating)
3) I don't have the dreaded white plume exhaust - signs of a blown head gasket.
4) There is no coolant flow into the expansion tank from the upper return hose, even under high RPM. I also tried to blow compressed air through the hose with no luck - it appears totally and solidly blocked, perhaps at the throttle body side or elsewhere, as I have not yet traced the source or cleared the blockage. But before I clear the blockage, my biggest question is: would a blocked expansion tank return hose cause an overheating issue or would coolant still circulate the system with the expansion tank return hose blocked??
I am at a complete loss......someone please help.
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Old 03-16-2013, 06:10 PM
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Car: 1999 GL 2.0
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The problem could be a partially plugged radiator. It allows some coolant flow but not enough to keep the engine cool for long. The blockage of the small tube running to the expansion tank may be related to whatever caused the radiator blockage as well.

Check the radiator fins as well. I've seen other cars where the fins will completely crumble and greatly reduce the effectiveness of the radiator.

If you drain the radiator, try disconnecting the lower hose and then the upper hose at the coolant flange. Pour water into the upper radiator hose and see how fast it goes through the radiator. You shouldn't be able to pour it in fast enough to make the hose overflow.
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Old 03-16-2013, 08:11 PM
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Default Re: Can someone please solve my overheating engine problem?

Have you mixed coolants at all?

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Old 03-16-2013, 08:25 PM
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Quote:
Originally Posted by red99 View Post
The problem could be a partially plugged radiator. It allows some coolant flow but not enough to keep the engine cool for long. The blockage of the small tube running to the expansion tank may be related to whatever caused the radiator blockage as well.

Check the radiator fins as well. I've seen other cars where the fins will completely crumble and greatly reduce the effectiveness of the radiator.

If you drain the radiator, try disconnecting the lower hose and then the upper hose at the coolant flange. Pour water into the upper radiator hose and see how fast it goes through the radiator. You shouldn't be able to pour it in fast enough to make the hose overflow.
Thank you. I will try your suggestion to check for blockage in the radiator - and do you think that assuming the radiator is unobstructed, that the blocked expansion tank hose could by itself cause the overheating? Thanks again.
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Old 03-16-2013, 08:37 PM
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Quote:
Originally Posted by Smileybug View Post
Have you mixed coolants at all?

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I was running Pentofrost SF (G12equivalent), but topped off with real G12 after the thermostat replacement. Of course, I diluted it with water 50/50.
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Old 03-16-2013, 08:48 PM
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Quote:
Originally Posted by hedzup View Post
do you think that assuming the radiator is unobstructed, that the blocked expansion tank hose could by itself cause the overheating?
I don't think so, unless some air could be getting in through the headgasket. It would cause problems getting the air out while filling the system and may allow air entering the system to cause a blockage. I would definitely fix it.
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Old 03-16-2013, 08:50 PM
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Quote:
Originally Posted by hedzup View Post
Everything was going fine until I had a check engine light (P1296 code) trigger.
Are you sure about "P1296?" I don't find any info about VW using that code.
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Old 03-16-2013, 09:49 PM
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Quote:
Originally Posted by red99 View Post
Are you sure about "P1296?" I don't find any info about VW using that code.
Wiki-Ross has P1296 bundled in with two other codes:
17704/P1296/004758 - Ross-Tech Wiki
And I did check the radiator fins for damaged or obstruction too. I appreciate the theory that the obstruction could be somewhere else in the system, and not necessarily at the expansion return hose - which would make sense that flow going into the expansion hose would get restricted too. I will have to check flow from the top to the bottom of the radiator (easy to do) before I start disconnecting hose after hose from the expansion hose onward.
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Old 03-20-2013, 04:42 AM
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Quote:
Originally Posted by hedzup View Post
Wiki-Ross has P1296 bundled in with two other codes:
17704/P1296/004758 - Ross-Tech Wiki
And I did check the radiator fins for damaged or obstruction too. I appreciate the theory that the obstruction could be somewhere else in the system, and not necessarily at the expansion return hose - which would make sense that flow going into the expansion hose would get restricted too. I will have to check flow from the top to the bottom of the radiator (easy to do) before I start disconnecting hose after hose from the expansion hose onward.
Update: Overheating problem solved! Blocked upper expansion tank hose was the culprit - preventing proper coolant circulation and more importantly, purging of air from the cooling system. I traced the blockage from the hose end to the throttle body cooling channels. Once the throttle body was removed, I sprayed carb cleaner several times through the inlet and outlet nipple to dissolve scale buildup. Then, I pumped compressed air through the nipples to purge the loosened scale, and let it dry before reinstalling. After reconnecting the hoses, flush and fill, and no more dreaded red/beeping red light. And of course, coolant now flows like a faucet into the expansion tamk at idle.
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Old 03-20-2013, 12:17 PM
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Good to hear the problem is solved! That is one more thing to check when people report overheating. I guess that the air in the system builds up at the coolant flange and coolant can't get through. It may not take too much do it.
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Old 03-20-2013, 06:01 PM
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So what blocked the hose up? sludge? just so other folks with similar problem know what to look for in the future. Glad u found your problem though.......
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Old 04-06-2013, 01:05 AM
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Default Same but different

Hello all. I have the exact same problem as the OP except my blockage goes all the way back to my engine block. My TB and hoses are all clear. Also, I do believe the previous owners decided to put any coolant in the system as when I drained and flushed it, it was bright green. What should be my next step?

Thanks
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Old 05-03-2013, 07:39 PM
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What did you spray with carb cleaner? Was it the throttle body that was clogged? I have the same issue. Cleaned all hoses from expansion tank but still no circulation.
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Old 05-03-2013, 08:22 PM
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I didn't use carb cleaner. My throttle body was clear. My blockage is in my engine block itself. Right now I am having the water pump, belt and pulley replace so I will see how it goes from there. Im hoping I can run a coolant flush through it and clear the blockage.
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Old 05-04-2013, 10:01 PM
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I have cleaned all the hoses and it seems the block is clogged also. Any ideas on how to flush the engine block? I have already changed the timing belt, waterpump and thermostat. Didnt see any blockage when I removed the old waterpump. Stuck right now??
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Old 05-04-2013, 10:26 PM
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Have you tried poking a piece of wire into the barb fitting to open up the passage into the cylinder head? So, if you disconnect the hose from the cylinder head and pour water in, it comes out at the reservoir?
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Old 05-05-2013, 12:46 AM
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I did the wire thing but you can only push it in so far then the coolant passage makes a sharp 90 degree. No water in or out that passage. I can't even blow air through the passage. I'm lost too.
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Old 05-06-2013, 02:29 AM
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Ok guys I poked a paperclip into the barb on the block (drivers side) and cleared out some debris. I now have flow into the reserve tank. Not sure if the flow should be pressurized or just slow flow. I did notice with throttle, flow increases somewhat. Fans still wont come on without using the a/c switch but im sure the thermo sensor on the radiator will fix that. THANKS AGAIN.
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Old 05-06-2013, 02:44 AM
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congratulations on the successful fix!! I still have a clog I can't get to so I will try a flush asap to see if that helps. Like I said earlier, when I blow on the hose that connects to that barb I can't even get air to go in there. Wish me luck.
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Old 05-06-2013, 07:35 PM
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Default Overheating - just 2 cents worth

My wifes 05 NBC Turbo.
Overheating a couple of years ago.
Replaced the water pump - still an issue.
Discovered the Secondary water pump - pesky plastic impellers had broken up and clogged the system.
So just remember to check BOTH water pumps.
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