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Discussion Starter #1
I have good engine water temp. When I cycle between hot and cold the air speed changes and am sure I can hear the flap moving. I have replaced the outlet sender, also plugged in a working control head. The heater will work intermittently. Normally on first start, then will just start blowing full cold.


Does anyone else know what else I can do to toubleshoot? I have done everything I have found on the net.


Wow this is a massive bummer - about to go for a road trip in winter..
 

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Ok. So lets calm down and now I need more, betterer advice please. I am not familiar with the W8 cooling system. I was under the bonnet and remember cleaning the connections on the water temp sender once. So to make sure my indications were correct I did that.

Pop - out comes the sender unit, the water shot out. I cleaned the terminals on the plug, replaced the oring, and reinstalled it. Filled it with water.

I drive down the road for 10 min and the engine starts to overheat?!?!? Straight back home thinking there must have been a bubble in the system.

So now its way way worse than before. Whilst the engine is running, the water in the overfill tank will have huge boiling bubbles popping out, pushing the water out. It will settle for a bit, the level will go down, then away it goes again. Far out - I have never seen that before I have no idea. The water sounds like its boiling somewhere. But this is only a very short time after starting the engine. Initially I thought it was just cleaning itself out.

Most certainly not circulating as it should. Feeling the top radiator hose, its only just warm to touch. Is this where I look at the water pump? Hey I could use a bit of advice now - no longer just a heater not working. Its a massive water cooling problem. i just hope I caught it before the engine got too hot. Obviously if the water is not curculating the temp sender didnt reflect the true temp.

Massive bubbles like that - a head gasket doesnt do that does it? Far out - im gutted. I just repainted the car.....
 

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Discussion Starter #4
Hi. Yes I did run a diagnosis. There was a code i will need to go back and see what it was. No I didnt bleed it, the last time I removed the sensor unit it bled itself no problem. I am about to look into that now. The pump and thermostat are original.

I guess that the pump and thermostat are my preferred faults. A blown head gasket is kind of the most worrysome. The bubbles coming up into the fuller tank are more like massive bulges instead of the normal trickle stream you would see from exhaust.

So I am about to start troubleshooting the cooling systyem.
 

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Do you have VCDS? Scan for codes related to the cooling system and other temperature related issues that will effect ECU monitoring.

The order in which the overheating problem on a W8 is as follows. This is according to recorded customer complaints from various sources.

1) Failure of the electric fan.
2) Failed water pump.
3) Failed thermostat.

You might have a thermostat that's stuck closed and or a water pump that has failed or is failing.
Both of these issues will cause severe boiling of the water.
 

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The chances of a blown head gasket is more unlikely than having a failed t-stat or water pump.

Find out what that code was and post it up.
How many miles on the car?
 

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Just an FYI, we now have a dedicated Forum for W8's.
 

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Discussion Starter #10
Good morning. I thought I would update on this. Yesterday I pulled out the thermostat. Reason being it has been throwing the engine light for a number of years now (the heater open circuit) so even if it wasnt that - it needed replacing anyway.

So - after breaking several electrical plugs off the fuel injectors and the little brittle lug on the top radiator hose. (darn it I was SOOOO careful). Actually I must sound like an animal.

I pulled the thermostat. Placed it in boiling water - and its quite well and proper closed up thanks very much. Now the W8, that thermostat should open just like all the others aye???

Diagnosis - I think, that the thermostat was on its way out. The heater not working, was a good sign of poor flow. Its winter here in NZ. Perhaps, possibly, the gush of water that came out, the sudden loss of pressure, may have just tipped the thermostat from being kind of serviceable - to closed and naughty.

They are tear-forming expensive here in NZ. I have bought one from the USA and will report back once installed.
 

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Yes, when you put the thermostat in water and bring up to temperature, it should open just like any other automobile thermostat.

To bad you couldn't have waited a few more days.
I'm doing an experiment with my failed thermostat using a thermostat from a W12. The W12 thermostat is almost 50% less than the one specified for the W8!
 

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Discussion Starter #13
With much joy and jubilation I received my thermostat. And it didn't rip a hole in my wallet. Although once again, why do we have to purchase the whole housing as well?

Well the good news is I dont have an engine light thrown up by the little unnecessary heater in the housing.


But I am still getting a boil in the engine jacket. Strange, and the heater still wont go. I reckon its the water pump or there is a blockage somewhere. But if I put the cap on, the vehicle holds temp at bang on 50deg normal if I run it for a period. So any ideas about this? Do I start pulling the cooling system apart? I did start to pull the water pump out - until I found I couldn't due to lack of tooling.,

Please if someone could shine a light on the bolts that hold the water pump in????? Is it a 5.5mm 12 point torx kind of socket that gets them out? I have a 6mm and a 5mm, I guess I could hammer in the 6mm but thats not very professional huh haha - but please if someone knows this, is it a special VW tool?.
 

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Etka identifies the bolt as N 105 314 01, screw, csk. with polygon socket hd. M8 x 25.
I suspect "polygon socket hd" means Tri-Square, like the bolts that hold the door latches on. The tri-square set I have has three sizes.
 

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On this era passat there is a small hole drilled into the heater core hose barb that sticks out of the fire wall. You have to pull the hose back past this hole with engine running to remove the air. I'd try that first and for most. I am concerned about the bubbles your seeing in the cooling system. They could just be air still perking but I'm doubting it. To me that is a tell tale sign of a head gasket. It could be compression gasses getting pushed into the cooling system. Where do these gasses go? Up to the highest point. In our case the heater core. That means no heat. I'm doubting its a water pump but it could be. The water pump bolts are triplesquare.
 

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Discussion Starter #16
I found the bolts to remove the waterpump were able to be removed by a 6mm 12 point spline-drive socket that needed to be tapped in by a small knocking device.

After much gnashing of teeth, and one easyout application I have removed the water pump. And I tell you what, I have NEVER, had to pry and pull as much as I did to get it out of the engine block. I actually ended up snapping one of the mounting lugs off in the process. So a new waterpump was needed anyway. Final removal was making a bracket to screw on the pulley mount, welded onto a bar, so I was able to gently rock the pump out. Wow - I felt like an animal. Although the bar did make the process gentle.

Anyways - there is nothing wrong with the pump. Its sweet as except for the lug dammit. A $200 replacement has arrived.

Mr (or Mrs) Bigfun. Hey I keep thinking its a head gasket? I guess the only way to check is to pressurize the water system huh? Or do a cylinder compression test? Watching the overfill tank, the bubbles seem to be very large burping bubbles, and quite large expansion of the water. To be honest, once it starts getting hot to the point where I see the water starting to evaporate I actually stop the engine. But - and the big but, is when I put the cap on, and run the engine, it stabilises, and sits true at 50deg (or at 12:00) exactly where it should. No hotter no colder. I have been driving this vehicle without an operational heater for 18 months. Surely a blown head gasket is not going to let me do that? Very strange. Its like I am back at square one, the thermostat has resolved one issue the heater still wont work.

I am going to install the new waterpump today. And I am going to bleed the air out from the barb like you have mentioned, and see what happens. And will actually see if the pipes to the exchanger get any warmth. I checked it for flow yesterday and its definately clear - almost too clear, I was able to blow down one tube to get water out the other end. I was wondering if it should be that easy to blow through all the galleries in the heat exchanger.....

I love my VW. I am unsure if I love it enough to replace a head gasket. A heater wont be needed this summer in NZ - but - being an engineer I cant have faults. I am going to perform this maintenance today, and cry into my wifes chest tonight if I dont succeed.
 

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Discussion Starter #17
Update! Installation of a new waterpump is the opposite of the removal except I didnt need the bar nor did I need the eazyout. A piece of cake although I replaced the mounting bolts with some antiseize so the next punter who takes it off wont go through what I did.

The vehicle now runs with a new thermostat, and a new water pump. Strange - this time on start the overflow tank didnt bubble nearly as much as before. I took a good look at the pump that came out, and it was fine to me. The W8 engine takes a long time to reach normal operating temperature, but it sat there happily ideling, reached 50deg, used a bit of water as the air came out. I even took it for a drive, up a couple of hills, rock stable engine temp.

Still no heater. Not a sausage. Reaching into the well underneath the screen, I was able to feel the pipes leading into the heat exchanger. Only one, the one with the little fork on it (according to the manual the inlet) was slightly warm.

I am completely stumped. The comment about the head gasket pushing air into the system and it going high stopping the heat exchanger from working is a good one, yet I would have thought I would be having severe overheating issues? I also see two check valves in the system - I wonder where they are I couldnt find them.

Hey so if anyone out there has an idea on where to further troubleshoot this I would be keen to read about it. Such a simple concept yet it wont work. At least I am no longer chasing an overtemp issue.
 

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Unbolt coolant reservoir and lift it as high as you can. You might have to unplug the coolant sensor on tank.

Fill the tank full.

Unclamp the heater hose that connects to heater core that has the hole drilled in it and has an arrow on it.

Slide hose back off heater core end so the hole can vent. Keep filling res/tank until pure coolant and no air is coming out of hole in the hose.

Slide hose back on and reclamp.

Reassemble tank.

.......test run. ????

I'm 99% sure you have air trapped in heater core. Weather it's from compression gases from head gasket failure or just improper bleeding is hard to tell. I don't believe the w8 has coolant valves to shut off flow. I will look at mine perhaps tomorrow. I also have a complete extra motor in the garage I can peek at. I've had 5 w8 cars so I'm not new to them. I've just never had cooling issues.
 

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Should be left heater hose if looking from front if I recall. The heater is the highest point so if air is up there it will not come out without bleeding. Just keep filling tank with it elevated until no more air is coming out just coolant. I've done this on 1.8s and v6 cars but not a w8 but should be same. Sometimes it takes a bit. You can do it running but this is probably simpler.
 
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