Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose

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Mon 12 Nov 2018 21:42
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - F1Lane

Hi All,

So I've been having some trouble with my 2005 1.9TDI Golf for around 6 months now. The heater in the cabin does not work, only on very rare occasions. To try and resolve this it's had a new temperature sensor and new thermostat. The issue has continued, so the thermostat was replaced again to ensure it was not faulty.

However the bottom hose on the radiator remains cold, the cabin gets hot (until what seems like the thermostat opens) and the fans cut in. But still the bottom hose and radiator are stone cold, whilst the top pipe is boiling and the reservoir steaming when opened.

We have run the car to try and remove all of the air from the system and get it nice and hot so the thermostat is open and water flowing. But after the stat opened and the fans cut in, the cabin went cold and still, the bottom pipe is freezing and the top pipe burning.

There is good flow in the reservoir, so it seems very unlikely it's the water pump, which was a commonly suggested fix. But if water is flowing it seems odd for the pump to be the cause. The reason this is such an issue is I arrived home one evening and the car smelt like burning. It turns out this was the water boiling in the reservoir!

Sorry for the long message and poor writing, but if anyone has any suggestions, I would massively appreciate it!

Thanks,

F1Lane

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Mon 12 Nov 2018 22:31
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - galileo

Sounds as if the radiator is blocked, have you tried disconnecting both hoses and flushing it with a hose?

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Mon 12 Nov 2018 22:58
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - elekie&a/c doctor
I'm inclined to think this may be a water pump issue. What often happens on these ,is the impeller becomes loose on the water pump shaft ,so it free wheels with consequent lack of coolant flow. You will need to strip it out to confirm. You will need to do the cam belt at the same time.
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Tue 13 Nov 2018 09:58
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - Railroad.

Running the engine will do nothing to bleed air out of the system. The thermostat on these engines is located in the return from the radiator to the block rather than in the flow from the cylinder head to the radiator. Like most diesels it's also a two stage thermostat which incorporates a bypass to allow coolant to circulate around the engine when the thermostat is closed rather than the coolant having nowhere to go. This prevents hotspots forming in the cylinder head. When the thermostat is closed the system is effectively divided into two parts. If the system has been disturbed, and yours has, it's possible for air to get trapped in the block. You need to remove the highest component in the system which is on the engine side of the thermostat to allow air to escape. Because coolant is heavier than air the air will be forced out through the opening. Do not start the engine to try and remove the air because it won't. As I said the thermostat is in the return and so it won't open until the block gets hot.

Try bleeding the system correctly first. If that doesn't solve your problem then I'd be inclined to agree with the Doc in saying it's most likely the water pump impeller loose on the shaft.

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Tue 13 Nov 2018 17:55
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - F1Lane

Thank you for the response, I will get this looked into.

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Wed 14 Nov 2018 17:19
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - F1Lane

Spent a long time bleeding the system today, seem ok I think!

It's hard to know, but what happens now is, the heater gets hot pretty quickly, sits at 90C engine temp. Then after a fair amount of driving (20 - 30 mins) the heater cools down, then heats back up after maybe 2-3 minutes. I assume this is normal? As I guess the thermostat opens, the radiator and fans then cool the system, then it closes again and warms up even more and then repeats?

Car runs fine, but very paranoid after all these issues!

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Fri 16 Nov 2018 14:46
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - dieselnut

No that's not how it works.

From cold the coolant circulates from the engine just to the heater.

It stays like that until the temperature reaches 90C & you have good heat from the heater.

At 90C the thermostat starts to open a parallel circulation route to the radiator.

The stat only opens a little & bleeds off just enough heat to keep the coolant temp at 90C.

So now you have 2 parallel coolant paths, one to the heater & another to the rad.

If the thermostat is working properly the coolant will stay at 90C.

These 1.9 PD engines are very efficient & you are unlikely to get the bottom hose hot unless you've been thrashing it up the motorway for a few miles.

It sounds like you may have a head gasket leaking, pushing air into the coolant giving an air lock in the heater.

Have a look in the coolant bottle from cold, see if you can see small bubbles coming to the surface, or get a combustion gas check kit & check the coolant that way.

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Mon 19 Nov 2018 18:44
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - F1Lane

Oddly it was fine on the way to work, way home no heater again.

But if i pick it up to 3 - 4k RPM i get nice warm air. I assume this is a sign the water pump is on the way out and the flow of coolant is poor. The only thing that worries me is i can hear air coming out of the water tank, but if it's been boiling up I guess that could break the lid on the water bottle.

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Mon 19 Nov 2018 18:46
Volkswagen Golf TDI - HELP!Cabin temperature & Bottom Radiator Hose - F1Lane

So stupid question. I assume the waterpump is attached at a point where it doesn't matter if the thermostat is open or not, it will make both sections of the system flow (if the stat is closed, the flow is still fine because the pump is spinning)

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