1998 A4, 2.6 V6 Still Overheating, after changing Thermostat, Water Pump, timing belt

[stokie]

Hi everybody,
Any help solving this mystery would be greatly appreciated.

My A4 was recently purchased in an unknown state. The engine was overheating in a couple of minutes, with no bubbles in the header tank, just rising water level. (Cap was off)
I suspected a broken impeller on the pump.

I read in several of the Audi forums that the way to diagnose a faulty pump is to run the engine and look for water coming out the small return hose to the top of the header tank.
There was nothing there, no movement at all in the water in the tank, so I went ahead and changed the pump, thermostat and timing belt.

Turns out that the pump was fine, the thermostat opened in boiling water as expected, and the belt looked about 1/4 worn.

I ran water from a hose through the radiator in case it was blocked. Flowed easily.
I ran water through any hose connection I could easily get to and it seemed that the flow was ok wherever.

I reassembled everything, filled the motor with water, doing as much top and bottom hose squeezing as possible to burp it, then started the engine. It ran nicely, but again NO movement in the water or flow from the small return hose.

I took it for a gentle test drive. About 4 min later, the temp gauge was hardly moving above 60 degrees, when the temp warning light started flashing on the dash.
I limped home (about 1 min) and the water was boiling when I got there.
Radiator was hot top and bottom.

It seems like the pump isn't allowed to circulate the water for some reason.

Quite frustrating.http://www.audizine.com/forum/images...es/bawling.gif

Does anyone have a water circulation diagram for an Audi V6?

This may be related: The previous owner had a sudden massive cabin leak in the heater core or similar, so joined the 2 heater hoses together above the back of the motor.

Thanks.

[RagtagXMASTER]

Any chance of a cloged or restricted heater core?


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[stokie]

Any chance of a cloged or restricted heater core?


Sent from my iPhone using Tapatalk

The previous owner had a sudden massive cabin leak in the heater core or similar, so joined the 2 heater hoses together above the back of the motor.
Are there any other heater hoses than these?
From memory I undid the makeshift joiner and ran hose water into both ends - water flowed and one way came out the header tank I think.
I'll check again.

[elduderino200]

Can you re-connect the input/output hoses that go to the heater core and drive around just to eliminate that from the equation during diagnosis?
It shouldn't get cold enough for a few months that you'll need it, I would think.

Any white smoke from the exhaust?

[stokie]

I disconnected the 2 joined heater hoses and when the engine was started (cold) there was no flow from either of them. Running the hose into each of them produced water coming out of either the opposite heater hose, or the header tank.
So it looks like there's no blockage there. Would an air lock there be possible?

[stokie]

The exhaust seemed fine, nothing unusual. We're heading into winter here in New Zealand, so a heater would be nice.
I just ran the engine with the heater hoses disconnected from each other and there is no water coming out of either one - I didn't warm the engine up to 90 degrees though. They join exactly at the level of the heater connection points, so I can't see what difference it would make - also wouldn't want to flood the cabin with water.

[elduderino200]

Oh right I forget not everyone lives in the northern hemisphere... sorry!

Anyway, I think water wont flow through either of the pipes until the engine heats up and/or you turn the heat in the cabin on high.
In any event, if you get a 90 degree elbow piece that fits the two hoses that go into the heater core, you can 'section' it off. I would suggest that for a few days during the diagnosis process... just to be SURE it's not an air bubble in the heater core.

If you have access to a pressure gauge, you may want to test compression - just to rule out a head gasket issue, and piece of mind it's not a major issue.

[stokie]

OK, progress so far: Today I spent time squeezing hoses and getting as much air out as I could, while topping up the water.

I started the engine and as usual there was still no flow from the small return hose.

I put the cap on and warmed up the engine at 1500 rpm. The water temp gauge (I had been mistakenly looking at the oil temp gauge last night in the dark with my headlight torch) steadily moved up past 90 to 100 degrees, when I turned the engine off.
The radiator was hot at the top and cold at the bottom. The heater hoses both felt hot, pressurised, and full of water.

The electric fan failed to start.

The exhaust looks normal, there is no fuming from the oil filler, there are no steam bubbles in the header tank.
Has anyone ever heard of a blockage in a hose or the cylinder heads?

[stokie]

Oh right I forget not everyone lives in the northern hemisphere... sorry!

Anyway, I think water wont flow through either of the pipes until the engine heats up and/or you turn the heat in the cabin on high.
In any event, if you get a 90 degree elbow piece that fits the two hoses that go into the heater core, you can 'section' it off. I would suggest that for a few days during the diagnosis process... just to be SURE it's not an air bubble in the heater core.

If you have access to a pressure gauge, you may want to test compression - just to rule out a head gasket issue, and piece of mind it's not a major issue.

That's a good suggestion with a compression test - I think there's a tester at my part time work place.

[Bordom]

I was going to say rad, but it now sounds like a blockage within the block/heads itself. Most strange

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