97 Cab 2.6 - No engine temp registering

[Andrew Bell]

Took the car on a longish journey recently, about 15 minutes in I noticed the engine temp wasn't going above 60.  It was early hours and freezing cold, so assumed that it was ambient temperature plus not driving far or fast at that point.  Turned the heaters on and got no warm air and another 30 minutes later still no rise in engine temp.

Thought it might be an air lock in the cooling system, so pulled over at a services, checked coolant & oil levels (both Ok).  Bled the coolant lines (from the plastic screw near the windscreen), fluid came out almost straight away.  

Rest of the journey there and back no change in engine temp and no heat from the blowers.  

Got home, swapped the coolant temp sensor as that seemed the next likely culprit.  Noticed that the coolant level had dropped from Max to Min, so topped up and bled again, some air came out, but again, not a lot.  Started the car and left it to idle on the drive, with an occasional blip of the throttle.  After a few minutes the temp started rising, got to about 80-90, so I assumed all was good.

Car sat for a couple weeks, took it out last night and once again, no warm air and temp gauge sat at 50-60.  Checked the rad and hoses, both are getting warm then hot as the engine runs, so assuming that coolant is actually circulating.  Oil level hasn't dropped and engine is hot after being driven, so think that side of things is ok.

Noticed that there does seem to be a little coolant leaking from the bottom radiator hose.  Not sure if it's original, but it's definitely far from new - neither hoses or radiator have been changed in the 11 years I've had the car and up till now there's never been an issue.

I'm wondering if the hose has perished and is letting air in, causing a semi permanent air leak / lock.  So replacing them is the next job, except, I can't seem to find anywhere online to buy replacements - Can anyone point me in the direction of a supplier.  I have the OE part numbers, but searching online either yields "Discontinued" from Audi, or hoses from other sources (such as AutoDoc) that match the part number, but look nothing like what's under the bonnet.

Lastly, if it turns out not to be hoses, what should I look for next?  I'm assuming the water pump is working as I can feel coolant moving through the hoses and it comes out the bleed screw.  I'm reasonably sure the block is ok as it had a strip and rebuild over lockdown and hasn't done more than 1000 miles since, so would welcome any advice or suggestions.

TIA 

 

[Magnet]

Hello Andrew,

I’d go straight for a new thermostat. It probably goes without saying that if the coolant isn’t reaching its ‘normal’ 90 degrees operating temperature, then you aren’t running hot coolant through the heater matrix, so cannot expect hot air from the vents. 
Kind regards, 

Gareth. 

[Andrew Bell]

1 hour ago, Magnet said:

Hello Andrew,

I’d go straight for a new thermostat. It probably goes without saying that if the coolant isn’t reaching its ‘normal’ 90 degrees operating temperature, then you aren’t running hot coolant through the heater matrix, so cannot expect hot air from the vents. 
Kind regards, 

Gareth. 

Thanks Gareth.

Assume you mean thermostat for the heater matrix?  I've changed the coolant sensor so know that's working now.  

Am I wrong in my thinking that the lack of engine temp would impact whether hot air comes out the blowers, or would a faulty blower thermostat impact what the engine temp sensor is showing?  

[Andrew Bell]

3 hours ago, jasonj said:

Hi Andrew, 

1: check Water Pump

2: Thermostat...... This  could be stuck . 

3: Heater Matrix . for Air ... Jasonj

I'm fairly sure water is circulating as I can feel various hoses either side of the rad getting hot and the coolant reservoir builds pressure, so would that indicate the water pump is working?

[Magnet]

Hello Andrew, 

It’s the thermostat for the whole engine coolant system. Yes, as stated, unless the coolant is up to 90 degrees, you aren’t going to get maximum warmth out of the heater.

Kind regards,

Gareth. 

[7-up]

In general, if you have no temp reading on the dash, the gauges sensor is usually at fault and easy to change. The other known culprit on some wrong gauge displays can be curcuits behind the main instrument cluster.  Following others advice I took mine apart some years ago, changing bulbs, cleaning the plastic front and cleaning, checking all manner of lightly corroded contacts, fittings and cables. In doing so you may even find a mouse eaten or chaffed though  cable, the latter being the culprit in my daughters car's non functioning horn cabling in the dashboard ....which was surprising as her car is  low mileage and immaculate.  Some  work on cleaning / checking the audi's cables and connections has definitey enhanced many things. 

[7-up]

If the gauge is reading,  it may still show the wrong temp if dirt or damage is causing resistance in the electrical cabling. In general I've found that even before my 2.6 gets to 90 degrees the heater gives me loads of warm air.  The car does however take much longer to warm up in slow town driving on a winters day.   I think others have hinted that the valve allowing hot engine water to the heater matrix, when you want interior heat, can fail which I agree with. The old British classic cars could just need the valve cleaning out, but the Audi may be different. As always use the screwed in bleed terminal  in the steel water pipe, looking front to rear of the car, at the back right of the engine, to check there's no air lock denying water flow to the heater matrix, which I've seen happen once, because this bleed point is almost hidden.