Car takes ages to warm up, thermostat replaced (1.4L Petrol BBY)

a2a

a2a

Member
Hi there,

Long time lurker, first time poster! I'm a fairly proficient DIY spanner-er, but new to A2's 😁

I bought my 1.4L Petrol A2 a few months ago, and straight away noticed it took longer to warm up than my other cars. At 10°C it would take 7 miles / 15 mins to warm up (mostly motorway). In stop/start traffic it would take an age.

Last week (when it was warmer than today, still 10°c or so) I noticed it still hadn't warmed up fully to 90°c after 40 mins in traffic. Furthermore, I could influence the temperature gauge between 80°C and 90°C by turning the interior heater on and off!

Fairly confident a new thermostat was required, I fitted one today along with a temp sensor for good measure. I noticed:
  • It'd already been changed before with a non-genuine one
  • The existing one didn't seem to be stuck open in any way and behaves normally when tested in a pan of water on the stove
  • Fitting the new thermostat doesn't seem to make any difference 🤔

As I brought the car up to temperature on the driveway with the new stat, it behaved like coolant was getting into the radiator still:
  • Both top and bottom rad hoses were warming up to the touch (the bottom hose cooler, naturally) before the gauge had even moved from 60°C
  • At 70°C, the hoses were quite warm, and the radiator too
  • By 80-90°C, once the 82°C stat should be open, there wasn't any noticeable jump in temperature that I could feel on the hoses and rad (which I would normally expect once the stat has opened)
Has anyone had this before?

Is there a way water could get into the radiator when the stat is closed?

Cheers,
Chris
 
BTW, I have a fully registered VCDS Lite. If given the steps to follow I could dig out any helpful information.
 
a2a said:
Hi there,

Long time lurker, first time poster! I'm a fairly proficient DIY spanner-er, but new to A2's 😁

I bought my 1.4L Petrol A2 a few months ago, and straight away noticed it took longer to warm up than my other cars. At 10°C it would take 7 miles / 15 mins to warm up (mostly motorway). In stop/start traffic it would take an age.

Last week (when it was warmer than today, still 10°c or so) I noticed it still hadn't warmed up fully to 90°c after 40 mins in traffic. Furthermore, I could influence the temperature gauge between 80°C and 90°C by turning the interior heater on and off!

Fairly confident a new thermostat was required, I fitted one today along with a temp sensor for good measure. I noticed:
  • It'd already been changed before with a non-genuine one
  • The existing one didn't seem to be stuck open in any way and behaves normally when tested in a pan of water on the stove
  • Fitting the new thermostat doesn't seem to make any difference 🤔

As I brought the car up to temperature on the driveway with the new stat, it behaved like coolant was getting into the radiator still:
  • Both top and bottom rad hoses were warming up to the touch (the bottom hose cooler, naturally) before the gauge had even moved from 60°C
  • At 70°C, the hoses were quite warm, and the radiator too
  • By 80-90°C, once the 82°C stat should be open, there wasn't any noticeable jump in temperature that I could feel on the hoses and rad (which I would normally expect once the stat has opened)
Has anyone had this before?

Is there a way water could get into the radiator when the stat is closed?

Cheers,
Chris
Click to expand...

I have had this before with our AUA, which uses the same thermostat arrangement. Firstly I put a FEBI Bilstein replacement in, using the same logic that you had. The thermostat was the original cylindrical form. However the clue was that the top and bottom hoses both warmed up to the same temperature, meaning that the thermostat was somehow being bypassed.

In the end it turned out the the top housing was distorted, presumably by heat and the pressure of the thermostat actuating rod pushing on it. I then purchased a new stat again along with the new outlet cover, and noted it has a revised design with much more ribbing to prevent it distorting.

Things still didn't go right, because the locating recess in the lower housing must have collapsed whilst I sat the new genuine Audi thermostat into the housing, leading it to move sideways and deeper into the housing. The result was the same, in that it didn't warm up again, this time never getting to temperature at all.

When I took the thermostat housing off yet again, the thermostat had slipped sideways into the housing. Just to add insult to injury, the actuating rod in the thermostat had been able to fully extend without restraint, which had destroyed the brand new Audi (£40) thermostat.

The solution was to buy a brand new Genuine Audi housing complete with thermostat, along with the Death Pipe and retaining clip and replace the whole flaming lot. When replacing the Death Pipe, the water pump end of the original was falling to bits. I suspect its demise was helped by some corrosion of the cylinder block around where the pipe enters the back of the water pump housing.

Now around £200 lighter for the parts (two dead quality thermostats, one outlet cover, one Death Pipe and clip, one new thermostat housing assembly complete), the thermostat was working perfectly and the car warms up fully in around 1.5 Miles.

I do have pictures of the old housing, which I will upload when I get the chance. Out of interest, the new genuine Audi housing uses a normal thermostat, hence there is no pressure on the top cover any more.
 
This is interesting Mark!

Mine uses a more traditional disc-style thermostat (I bought both types, but the black plastic type wasn't suitable).

I couldn't get the thermostat housing lid to go back on squarely - with old or new thermostat - but it didn't leak, so I didn't worry about it.

It's only slightly out of kilter, but I wonder if it's causing some coolant to bypass the thermostat?

A new "Topran" housing is only £30, so easy to try.
 

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a2a said:
This is interesting Mark!

Mine uses a more traditional disc-style thermostat (I bought both types, but the black plastic type wasn't suitable).

I couldn't get the thermostat housing lid to go back on squarely - with old or new thermostat - but it didn't leak, so I didn't worry about it.

It's only slightly out of kilter, but I wonder if it's causing some coolant to bypass the thermostat?

A new "Topran" housing is only £30, so easy to try.
Click to expand...
Hi A2A, when you say the black plastic thermostat wasn't suitable ... I think you've read my post already and realise that the cover holding it in place is specific to the type, whether it's the old type or newer cartridge ... I'm pretty confident that the BBY would have had the cartridge from new, according to what Audi Service told me!
I've had no problems with the Topran housing installed with genuine Audi cartridge thermostat and matching cover.
I drove it to band practice last night at 2 degrees outside and was blowing hot after three miles ... maybe the system works better with the cartridge type?
 
As an observer, it doesn't seem logical for the thermostat housing to be compatible with both types of thermostat. They look quite different.
Mac.
a2a said:
BTW, I have a fully registered VCDS Lite. If given the steps to follow I could dig out any helpful information.
Click to expand...
You could log the coolant temp, over a journey, we'd then know exactly what is, or isn't happening.
Group 001, I think.
Mac.
 
Tomscar said:
I'm pretty confident that the BBY would have had the cartridge from new, according to what Audi Service told me!.... Maybe the system works better with the cartridge type?
Click to expand...

Yes I'm beginning to think so too!

I've ordered a complete Topran housing (£30) - as one of the holes in the plastic housing was starting to strip - along with the cover to suit the cartridge type thermostat (only £3.32 on Autodoc!) and already have both thermostat styles, so will experiment with all combinations when they arrive and report back 👍
 
Last edited:
PlasticMac said:
As an observer, it doesn't seem logical for the thermostat housing to be compatible with both types of thermostat. They look quite different.
Mac.
Click to expand...

Yes I agree, I think my housing cap must have been swapped at some point, along with the thermostat.


PlasticMac said:
You could log the coolant temp, over a journey, we'd then know exactly what is, or isn't happening.
Group 001, I think.
Mac.
Click to expand...

Good idea, I'll have a poke around 👍
 
PlasticMac said:
As an observer, it doesn't seem logical for the thermostat housing to be compatible with both types of thermostat. They look quite different.
Mac.

You could log the coolant temp, over a journey, we'd then know exactly what is, or isn't happening.
Group 001, I think.
Mac.
Click to expand...
Hi Mac, I can confirm that the Topran housing is compatible with both types of thermostat and dependent on using the corresponding cover. I have a thread on here somewhere with pictures, if I can find it I will repost.

The molded part within the housing that holds the cartridge type thermostat in place is simply redundant when the traditional metal disc type is used.

The original Audi housing was exactly the same configuration on my BBY as the Topran but might be interesting to find out if the AUA has the internal molding. Not sure if the Audi Service department were just spinning a yarn but they have said that the BBY would have been the higher temperature cartridge type.
 
a2a said:
Yes I'm beginning to think so too!

I've ordered a complete Topran housing (£30) - as one of the holes in the plastic housing was starting to strip - along with the cover to suit the cartridge type thermostat (only £3.32 on Autodoc!) and already have both thermostat styles, so will experiment with all combinations when they arrive and report back 👍
Click to expand...
All I can add is that I didn't use the thermostat or cover that came with the Topran housing ... the original Audi parts had lasted for around eighteen years from new and for peace of mind went with genuine Audi again ... surprisingly not that expensive from a Skoda dealership!
 
PlasticMac said:
Is it an AUA to BBY change over thing, where early BBYs had some AUA parts, such as the the housing, but when you order a replacement you'll get the BBY part?
Mac.
Click to expand...
Could be Mac and seems a reasonable assumption ... although, give Audi their dues, any parts I've ordered from the dealership were specific to my chassis number, certainly here in Belfast Audi.
Regarding thermostats, maybe there's some link to the computer ... 83 degrees opening and my heater didn't get hot and 87 degrees it did.
Now my car is so old, I'm happy tinkering and learning, using genuine parts where necessary but willing to give other parts a go also, based on the shared knowledge of this club.
Best motor based club out there ...
 
Last edited:
Tomscar said:
Could be Mac and seems a reasonable assumption ... although, give Audi their dues, any parts I've ordered from the dealership were specific to my chassis number, certainly here in Belfast Audi.
Regarding thermostats, maybe there's some link to the computer ... 83 degrees opening and my heater didn't get hot and 87 degrees it did.
Now my car is so old, I'm happy tinkering and learning, using genuine parts where necessary but but willing to give other parts a go also, based on the shared knowledge of this club.
Best motor based club out there ...
Click to expand...
A log of coolant temp is the only way to find out.
Get a toasty FSI, nice hot coolant ...
Mac
 
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