FL S8 AQH Overheating issue

[SilverS8]

My FL S8 overheated yesterday when in slow traffic.
It showed 110-120.
When driving it heats up normally and it has taken apx 25-30 min before it passes 90 deg(most likely because i then hit traffic) This is with fan at 75% and max heat on. Took about 15 min when climate on "Auto" and set to 22.

Observations:
- Top of radiator luke warm
- Lower 3/4 of the radiator is cold.
- When idling it won't pas 105 deg with climate on max speed/heat
- When driving at apx 60mph it reach 110-115 before el.fans reduce it to 100-105, Climate on max speed/heat does not manage it to stay under 105 deg like when idling.
- Temp hits 90 deg and stays there for 5 apx 5 min before increasing
- The viscous fan iirc used to operate different, if idling for a while(at 90 deg)and revving you would easily hear it move air(not sure if this spins quicker when hot?) that sound is gone, but it still moves
- The climate produces plenty of heat
- No fault codes in VCDS
- Temp gauge readings match the VCDS reading.

Questions:
- Would there be heat in the climate if waterpump is gone?
- Would a stuck closed Thermostat allow water to flow to the climate?
- Would a stuck open thermostat cause an overheated engine?
- Could i Force the extra electric fan to start in VCDS(not just output test)
- The carrot test, how?

Car has 151000 miles on it. Cambelt/Waterpump and all was changed at apx 125000 miles at Audi(PO)

No time to dismantle the car before Christmas

[Mechcanico Lee]

The fact that you have good in car heating says the water pump is working

If the thermostat is closed you will still get heating in the cabin

A stuck closed thermostat will cause over heating

A stuck open thermostat will cause the engine not to get up to temp (over cooling )

Warm or hot top rad hose and cold bottom hose .....classic thermostat not opening symptom .... can also be blocked radiator .....replace thermostat first then see if bottom hose gets warm

"Force the fan to work ".... fix the initial fault , forcing the electric fan to work is a band aid on the original fault

[SilverS8]

Originally Posted by Mechcanico Lee

The fact that you have good in car heating says the water pump is working

If the thermostat is closed you will still get heating in the cabin

A stuck closed thermostat will cause over heating

A stuck open thermostat will cause the engine not to get up to temp (over cooling )

Warm or hot top rad hose and cold bottom hose .....classic thermostat not opening symptom .... can also be blocked radiator .....replace thermostat first then see if bottom hose gets warm

"Force the fan to work ".... fix the initial fault , forcing the electric fan to work is a band aid on the original fault

A thermostat then

Managed to drive the 20-25 min to work this morning without it exceeding 90 deg (with max heat on the climate)

From what i have found, the 40V engines really requires timing belt removal in order to change the Theromstat, is that correct? I have yet to find any info on the AQH engine for either timing belt or Thermostat.

I'm sure ElsaWin has a write up i need to look at.

[Adrian E]

Originally Posted by SilverS8

A thermostat then
From what i have found, the 40V engines really requires timing belt removal in order to change the Theromstat, is that correct?

I think you're right - it's what ElsaWin says, although I suppose it might be possible to access it without full removal?

[laketahoequattro]

No it is completely possible to replace the t-stat by just moving the belt off the left cam "facing car" sprocket enough to unbolt the thermostat housing and replace the t-stat. I have done this twice successfully.

[Adrian E]

Originally Posted by laketahoequattro

No it is completely possible to replace the t-stat by just moving the belt off the left cam "facing car" sprocket enough to unbolt the thermostat housing and replace the t-stat. I have done this twice successfully.

That's near enough removed though really if you're thinking in labour bill terms, assuming you're paying somebody else to do it? To get to that point must involve a fair bit of dismantling....

[SilverS8]

Originally Posted by laketahoequattro

No it is completely possible to replace the t-stat by just moving the belt off the left cam "facing car" sprocket enough to unbolt the thermostat housing and replace the t-stat. I have done this twice successfully.

I did see see a youtube movie showing the same. The guy there had removed one of the small rollers to be able to move the belt a bit more.

With labor here at local shops running £100 per hour and Audi £160 per hour, i do all the maintenance my self Think i'm gonna try changing the thermostat first and see how she responds.

Just finished a total overhaul of brakes,calipers, rear dif, control arms, gearbox filter & oil, inner/outer tie-rod, and so much more back in August so was hoping for a long break now