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

[SilverS8]

Update.

Just removed all covers and trying to figure a solution to gain access to the thermostat without removing the tb.

First off, after watching a clip on youtube were the guy states there is a certain point(when turning the engine) that gives the tb less tention, I started turning to find this spot. However that came after 1/15 turn on the crank, and that seemed fine enough intill i cobtinued to turn and for what seems like every 1/8 turns it keeps changing between loose and sick tight. At the same time the waterpump wheel is not moving everytime i hit one of those loose spots....

So:

-Does this manual turning reflect how the tb is actually tentioned when engine is running? or will it for some strange reason be more tentioned ?
-anyone manually turned their FL S8 and have comparrison?
-Should i just continue and do the thermostat or should this loose/tight be investigated further?

Any suggestions would be appreciated

[SilverS8]

Well... That seems to be it..

As mentioned above i have only handcranked the engine to find the socalled loose spot..

After last post i stupidly started the engine with the idea of monitoring the waterpump, however just as it started it sounded immediatly like the tb was a couple of tooth off.. (loud valve sound) It ran maybe dor 1 sec max before i turned it off....

As f now the tb is tight all over but i'm afraid there might be some bent valves..

Is there any way to check timing without the cam-locking metal tool?

I need a beer..

[MikkiJayne]

Mine had the belt just flapping about because of the failed tensioner and doesn't *appear* to have bent any valves (no visible marks on the pistons). Could yours have just been chain tensioner noise?

I have a brand new engine waiting to go back in mine - I will check how the belt behaves on that and report back. I'll not get to it until Tuesday though.

You can visually check the timing to see if it's close. Turn the crank so that the notch in the pulley lines up with the mark on the lower belt cover (about 1 o'clock). The four holes on the cam shafts should all be horizontal - measure with a straight edge, or even a bit of string. Obviously you can't set it like that, but you can tell if its wrong.

I can see the argument for the belt going slack - the roller cam followers allow the cams to jump around when they are coming off the lobe, compared to tappets which don't behave like that. As the cam jumps round it could pull the belt tight in places and loose in others. Turned by hand the tensioner may not be able to accommodate this. If it does behave thus, I can't see how it could possibly do that with the engine running without tearing itself to bits. Rotating inertia, oil pressure, etc should see to it running smoothly. Of course all of this is conjecture until either I have a look at my factory engine or an expert chimes in! I would not claim to be an expert on the 40V.