Cooling problem

[Vilhelm]

Hi guys,

Long time since I logged on here last time. Good to be back

I got a new car. Audi A8 with an RS2 engine. Dynoed 520HP @ 1,8 bar. Built by Jonus.

The problem:

Car gets up to temperature @ idle. It shows just under 90 degrees (usually) while idling. Once the car starts moving the temperature drops to 70ish degrees.

The cabin heater works great when it's at idle and shows 90 degrees, but it blows cold after a bit of cruising (when the temperature goes down).

I think the problem is the thermostat, but something weird has happened before:

Sometimes I let the car idle for a while (cold start) before I start driving, and the temp shows 100 degrees, but the heater won't blow hot air. When I start driving the heater works, and it works after that if I let it idle.

Does this sound like a thermostat problem?

Thanks guys

[Jamo]

Sounds like an air lock in the heating system, if the thermostat was stuck open the car would have a hard time warming up.

Did you bleed the system with the heating on full blast and use the bleed screws on the rad and the heater matrix hose?

[Vilhelm]

Sounds like an air lock in the heating system, if the thermostat was stuck open the car would have a hard time warming up.

Did you bleed the system with the heating on full blast and use the bleed screws on the rad and the heater matrix hose?

Thanks Jamo for the suggestion. I'll give it a try, but the builder said he had done this several times before.

I'll post a reply once I have done this

[Jamo]

He's probably only done it on the rad bleed screw only and not the bleed screw by the bulkhead:

Make sure the coolant tank is full and open the valves at position 2 and 3. Start the car and leave to run upto temp then turn on the heater to full/hot. Keep topping up the water to the right level(max) and wait for the air to disperse from the top of the rad. (water flow will be constant). Close this and do the same thing for the heater hose at the rear of the engine compartment. Check the heater is blowing hot.

I make sure the fan has kicked in twice during the bleeding

[Vilhelm]

Thanks again Jamo for the detailed explanation. I have an aftermarket radiator. I checked and it didn't seem there was a bleed valve for the radiator. I will try with the bleed valve on the heater hoses. Hopefully I can get it done today I'll keep you guys posted.

[Vilhelm]

Here is a pic of the bleed valves:

I'll post better pics later (when my friend gets back from work). We tried the bleeding of the heater hoses (marked in red), but once we unscrewed the bleed valves coolant was pouring out, didn't seem like there was air there.

Should we just let the coolant pour out of the bleed hole (many liters of coolant) while putting coolant in the expansion tank? I thought air would always come to the top of the system?

Today on my way to work the temp hit 100 degrees, and the heater didn't blow hot air even though I was driving. The heater slowly started just as I turned into the parking garage at work. Very strange.

[gnutz2]

I would make sure your temp guage is reading correct with an auxilary guage (theres no point in chasing your tail) .

But if the heaters start to cool down when cruising it sounds like the thermostat is stuck open (or has been removed which is even worse).

Is all the plumbing piped up as on a standard car?

I would avoid thrashing the car until you get it sorted.

[Vilhelm]

I would make sure your temp guage is reading correct with an auxilary guage (theres no point in chasing your tail) .

But if the heaters start to cool down when cruising it sounds like the thermostat is stuck open (or has been removed which is even worse).

Is all the plumbing piped up as on a standard car?

I would avoid thrashing the car until you get it sorted.

Thanks gnutz,

I did test that the guage is correct. I opened the expansion tank lid and watched the guage (when car was at idle - fans turned OFF). Once it reached a bit over 100 on the guage the coolant boiled (not the most graceful way to do it though )

The temp is stable @ idle/heavy traffic with fans running. It stays right at 90 degrees. When I start driving the temp goes down to about 70-90, depending on if I drive it in the city or high way.

If the heater always worked (when temps are up) it would most defiantly be the thermostat, but considering that the heater won't work at times (even when the temp is showing 100 degrees) it could also be something else.

I have no idea if the hoses are the same as stock, but I would imagine they are. I'll get up some more pictures soon

[gnutz2]

Check for bubbles in the header tank when revving the engine hard. I've known cars run for months with a leaking head gasket and it would explain air in the system.

Does the car get up to temperature quick?

1st Job is to change the thermostat then.

[Vilhelm]

Thanks again Gnutz

I'll go ahead and do the rev-test, and if I don't see any bubbles I'll change the thermostat. I'll keep you guys posted

[Vilhelm]

It was indeed the thermostat. I bought a new thermostat and coolant, and dropped off the car at www.s-sentrum.no. Works fine now

Thanks for all the advice guys! Appreciate the help.

[20vQC]

a bit off topic but... an A8 with a AAN?! WOW! I like it a lot!!! beautiful!! pls more pics!

[20vQC]

sorry... not AAN but adu. 20VT anyway!

[Vilhelm]

a bit off topic but... an A8 with a AAN?! WOW! I like it a lot!!! beautiful!! pls more pics!

http://www.s2forum.com/forum/showthread.php?p=476664

There you go