Audi A8l w12 coolant issue

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10-07-2022, 11:35 AM

Kaissias

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Audi A8l w12 coolant issue

So I'm helping out a friend which has purchased a 2002 A8L w12 that was really neat and looked to be very well kept.

the car had a cooler failure which was repaired with the previous owner and the coolant did have signs of sludge in the system which we have flushed and got the system clean.

Which brings me to the issue at hand... so basically the car starts fine bu it shows the red coolant light that indicates its low on coolant but its not. It drives very smooth without any issues. But when you park it while its hot and switch it off, it fails to start back on. It cranks very slow as if the battery is low. But if you leave it to cool over night it starts fine. Checked the alternator: charging fine. Battery: replaced and new... same issue..

Also deffinitely worth noting is that if you drive the car for extended periods. low oil pressure light will come on although the engine stays extremely smooth.

At this stage, we thought to ourselves that the previous oil cooler failure might have caused some oil build up in the system which was preventing the coolant system from properly circulating and the engine to overheat but not show on the dash because the coolant temp sensor was not reading the hot coolant due to lack of circulation.

So here is what we did and i wish some one can point out if i made a mistake of forgot something:

-we properly flushed the coolant system over several stages untill it became crystal clear
-we bled the system from the heater lines and from the thermostat( im not sure if there are other points to bleed)
-we removed the radiator and sent it off to be tested if it was clogged and it was in good shape.
- we replaced the water pump

as said, car does not overheat on the dash but the low oil pressure light and extreme load to start the car whil hot really convinces me that the engine is indeed overheating.
i did run a live data on a universal scanner and check the coolant tempurature sensor reading and it showed to reach 117°C (240°F) which is a deffinite red flag. But the issue is that i don't have a VCDS so i am not absolutely sure that what the scanner is telling me is accurate.

I am now stuck scratching my head and i wonder if a similar situation has been experienced by any one hear or if someone can point me in a direction that i might have forgot.

thanks!!