charidemou

is it normal to add water 300ml water after 800km driving in very hot weather 38 decrees c ?

Quadcammer

no, you have a leak

thxbuff2001

Check for a leak.

Macster

With the older model cars the cap could leak vapor and the level in the coolant tank would drop over time.

Maybe with the newer model cars too.

With the car cold be sure the cap is securely screwed on and nice and tight. It can take more force to properly tighten the cap than you might think.

I'd remove the cap and rinse it under hot water to remove any residue then be sure the tank threads and the top of the threaded spigot is clean. Be sure the fluid level is at some reasonable level. Note the level.

Install the (now dry) cap and tighten it down.

If you want make a tent of alum. foil. Drive the car around with the A/C off until the engine and coolant are fully up to temperature. Ideally you want the coolant hot enough to cause the radiator fans to run.

Then shut off the engine and carefully open the engine compartment lid -- the fan can come on at any time -- and put the tent of foil over the coolant tank. Close the lid so the engine compartment fan is effective.

Wait.

After maybe 10 to 15 minutes carefully -- the engine compartment fan might still come on at any time -- open the engine compartment lid and check the bottom side of the foil for condensation.

If there is any the cap is leaking or perhaps the coolant tank. These can develop a split along the bottom where the mold seam is and under hot conditions allow some coolant to leak out. But after a while the tank cools and the split closes up.

'course, the leak could be elsewhere. My 996 Turbo water pump developed a leak. But to check for this you need to get the car in the air.

nzskater

Walk around the car slowly after a hot run, smell around each front wheel well, where the air exits from the radiator, and then the engine bay. If you can smell something kind of sweet, you've found the general area of your leak.