Leaking Head Gasket symptoms?

[iguana]

Hello i drive a seat leon mk3 cupra ST 2017 i got like 45k miles on it, for some time now my car has been sucking in coolant(not always) and then the warning light comes on. After turning off the engine and waiting a while, it returns to normal, and when I unscrew the cap, it also returns to normal. Also, the tempreture of coolant is always 90, and the oil tempreture stays normal in range of 90 to 115 no matter how i drive. Today I unscrewed the cap from the tank and noticed black floating spots, and I also see black sediment on the edges of the tank. It's not much, as the entire liquid is cream-colored, but it is visible. Is it a gasket problem, or maybe the oil cooler or exhaust gas cooler?

I went to the mechanic, he said it is probably a gasket, I'm going to check it in a few days. Has anyone had a similar problem and could advise?
Just wanna add, that i didn't noticed any visible leaks of coolant.

 

[The-Cupra]

If you unscrew the cap and coolant sucks back in the header tank then it could be head gasket.

The only other thing it COULD BE is a faulty coolant cap. I have seen this before on these cars where the coolant cap was not releasing pressure and it was over pressurizing the coolant system.

Either try a new cap or buy a Combustion Leak Tester Kit

 

[cuthound]

Use this for a cheap, quick and dirty head gasket failed test.

RELD Cylinder Head Gasket Tester CO2 Check Cooling Water Universal All Models | eBay

RELD reaction liquid with a capacity of 100 ml. Cylinder head gasket tester CO2. The entire process takes no longer than 5 minutes and gives you almost 100% certainty that the cylinder head gasket is not broken.

www.ebay.co.uk

• The original cylindrical tester of the reputable brand 'Reld'
• Produced in the European Union. The efficiency is 99.9%.
• Fast and convenient. Most importantly you can check whether the gasket under the head of your car is fully functional without visiting the mechanic.
• If the gasket under the cylinder head looks damaged, you can check it yourself and save time and money.
• Thanks to the universal adapter with a wide measuring range (25-55 mm), we can check among other things: cars, trucks, road tractors, excavators, motorcycles, forklifts.