Seat Leon Coolant Leak: 1.9TDi, Autobahn Use

Hello forum,

First, as a newcomer, I'd like to say a few words here:

My name is Benjamin, and I'm actually a BMW driver , but when we were looking for a fuel-efficient and attractive everyday diesel car for my girlfriend, and her brother had a used Leon 1M 1.9TDi that he was selling, we bought the car. It's a nice car, well-maintained, and has been in the family since it was new. Okay, the only 'drawback': the car sometimes needed a little coolant, but this happened irregularly and, according to the previous owner, was not reproducible. In recent years, the car has mainly been driven on country roads and in the city, and the coolant loss was present, but manageable with occasional refills.

Today, my girlfriend drove her car to work, a distance of approximately 45 km each way, mostly on the highway, which it probably hadn't done in a long time. She was driving at about 130 km/h, so not too fast. On the way home, as she was exiting the highway, the red warning light for the temperature gauge came on, accompanied by three beeps. She continued driving home, which probably wasn't the smartest thing to do. When she got home, the car had visibly lost coolant; the expansion tank was empty, and there was a puddle underneath the car. I jacked up the car and could see that coolant was dripping from the middle of the bottom of the radiator, but I couldn't see anything more at first glance due to the plastic fan shroud. There were also clearly visible traces of coolant in the engine compartment, for example, on the plastic cover between the radiator and the engine, and on the battery cover.

According to my friend, the temperature gauge always showed 90°, which is why she still drove home.

Okay, I've done a thorough search, and I'm pretty sure the head gasket is the cause. The vehicle has 260,000 km (approximately 160,000 miles) and it's definitely still the original gasket. What do you think about that?
And why is there such significant water loss? Did the overpressure in the system damage the radiator or any fittings/hoses?
I would be very interested to hear what you, as VAG experts, think about this. I'm wondering why there's overpressure. Could the head gasket be so defective that it's causing significant overpressure in the exhaust, or is it because the engine overheated severely due to a lack of coolant, even though the temperature gauge was showing 90°C?

Is the ARL engine head known for hairline cracks? I would definitely have it pressure tested, but I'd like to know beforehand if I should immediately expect to have to pay for a new cylinder head.
The annoying thing is that the timing belt and water pump were only replaced 20,000 km ago .


Well, it's a shame that I had to join you under such negative circumstances, but I'm glad I found a technically good VAG forum, and I would appreciate it if you could share your opinions about the damage case mentioned above here.

Thank you and best regards,
Benjamin.

First, bleed the cooling system and check where the extreme water loss is coming from. Once that's confirmed, we can take the head off, and then we can talk further. Hopefully, it's just the head gasket.

You'll only get reliable information by taking a closer look. If you're lucky, the only problem is a damaged radiator, perhaps due to a stone impact.