Coolant Leak - Temperature Sensor

Dear fellow enthusiasts,

After some searching, I thankfully found a leak (0.6 liters of coolant loss in 2 weeks) - it's coming from the temperature sensor (on the right side of the engine, roughly at the level of the vacuum pump - two levels down). Hopefully, that's it.

Here's a photo and the question: What is the correct part number for an ALH engine, manufactured in 1998?
059 919 501?
Should I install a new sensor, or should I just replace the seal and this clamping bracket?
Is this a common type of leak? I read somewhere that someone else also experienced a leak in the same area, where a coolant hose had swollen internally to the point where very little could pass through – which was apparently not visible from the outside.

I am, as always, very grateful for any responses and the opportunity to learn more about my vehicle...

Best regards.

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Hello,

Yes, 059 919 501 is the correct VAG part number. The sensor is sealed with a slightly thicker rubber ring to fit into the housing, and this ring may be defective or crumbling.
Before installing the new sensor (a new sealing ring is usually included), the sealing surfaces should be inspected and, if necessary, cleaned.

Best regards, Rainer.

hello rainer,

Okay, thank you very much. I'll get that sorted out for now.

Regarding your tip: You probably wouldn't get a very good view that way. It would likely only be possible if you drained the coolant beforehand and then used a mirror to look.

Best regards.

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... and you have entered the correct term - dual temperature sensor. I've learned something new.

little wrote:

Regarding your tip: You probably wouldn't get a very good view that way. It would likely only be possible if you drained the coolant beforehand and then used a mirror to look. Best regards. little

It's doable if you're quick, but only a small amount of coolant will leak out. In your case, I would recommend taking a closer look at the sealing surface and draining a little coolant beforehand.

Best regards, Rainer.

Okay, it's installed. Quite a bit of water and G12 coolant came out - I'd estimate about a liter to a liter and a half. Maybe because the Golf was lifted at the front - it was caught, so no problem.
Interestingly, the old seal still looked good, although it was a bit thicker and less flexible.

It seems to be contained now, but it will be closely monitored for the time being.

Best regards to you, Rainer, and everyone else, and have a great weekend.

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