I hope that it is just a water pump gasket as suggested. I had a less than typical experience with the V6 in my lexus where I developed an external leak (significant drip) from the block face where it meets the head. No water in oil, temperature rise at idle-normal going down the road, and steady loss of coolant.

It turned out to be a blown head gasket that resulted only in an external coolant leak. This was the infamous toyota iron block/aluminum head.

I would check for any signs of water in the oil and take the radiator cap off while running to check for bubbles. Or you could get a radiator pressure tester to pump up the system to provoke a leak.

Just my thoughts and I hope I'm wrong. Good luck!

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'82 240D Euro 68K and growing