For timing chain replacement, they drain all the coolant and refill the same after the work is done. When coolant is refilled, there are airgaps in the coolant lines and the air gaps are removed only when the Engine fully heats up. Conclusion is that coolant level is expected to go down after Timing chain replacement, just pick up a coolant bottle at the SC adn refill and monitor for the next week or so. If coolant level goes down again, it's a leak. If it stays intact, you are all set. If the SC is far away and you do not want to go back, go to a nearby battery shop and pick up a bottle of distilled water and fill in the coolant reservoir, absolutely no issues with that. Hope that clarifies.