Ali - After some searching I stand corrected on the transmission fluid change interval - at least with respect to what this forum is recommeding. My info was from a knowledgeable source in MBCA. I stick to my personal recommedation. Even though the fluid is expensive, a changeout is cheap in the overall scheme of things. Just my opinion.

However, I am not a fan of infared units. I'm in the marine industry. We have used infared thermometers for years when trying to confirm readings from various temp sensors. We have used units from Raytek and Fluke. We have come to the conclusion that most of the affordable units are too inaccurate to be of much value. I am not sure why. My guess it is because of outside factors as the basic accuracy is usually acceptable. We only use them for a general check (trending, for example) or where no sensor is fitted. We do have a contractor that performs regular thermography on our switchboards and they use infared cameras, but the cost of their equipment is far too high for our purposes, as it would be for a DIYer for a transmission fluid change. I have a Fluke 61. The only time I used it for a similar proceedure was on a VW Passat. My Fluke was some 30 degreesF different from the reading I got from my VAG-COM program (which reads the transmission temp directly from an internal sensor in the same way the M-B dealer equipment does).

I am confident in the work around procedure. While the exact temp is not checked, the same level is established after service as before at similar temps (cold start and 20 mile drive). The fluid will expand the same amount. The point is to match the dipstick readings you get before and after, not to fill the trans to the 80 degreeC marks if it was not there in the first place. Provided the transmission was at the correct level in the before, it will be after service. Plus, measuring the exact quantity of fluid drained is a confirmation. In my opinion, the idea that the level must be so very, very precise does not dovetail with the fact that the 80 degreeC range on the factory dipstick is 11mm wide.

I'm a bit surprised at the 110 degreesF. After all, the transmission cooler is in the radiator, surrounded by the engine coolant, which should be at around 180 degreesF and, to my knowledge, there is no "thermostat" that bypasses the cooler until a preset temperature. I'm surprised at what appears to be a lot of radiant loss over of couple feet of connecting tubing.