AJM Water Temperature: How to Check & Adjust

While driving at a fast pace, I logged the coolant temperature on a Golf IV with a AJM engine. (The coolant temperature gauge normally shows a reading between 75°C and 105°C, but always indicates 90°C, which is considered normal by VW).

According to VAG-COM, the engine (AJM) can reach up to 98°C when driven at a brisk pace. I have tested this on two Golfs with the AJM engine, and the result is always the same.

I tested it on a 90 HP TDI engine, which only reaches 90°C under the same driving conditions.

However, the thermostat should be the same for both engines, with an opening temperature of 87°C.

Does anyone have any idea, or any comparable values, or is this normal for this engine?