using a engine watchdog with the thermocouple on the drivers sise of the engine at the front .Normal driving @83-86 towing a 5m boat upto 92 we did go higher until i replaced the rad and thermostat with mazda original units,

if you contact any wurth rep www.wurth.co.uk they sell the dye and uv light etc you need it is also available for oil and air con also one to find water leaks in roof etc

are you putting them in the rear springs?

i see the 80777 are for the front of the vehicle is that where you fitted them or did you use them on the rear

I had the usual problems with my bongo.
Random overheating
Water loss.
I replaced the thermostat and hey presto no problems now.The engine watchdog rarely reads a temp over 92 degrees.
95 towing a boat up hill.