we drove 12 hours motorway speeds from Denmark to Calais (to sail to england) with a weak viscouse coupling and 35 degree summer heat.
the engine, a M20b20 made it but got seeeriously hot, so much so when we got to calais and borded the ferry, i had to leave the bonnet open for the duration of the journey and it was still over 3/4 when we landed,.. then drove 3 hours through london town.
the engine made it, but i advise you check your
Fan coupling / viscose clutch
oil and filter
coolant
thermostat
waterpump