It has been a cold winters day and it felt particularly cold in the JGS4x4 workshop today. So it was rather surprising to see one of the Discovery 3’s that we had in for an automatic gearbox flush had an abnormally high transmission fluid temperature.
Before carrying out a gearbox flush we always do a full diagnostics check to make sure there are no electrical or mechanical problems with the gearbox as a fluid change cannot fix electrical or mechanical problems. Part of this diagnostics check is to check the ATF fluid temperature, as we have to carry out the flush and level check within certain temperature parameters. At 89 degrees it was a bit of a concern, the customer had only travelled 40 miles on it was a cold day so the gearbox fluid should not have been that hot.
A quick check soon pinpointed the problem!
The owner had used his Discovery 3 for what it was designed for, he had been off-roading in the summer and had been in some deep water, not a problem as this is what they are for but unfortunately, the dirty water had partially clogged the radiators impeding the cooling performance of the coolant, air con, ATF, PAS radiators and the intercooler.
We gave it 20 minutes to cool down a bit, carried out the flush and advised the owner to spend an hour or so cleaning the cooling system thoroughly. The biggest killer of automatic gearboxes is overheating, make sure your cooling systems are in good, efficient working condition and always wash the radiators thoroughly after off-roading or wading in deep, dirty water.