Why CVT gearboxes need oil changes

Posted on November 1st, 2021 by GEM Motoring Assist

At GEM’s technical division, we are sceptical of car manufacturer claims that certain parts of a vehicle never require oil changes. The statement ‘sealed for life’ tends to be used but closer analysis reveals the interpretation of ‘life’ to differ. One car manufacturer I spoke with claimed it to be seven years – a figure, incidentally, that is less than the age of an average car currently on UK roads…

However, regular oil changes benefit transmissions especially and this blog’s focus is on CVT, AKA Continuously Variable Transmissions. This is a type of automatic gearbox that contains a drive belt sandwiched between two pulleys. Initially, these were rubber belts that were used by DAF, a small Dutch manufacturer of quirky economy cars, which Volvo took over in the mid-1970s.

Yet, CVT has matured and the rubber belts are now made from metal and are enclosed within a transmission case. A variety of manufacturers have used CVT gearboxes but the Japanese brands are the most dedicated to the technology. Sadly, the CVT is not the most reliable gearbox available, Toyota applications excepted.

Many of the problems are caused by the oil and the interaction between the metal belt and pulley. Heat is the first issue – CVTs tend to run hotter than conventional automatic gearboxes, which hastens oil degradation. Additionally, the belt drive creates many minute metal fragments that can circulate around the transmission with the oil, contaminating other parts, such as the valve body.

Therefore, consult your handbook for CVT oil and filter change intervals. Should one not be quoted, several transmission specialists, with whom we spoke, recommend

30,000 miles as a sensible interval. The operation should involve not only changing the oil but also removing the sump, replacing the filter(s) and cleaning any accumulated swarf from the magnetic washers inside

If your car has exceeded this mileage and have not had a CVT oil change, it may be a good idea to obtain quotations for the work.