A couple of weeks ago, I was advised by a mechanic to have the automatic transmission of our 1998 V70 XC AWD flushed. The person saying this was adamant that this was necessary. Another mechanic advised that flushing would cost from a minimum of US$120, to $200 if full synthetic lubricant was used and added that flushing might be beneficial though not necessarily essential. A third mechanic advised against flushing in a car that has done 137,000 miles, saying that it would strip the protective patina from the transmission's gears and shafts that will have come from the old lubricant and particulates that developed in it as it aged. He claimed that this could leave a transmission of that age too 'loose', and prone to problems it may not have had before, such as loss of certain gears or even complete malfunction. While this seems odd to me, it is not entirely unlike the way a product like Slick 50 (ptfe) puts a lubricating patina on parts in worn engines, very slightly increasing tolerances, with the effect of 'tightening' the engine up.

It was suggested to me that since we do not presently have any problems with the transmission in our Volvo,we should either leave it as it is, or consider simply emptying, not flushing, the tranny, replacing the filter and then refilling it with new fluid.

I'm not sure what to think, partly because I do not have any experience with Volvo transmissions, an partly because a lot of what I have been told about flushing them does not seem to make sense. Any opinions welcomed.

 

His theory works if the trans in question has been neglected, and the oil has gummed up or turned to tar. What would happen then, if you flushed it, is that all that gummed up oil and tar would break loose and clog all the minute passages in the valve body. Picture a 250k mile trans thats been overheated, and never serviced. If your fluid looks and smells ok, flush it.