Why Should I Have My Saildrive Diaphragm Replaced?
Is a pre-cursor question we at Motortech often hear; closely followed by the statement – “it looks fine and doesn’t leak”. To accurately answer, let’s delve into the engineering a little more deeply….
To know why we should change it, we must first understand what it does. The saildrive diaphragm serves 3 main purposes. First, and foremost it is a water seal between the inside of the boat (the part we want to stay dry) and the outside of the boat (the part we don’t mind getting wet). Secondly, it serves to isolate and absorb a large amount of vibration from the engine for greater comfort on board. Thirdly, it, along with other gaskets and seals keeps oil inside the drive.
Due to the location of the diaphragm and it’s typical use, it has a hard life. Oils, antifreeze, sea-water, marine organisms, temperature extremes and vibration attack it constantly. Groundings, fouling, and gear shifts require it to flex and move, sometimes violently. And all the while we expect nothing less than 100% success from its service. It is an un-enviable job!
So back to the original question we are asked. Volvo Penta guidelines recommend that replacement is carried out every seventh year. Volvo Penta carries out a huge amount of research and development continuously on their products in service, and we will always advise that the manufacturer recommendations are followed.
Why if it looks fine? Because it’s what you can’t see that tells the real story! To the right is a photo of a clamping plate taken from a saildrive which recently had the diaphragm replaced by us. The diaphragm was nearly 10 years old, and looked in great condition. Unfortunately, the clamping plate had been attacked by sea-water and had started to corrode on the sealing surface, adding at least £200 to the customer’s final bill. 
The corrosion to this plate has not been occurring for too long (possibly only a year or two), which indicates that had the manufacturer’s guidelines been followed this cost could have been avoided. More importantly, if some ‘internet forum’ advice was followed by this customer (some forums offer advice to wait for 15-25 years!) then there is the very real and possible risk that this could have failed catastrophically at sea, causing failure of the saildrive, a major flood or sinking.
Another word of warning! We also advise all of our customers to check their insurance requirements for this service. An insurance company may refuse a claim if the failure is proved to be due to neglect, or failure to follow the manufacturer’s recommended service intervals.
For Power and Sail with Peace of Mind…. Your Volvo Penta Centre of Choice on the South Coast
For your FREE, no obligation Estimate call our service department on 023 92201171 or email info@motortechmarine.co.uk
