Remember the oil tank issue we discovered on Mclaren cars? if not the initial story is HERE where we had a car with a hole in the oil catch tank and no real way of understanding how the hole happened?

Well, now we know.

By way of a recap, all Mclaren models have a dry sump oil system and the tank for this is hidden away up behind the firewall and in front of the engine – about as far away from potential impact damage or contact as is physically possible but we had a 12c in with a leak from the tank. One of the downsides of being so protected is that its a proper job to replace it – the engine needs to come out so –  its not a small job, so we wanted to know why the tank had sprung a leak but on investigation all we could see was a neat hole with no under lying cause.

A hole in the side of the tank.

Our best guess at the time was a pulled weld from inside the tank but as this was the only one we had seen we were loathe to cut it up and thought it was a one off, but we warned owners at the time just in case.

Well we are afraid its not a one off, we now have three 12c models here all needing new oil tanks so we decided to cut one of the failed ones open and see what caused it.

Oil tank, cut open to show internal baffles

We were right, inside the tank a spot weld of one of the internal baffles has in effect pulled the aluminium wall in causing a neat square hole where it was fixed, either there has been a thermal difference in how the two materials (aluminium weld or aluminium wall) expanded and contracted or the tank itself has expanded and pulled away from the baffle mount. Either way its a new tank and the engine out to replace it.

Area where the hole appears

This is the baffle and the weld

The offending weld

So, if you have an oil leak from the drivers side front of the engine (just behind the drivers side door) then be prepared for an expensive bill, sorry.