Re: My Prestige
Posted: Sun May 17, 2009 9:59 am
Hi All
I think it is a matter of luck on how the car has lived. I do not subscribe to the dipping the rear in the sea theory as a main cause mind.
The subframes are made from plain steel and not galvanised so are much more at risk to road salt corrosion than the XM car body.
The top of the front subframe under the radiators can be well gone with nobody noticing. The rear end is usually intact with paint finish as it left the factory due to regular supply of oil from most engines. Only a few Mk2 models got the fibre undertray but on those that did most have problems. Citroen used open cell foam sealing strips to air seal to the subframe and these just suck up and retain water making sure rusting can start and is then kept going as fast as possible. At the rear a quick look at a few spare wheel carriers (also not galvanised) shows what a nasty environment that area is for exposed steel. The thinner the steel section the faster it rusts away. Citroen used thinner steel plate on the Mk2 carriers which is why most are far worse. The rear subframe and the carrier sit in a large recess under the car. One of the few parts of an XM body that are not fully air smoothed. This will generate low pressure and eddy currents trapping a proporting of the air stream with all its muck, salt and water encouraging condensation on all the exposed steel. The XM Estate sufferes even worse just because the recess is quite a bit larger. The thinner steel components are most at risk in this environment so it is the thin pipe work on top of the main tube and the thinner plates at the lower back end of the rear subframe that really can get hit by rust.
If the car was always put into a dry warm ventilated garage any water dried off quickly preventing the rust process getting underway. If it reqularly sat outside it was probably damp underneath and gently running the rust process for at least half the year. These are extreams but I estimate that my outside car will have suffered about 20 times the rust damage that the garaged on will.
John
I think it is a matter of luck on how the car has lived. I do not subscribe to the dipping the rear in the sea theory as a main cause mind.
The subframes are made from plain steel and not galvanised so are much more at risk to road salt corrosion than the XM car body.
The top of the front subframe under the radiators can be well gone with nobody noticing. The rear end is usually intact with paint finish as it left the factory due to regular supply of oil from most engines. Only a few Mk2 models got the fibre undertray but on those that did most have problems. Citroen used open cell foam sealing strips to air seal to the subframe and these just suck up and retain water making sure rusting can start and is then kept going as fast as possible. At the rear a quick look at a few spare wheel carriers (also not galvanised) shows what a nasty environment that area is for exposed steel. The thinner the steel section the faster it rusts away. Citroen used thinner steel plate on the Mk2 carriers which is why most are far worse. The rear subframe and the carrier sit in a large recess under the car. One of the few parts of an XM body that are not fully air smoothed. This will generate low pressure and eddy currents trapping a proporting of the air stream with all its muck, salt and water encouraging condensation on all the exposed steel. The XM Estate sufferes even worse just because the recess is quite a bit larger. The thinner steel components are most at risk in this environment so it is the thin pipe work on top of the main tube and the thinner plates at the lower back end of the rear subframe that really can get hit by rust.
If the car was always put into a dry warm ventilated garage any water dried off quickly preventing the rust process getting underway. If it reqularly sat outside it was probably damp underneath and gently running the rust process for at least half the year. These are extreams but I estimate that my outside car will have suffered about 20 times the rust damage that the garaged on will.
John