Plastic tanks have been around for a long time now, Ford Australia first started mucking about with them in the late 70's and Ford US were using them in the mid 70's.
The phenomemon of them expanding once fuel was put in them was known about over 20 years before MG-Rover started using them. and there have been no other ill effects from this expansion other than making the tank difficult to remover from a confined space. Something that some idiot at MG-Rover overlooked when designing the tank!
Plastic tanks are fine so long as they're properly designed and constructed, indeed they offer some advantages such as light weight, rust free, good impact resistance, cost etc.
There are some disadvantages too, but these should be accounted for in both the design and manufacturing processes, obviously the expansion can be a problem as can the problem of some owners complaints of fuel smell in the car, this I believe is due to a lack of a critical additive in the molding of the tank.

Read More...