Collapsing fuel tanks
Page 26
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THE VACUUM created in Mrs Parnaby's Granada fuel tank (See CM October 19, 1979) was almost certainly not caused by the cap being too tight, but by use of the wrong type of cap.
Fuel tanks are of two types, and depending on type they require either a vented or nonvented cap. The use of a nonvented cap on a non-vented tank can cause the tank to collapse, and strongly suspect this is what happened to the other Granada Mrs Parnaby heard of.
For this reason, it is dangerous to transfer petrol caps, particularly locking caps, from one vehicle to another without making sure that they are not only the correct size but also the correct type for the new vehicle.
While drilling a hole of adequate size will no doubt vent a non-vented cap, there is a danger that petrol may leak out, either when the tank is full or in the event of an accident. It may also allow water and dirt into the tank. Normally the venting of a purpose-made cap includes a ball valve to prevent this.
D. C. PETERSON Upper Cornsland, Brentwood, Essex