Converting big, thirsty vehicles like the F100 to run on LPG was a pretty common thing a few years ago. Then the pump prices of LPG and petrol become close enough that there wasn’t really the cost advantage to be had with an LPG conversion. Couple that with the cessation of local car production (which also spawned a few factory LPG cars) and suddenly, LPG had disappeared into the shadows a little.

It shouldn’t have, as LPG is plentiful in Australia and could have been our alternative to diesel had the industry been developed correctly, the advantages marketed properly and the Federal Government taken a less than greedy view of selling the stuff overseas cheaply while taxing it heavily here. Meantime, anybody who bought a diesel instead for the running costs must be looing at diesel prices now and be wondering if they made the right call.

Anyway, the vast majority of these LPG conversions were to what’s called dual fuel. That is, the vehicle can run on LPG or, at the flick of a switch, on normal unleaded. But some cars were converted to be dedicated LPG runners and couldn’t use ULP at all, which I’m assuming is what you have.

This makes the car less attractive to some buyers, but as fuel prices creep upwards, maybe the allure of LPG will make a comeback. Certainly a big, heavy truck like an F100 has more to gain by running on LPG than a smaller, lighter vehicle.

It is possible to convert the F100 back to run on petrol, but you’ll need to find all the original fuel system components including a tank, fuel pump, lines, filters and the appropriate carburettor. Then you need to decide whether to leave the LPG tank in place and convert to a dual fuel set-up, or ditch the LPG altogether for ULP-only running. Either way, you could be up for a couple of thousand dollars or more by the time you’re done. Which then begs the question whether that will then add the same amount to the vehicle’s asking price.

These older Ford pick-ups are actually quite collectible now with a big following that is prepared to pay big money for the right example. The main factor in value these days is the overall condition of the F100. Specifically the body and whether it's rusty or not. Rust was the big killer of these vehicles which were originally designed and built for the throw-away North American domestic market. Throw in the fact that they were first sold as workhorses and you can understand why the ones that have survived are worth money.

The chassis must also be sound if the vehicle is to have a future and the driveline will determine value, too; the bigger the V8 engine, the more collectible the vehicle is.

With all that in mind, you might pay a few hundred dollars for a very rusty, incomplete box of bits, all the way to $60,000 or even more for a restored example in really nice condition. Values in the collector car market are continuing to fall post-Covid, but the arrival of the all-new Ford F-150 won't hurt the values of these old girls one bit.

1800kg does seem low, but it’s before manufacturers began giving their vehicles a towing rating. I suggest you contact your state registration authorities or the RACQ and ask them.