The thermostat is really simple, it is the canister in-line of the radiator hose going to the lower radiator connection. The whole unit is replaced.

The gas line leak could be anywhere, but it is very common for the hoses on top of the gas tank to dry rot and leak gas. You access these hoses by removing the back seat and taking off the two access panels. Some people go so far as to remove the tank for this job, but it can be done without it. Usually the leak is here is it only leaks after you fill it up.

You can use regular 87 octane if you like.
Mike Matison
many e21's
hey all... my friend is going to sell me his 77 320i and i was wondering what kind of milege does this car get and what type of gas is good for 87,89,92

also he said that the gas line is leaking somewhere and has a broken thermostat. are there easy fixes for home or will i have to take it to a repair station.

ok all thanks in advance
rj