Hi, I have a F150 with a 351 speed auto on gas and petrol.
I have just repaired a broken radiator mounting bracket (removed, repaird and refitted radiator) and replaced the thermostat, 81 c to 91 c (engine running tooo cold,needle never moved of cold).
When I had finished, I started engine and ran for 10 to 15 minutes, engine temp moved up to the middle of the nornal range, no coolant leaks, so all good, turned engine off.
30 minutes later tried to start engine, nothing no start no nothing just turning over on starter.
MMM i thought, maybe I had flooded it when trying to start. So I waited 30 minutes and tried again, nothing,turns over really well but no firing up,
What could the problem be ????

Got fuel and spark?

I'd say check plugs and leads and cables. might have accidently pulled something removing/installing
Radiator

it ran really well after I had finished with radiator. Now nothing, turns over on starter but no firing up.

Once again...Have you got fuel and spark?

Today I decided too check fuel and spark as suggested. Had a check under bonnet and could not see anything out of place. Turned ignition on and tried to start, took a bit but eventually started. Let it warm up and turned engine off. Waited a few minutes and tried again, no problems started straight away . Waited 3/4 hr and just tried again, no problems,
Grrrr I can see why cars are referred to as "she", so bloody temperamental.
I must have flooded it ,it is the only thing I can think off.
Thanks for your help.