My buddy got a 2003 f150 fx4 with 5.4 triton..200 k miles... he got gas then crank up but died..then wait 5-10 minutes then crank back up and run fine..problem happens when key is turned off..the cooling fan comes on..but goes off when key is on acc or on position...he has to disconnect the battery when not in use..any suggestions on cause? Thanks in advance

 

Must be a aftermarket electric fan . Usually you add a fan controller it should be measuring water temp and /or anytime ac system is running it turns on fans . I studied adding electric fans but you need two fans and two controllers plus heavy duty alternator . Very expensive to prevent blowing a head gasket for cooling failure
I will wait for a truck that is designed for electric fans .
Sounds like this one is misapplied and it is running battery down . Controller should run fans when truck shutoff until water temp is reasonable . These fans draw very heavy amperage and need heavy wiring .
usually the fans stay on anytime ac clutch is energized . If alternator not heavy enough the battery will get depleted even while running .
A 12vdc fan needs 10 times the amount of amps as a 120vac fan . So to get 120watts of cooling fan it will take 20 amps of dc or more . 2 fans 40amp , that's a lot of extra load for a standard alternator . Each fan should have no 10 wire to be rated 20amp continuous .
I am not going to add 1000 bucks in new electric stuff and risk blowing a head gasket . I am in a hot climate so that makes it worse .

 

Until I knew what was going on with the fan, controller, etc ... I think I'd look at a stock fan as an option. A single electric fan is gonna be hard pressed to do the job unless it's a high amp large fan. An original fan might have an electric clutch, but the engine actually turns the fan ... at l;east on my '07. Other cars / trucks had thermostatic fan clutches, or like my '77 ... a plain old school large flex fan. Maybe he can use the electric fan as an auxiliary fan, ... I did that on a '85 T-bird to flip on with a switch while sitting in bumper-to-bumper race traffic.

 

My bad guys..sorry info was wonky..his blower fan inside the cab comes on when key is off..and goes off when key is activated..i do appreciate the replies

 

Maybe he has EATC and the blower speed controller is defective. Try disconnecting the blower speed controller and see if it still behaves this way. Also a common issue was water in the fusebox and gem module from a windshield leak. That can cause many malfunctions including blower running with key off

 

i will let him check as you said..it only happened after a significant rain..so makes sense..appreciate the input

 

If that is the case tell him to fix the windshield leak pronto. Those fuse boxes can get permanently corroded up and they are hard to find today.