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I changed my coolant hoses on my 2001 Ford F150 today. I let it idle for about 15 minutes and then took it for a test drive. It began to run hot during the test drive. What could cause this?

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You have air in your system, which is either causing pump cavitation or hot spots. I took a look around on the internet to see what other sites are saying for bleeding the system (which is what you need to do). I could not find any that suggested there are bleeder screws to clear out the gas pockets, so the next best thing is to have you park the truck pointing uphill and allow the vehicle to cool totally. Pop the radiator cap and top off if needed. Turn your heater temp control selector over to full hot and your direction selector to the floor (for heater - I wouldn't use the defroster during this time). Once topped off, run the vehicle up to operating temperature, keeping a close eye on the temp gauge and continue to top off if needed. Once up to temperature, put the radiator cap back on and take it for about a 10 mile test drive. You want to drive somewhere like on a highway where it will see some decent engine speed for a longer period of time. Keep a close eye on your temp gauge and signs of overheating. This should properly bleed your system, but may take a couple of iterations to get it done.

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ensure bottom hose contains a spring so it doesn't collapse when hot.Replacing thermostat is never a bad idea.If radiator is old replacing or re-coring is an option.Many people have bullbars/winches/driving lights restricting airflow.A thermo fan that you can turn on or off via dash switch is a worthy consideration

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