Re: heat only after 10 min. and driving down the road
Yep, here's one.. If you follow the heater hoses back from the where they enter the firewall, towards the radiator, you'll find a little valve inline with one of the hoses. It is vacuum controlled and it's possible the diaphram is leaking or the vacuum hose is rotting away/collapsed. Had this happen to mine with the same symptoms. Replaced the diaphram and worked as it should for about a week, then the heater core started leaking... but that's another story.... Never another problem with the diaphram though.
1996 Mazda B2300 SE
5 Speed Stick
(Well it's almost a Ranger!)