I have a 1999 Ranger that has been exhibiting weird symptoms lately.

When I first start it up in the morning, it takes a long time to get warm. The temp gauge will take a long time to creep up and then stay just above cold for awhile. At the same time, the heater from the defrost will only blow cold air (even if I have it set for warm air). This is after a long enough time that it used to blow hot air. And then suddenly the gauge spikes up to hot (like over heating) and then settles in to normal operating temp in the middle. And at the same time, the heater starts blowing warm air like normal and everything seems fine.

This isn't the first time that odd heating issues happened before. In the summer, when I was stopped at a light the temp would spike. So I got the coolant flushed and it was all brown and gross and the guy thought there was air in the system. It seemed fine for about the last 6 months but just started again.

Any thoughts?

 

Thermostat most likely

Reverse heater hoses at the firewall as well, should do that every 2 years, reversing flow keeps heater core cleaner to last longer
When heater hoses are off at firewall top up coolant, you could have an air bubble in the engine

To test thermostat, start cold engine
Open the hood
Feel upper rad hose and heater hose at firewall, both will be cold of course
Wait 2 or 3 min
Feel hoses again, upper rad hose should still be stone cold, heater hoses should be warming up
If rad and heater hose feel the same thermostat is open when it should be closed

Radiators are for EXTRA heat, in cold weather they may not even be used, so upper hose will stay cold until there is EXTRA heat, coolant in engine above 190degF, just below 1/2 on a Ford temp gauge

 

Right on, thanks a lot! I'll give it a try this week (probably just replace the thermostat anyways since looks easy and cheap).