Okay, so this is the first time I've had an issue with my truck running hot...in 5* weather, go figure...

So I started up the truck this afternoon, drove to the store down the street. Let it idle while I ran in so it could warm up. I came back out, temp gauge had barely moved, so I decided to drive around for a little bit so it could warm up. Finally the temp gauge moved towards the middle, but the heater still is blowing cold air. Thought it was a little strange, but kept on driving for a while. Finally the needle moves up into the upper range and into the red so I pulled over and shut the engine off. Still blowing cold air, mind you.

I popped the hood, backed the coolant reservoir cap off a few notches at a time as I let the engine cool. Finally got a normal temp indication from the gauge, so I fired it up and started to drive home. Heater blew hot air all the way home and temp stayed in the normal range.

So my question is, what gives? The truck doesn't leak coolant, and it seems to be a one-time problem. My one theory is that the shady-*** dealer I bought it from (in August) may have filled the radiator with water instead of a 50/50 coolant mix. Would this cause the problem I described? Is a drain/flush and refill my first step towards resolving this issue?

 

Could have been your thermostat locked up. My truck did this same thing when I blew a head gasket. Acted like a really small problem but finally a miss code came up. But most likely sounds like the thermostat isnt opening. If it does it again, get out and grab the hose going to it... if it is solid as a rock, its not open and has a ton of pressure. If you can squeeze it its open. Wont hurt to do a coolant flush. Easiest way is to by one of those tools for a few dollars and check the temp your anti freeze is good to. If its water(maybe even a 50/50 mix in 5 degrees) you might start having major problems!! Also one thing I've learn from my head gasket problem. Ford has redesigned our thermostats 4 times since our generation was built. So even if its a little pricer, go to a Ford dealer. I got mine from advanced, auto zone, and napa before I contacted Ford about the problem... come to find out it the blown head gasket was air locking my t-stat, not the t-stat failing. but good info to know you might get a faulty one if you dont go with the most current. good luck

 

Okay, I'll definitely try a flush & refill this weekend, and try the t-stat if it happens again...should be relatively cheap and easy, right?

Took the truck out today BTW and lo and behold...no problems at all. It was about 30* outside though, but the heater started blowing hot air when the temp gauge started to move off of cold a little bit. Temp held steady.

 

To rule out a head gasket or worse, grab a test kit from Napa

use a block tester, also known as a combustion leak tester, to determine if you have exhaust gases in your cooling system

 

UPDATE: Problem solved (knock on wood)!

Well the problem came to a head this weekend...heater was acting up all day Friday and when I finally popped the hood to check, coolant was all over the engine bay. Finally noticed my waterpump had a ton of play in it.

So...put on a new waterpump, thermostat, fan clutch, and flushed/filled the coolant (which looked like muddy water and was nearly gone) and it seems to be good now.

Had it in the dealer last week and they did a full engine diagnostic, so it shouldn't have a head gasket issue (when it did overheat I shut it off immediately). Seems like I'm finally starting to catch up on the maintenance that the PO didn't bother to do.

 

literally