About six weeks ago I had over hearing issues, I did a flush and replaced the thermostat and had no more problems... Until this morning, I was running a high temp on my way to work, on my way home I over heated. Got home did another flush and put new coolant in. It over heated again. Turned it off, let it sit for a bit. Now it's running fine at a normal temp. What could cause this?

 

Bad fan clutch is common. Could have air in the system if yours is a closed system. A bad water pump could be the case too. You have a lot of places to look, a flush and tstat is a decent start though.

 

Pay attention to WHEN the temperature starts to rise. A simple "it overheated" isn't going to help you diagnostically. (Unless you have the idiot lights, in which case that's really all you've got)

If the cooling system is old chances are everything needs replacing, but let's find out what's happening first.

Up hills? At stop lights? While in motion? Just how hot are we talking about? Blowing steam or a warning light? Or 220 on the gauge?

Did coolant come out when you flushed it or old sludgey water?

 

I just did the clutch fan test and that's still good, just for more info. Thermostat should be good, only a month old. It was over heating anywhere/everywhere. It was blowing steam and coolant out. I did a good and it was somewhat sludgey but not to gross. After I flushed it and added new coolant I let it get up to running temp and let it run and temp kept climbing until I turned it off when it started spitting coolant again. I let it sit for a bit then started her back up and it's running fine at normal temps.

More info is that I replaced the thermostat 6 weeks ago after having over heating issues and haven't had a problem til today.

But like I said its running fine now. My main concern is will it continue to run good or is something slowly going bad? Maybe something is making the system to get clogged up?

Hope that gives you enough info..
Thanks.

 

What sort of thermostat did you use? Did you replace the cap?

 

When you flushed system was coolant nasty coming out .I recently did mine and had very similar issue this is what I found .Now all my coolant items fans,stat,pump and hoses are in great working condition. Flush loosened this out of heater core. Causing particles to plug coolant passages when cruising then they would fall back to bottom when stopped. This is just one possibility mind you.

 

The caps on those bottles are generally chinese junk and the threads on the bottle marginal. Replace the cap with a 703-1396 from Napa as a next step.