06 Explorer 4.6L Temperature Gauge fluctuating at speed

[bpd9]

Hello everyone, just got myself an explorer, new to the forum! So a few weeks in, the first morning it was cool out enough to turn my heater on, the temperature gauge started jumping. Now a few days later is continues to jump at at speed. It will raise up from right about halfway to the 3/4 mark, never making it all the way to red, then will suddenly drop back down a bit and kind of move around from there. Then when I slow down or drive under say 20mph the temp gauge goes right to where it should be. From past experience with other cars this tells me there has to be air in the system somewhere. Especially since the heater kicked on for the first time since I've owned it and that's when the problem started. Only now it happens regardless of outside temperature or whether I have AC on or heater or anything. I've tried burping/bleeding the air out to no avail. I had it running for a good 30 minutes with the front end jacked up and heater blasting. Think I should just try to flush the system out and fill it from empty to make sure there is no air? I'll check the tstat at that time as well, but is there anything I'm missing or any suggestions? Thanks all!

 

[Explorer_PL]

I do not that problem but after I replaced a radiator, I had air in the system for a while and I drive a lot - sometimes 100 miles a day. I had to add fluid few times until it stopped dropping. I almost thought I am loosing it somewhere.

 

[Flag Gibby]

Sounds like the Tstat could be starting to fail or the temperature sending unit could be acting up particularly if the Tstat is not the OEM design that fails open. No need to flush the system to check the Tstat since it can be pulled from the housing without losing a lot of coolant.
Edit: I should clarify, you can check what manufacturer Tstat is in the vehicle without losing a lot of coolant, but if you pull it out you will lose a decent amount of it unless you seal the top hose so that it creates a vacuum on the system and it cannot flow out easy.

 

[bpd9]

Good point, and the coolant looks pretty clean. I bought it from a dealership so I'm wondering if they replaced the coolant and just did a poor job and didn't open up the heater core so push the air out. I'll check the tstat tomorrow morning and throw it in a pot to see what temp it opens up at. Might as well not waste all that coolant. I'll post what I find out manana. Thanks

 

[Flag Gibby]

bpd9, see my update above. At this point I have a hard time thinking that there is air in the system since the last time I changed out my Tstat it didn't have any air circulating in it after the 15 minutes that I ran the engine for with the heater on full blast in order to "burp" all the air out and I lost about half of the coolant out of the system when I changed the Tstat because I was not paying attention to what I was doing at the time.