Temp Gauge/Temp Question

[M3xpress]

So my B2 has a Sun Pro Temp gauge that I go by instead of the stock gauge in the truck (doesn't work). The truck has been running around 180 on the interstate at night, a little bit more in the day time and in traffic.

Today when I was on the interstate the needle went to 250 and then the needle would move back and forth a few degrees.

I pulled the truck off the interstate, popped the hood, and there was no steam, no coolant anywhere, leaks, etc. and the radiator cap was cool to the touch.

As I would take the truck out of gear and slow down the needle would drop from 250 to 210. The truck did not run any different this morning during all this.

The water pump and thermostat have been replaced in the truck, and the truck has already had the head gaskets and heads replaced from the truck running warm before.

I was going to have my radiator boiled for blockage at the end of the summer bc it was running a littler warmer on the interstate than on the street, but it still was running under 200 degrees. Once we got out of the extreme heat, the truck stayed real cool.

Am I looking at a gauge/sending unit issue or an actual cooling issue? I would have thought that if the truck was running that hot, it would be running like crap, missing, steaming, and boiling over.

 

[xr75er]

I'd check to see if the coolant level is correct. an air bubble can cause this.

 

[M3xpress]

I checked the level, it was a little low, but not surprisingly low. I added some water to get the level back up and let it run for about 10 mins.

The truck idle'd at a smidge above 180 degrees. I will have to see how it does when I leave work.

 

[M3xpress]

After letting the truck run without the cap for a bit, and toppin' it back off. I think it was an air pocket, the truck has been running around 180 degrees since.