No Heat and erratic temp guage, whats going on?

What's wrong with my truck?

2005 Taco, 4x4

Heater won't blow hot air. AC works fine (blows cold). I'm getting no errors on the dashboard warnings. However, this morning I noticed my Temp gauge was pegged out while in the drive through at Mc Donalds. Once I was up to speed it dropped QUICKLY (15 sec or less) back to normal range. Once I got to work I popped the hood and didn't see/hear anything out of the ordinary.

Any ideas? Thermostat? Water pump?

 

Sounds like you are low on coolant. Did you check to see if the overflow had any coolant in it?

 

Mileage? Last time cooling system was serviced?

Don't let it keep running hot, or you'll be doing head gasket work as well.

 

140k....I'm "pretty" sure I had it serviced before last winter, up until about 6 months ago I was living in Iowa. I'll get it done today after work and see if that fixes the issue.

 

Thermostat

 

2005 truck + air in coolant problem = Head gasket failure is a most likely reason
for problems.
Hopefully its just low coolant level, but since your truck is 2005 and they all seem to have head gasket issue ....