The previous owner that I bought the pickup from never had a thermostat in the vehicle so the temp gauge read cold all the time, even when driving it. I had put in a new thermostat yesterday, drained/flushed old coolant and put new coolant (I made sure there was no air bubble in the system), and when test driving it around the block, I noticed the heat gauge had gone all the way up to H. I parked the car till it was cool, then checked for any air in the cooling system and there doesn't seem to be any.

Anyone has any ideas?

*The truck has a newer radiator and radiator cap already.

 

Its probably air. I had this problem with my 4runner after I replaced the thermostat. Try jacking up the front and squeezing the lower hose where it has that bend while its running

 

Thanks for the quick reply drmix. I will do that now.

 

indeed. Drmix spot on. that sucker probably has a huge air bubble in it. run your heater on full blast, hot side too wile you do it. get that front end as high in the air as you possibly can and message your lower radiator hose like Drmix suggested.

you should be able to notice it burp.