Full resivor Coolant low temp fluctuation
I recently started having trouble with my Ford ranger. I developed a small pin hole in the pipe running to my Intake manifold I patched it, and refilled the coolant. now my tempauature gage fluctuates about 10 minutes into the driveit will drop down to cold, then go up to hot, then drop to normal. then occasionally it will intermittentaly fluctuate from normal to half way to red then drops back down to normal.
Today while driving it heated up and stayed at the 3/4 mark so I let the truck cool for about 30 minutes, I then checked to resivor. it was almost completely full. I opened the radiator cap, and it was almost a gallon low on coolant.I refilled it, and it ran for about 20 minutes at normal.
I had it pressure checked 2 times 4 days ago, and it hold pressure steady. Can anyone give me any help? my mechanic cant find the problem.
Thank you much.