To address the OP, I have recently had somewhat similar troubles, minus the bubbles in the overflow tank. It was suggested I do HGs, but for the lack of money, I decided to try a flush + new rad cap for the time being. That stopped the car from overheating, but temperature started to fluctuate, getting hotter at idle or low speed after driving highway speed for some distance, then back to normal once I speed up. Long story short, I traced it to a broken bleeder screw in the radiator. I think the guy that did my timing belt in the summer, broke it, and then just jammed a screwdriver in the what was left of it and screwed it in. Must've not noticed the gasket in the there. Once it got cold, it must've loosened up a bit and let air in and coolant out. I replaced it with a regular hex bolt of matching thread/size (m10-1.25), and no problems for the past three days. Hope it stays this way for a couple years.

To address the OP, I have recently had somewhat similar troubles, minus the bubbles in the overflow tank. It was suggested I do HGs, but for the lack of money, I decided to try a flush + new rad cap for the time being. That stopped the car from overheating, but temperature started to fluctuate, getting hotter at idle or low speed after driving highway speed for some distance, then back to normal once I speed up. Long story short, I traced it to a broken bleeder screw in the radiator. I think the guy that did my timing belt in the summer, broke it, and then just jammed a screwdriver in the what was left of it and screwed it in. Must've not noticed the gasket in the there. Once it got cold, it must've loosened up a bit and let air in and coolant out. I replaced it with a regular hex bolt of matching thread/size (m10-1.25), and no problems for the past three days. Hope it stays this way for a couple years.

 

Good catch! That is actually one of the things that a pressure leak down test would catch. I had an overheating issue two years ago that I was certain was due to bad headgaskets. I checked the radiator for hydrocarbons but there were none. I also checked it for bubbles and there were plenty. I was constantly having to add more coolant (about a gallon a day). I finally rented a leak down tester from AutoZone and pressurized the radiator to 16 PSI. Immediately I heard a hissing noise and the pressure was dropping quickly. I wiggled the upper and lower radiator hoses and found that the upper hose had a leak in it. When I wiggled the upper hose the hissing noise also wiggled. I replaced the hose, used new clamps and retested. No more hissing, no more leaking, no more overheating.

Sorry late to the party.. It's the Head Gaskets.

 

 

Mine did it back in April as the video lists.. I finally changed them in Aug. Been fine ever since then

 

if it's not already been said it's how the sender for the gauge is because of no coolant running over the sensor to cool it down then When the piston is not pressuring the radiator it starts flowing normal again.

 

I took many pictures of the old gaskets never made it to the oil passages (thankfully) About 3,000 Mi on the new gaskets.

Edited November 6, 201114 yr by 1-3-2-4