- Jan 26, 2001
- Asheville, NC
- 1973 converted to 1980 custom convertible
New problem has happened and can't figure it out. If I start car and let it idle it shows approx. 180 degrees on mechanical temp gauge and dash gauge. Then after warm up but still idle, gauges jump up to around 220-240 degrees and then quickly drop back down to 180. If I drive car over 35 mhp the temp jumps to around 220-240 degrees. As soon as I drop speed, temp drops to around 210 degrees and when I stop car it idles at around 180 degrees again. I have had the radiator flushed and rodded, new coolant, new fan clutch, two new 180 degree thermostats, new radiator hoses, had radiator cap pressure checked, installed seals around radiator, checked water pump impellers and bearings which looked great. The problem seems to be opposite what it should be. The car should idle warmer then driving 35 mhp I would think. The only thing I have not worked on is the block itself. Could it be some blockage in the block? I can see circulation in the radiator and feel flow through upper radiator hose. The strange thing is that the temp jumps up within about 1 minute or less from 180 to over 220 degrees when driving. Then it cools back down within a minute or two. If it were a real overheating problem, I would think the temp would take longer to rise and fall as coolant does not heat and cool that fast. Both the local auto repair shop and my local parts guy suggest it sounds more like air in the cooling system. If so, how do I get the air out? I even drilled a small hole in the thermostat to let air purge better. When I last filled the radiator, I jacked the front up to get the radiator higher than the engine to reduce possible air into the system. I had the parts guy use his infared temp gauge today which never showed more than 200 degrees. How can I have two temp gauges installed on the car showing an overheat while the infared temp gauge does not. Furthermore, what would cause the temp gauges to jump around like that. Any thoughts or suggestions? Anyone else have a similar story?