I'm once again hoping the TBN/CBN team comes through.

I have an '89 Chevy truck that was recently in for some work (previous post "Chevy front end work"). While it was in the shop, I had them flush the radiator and replace the thermostat (the temp gauge would occasional spike and then drop back to normal so I figured the t'stat was sticking now and then).

I got the truck back and the same thing still was happening, only it got worse very quickly. The gauge will now slowly rise and stay pegged (I obviously turn the truck off when this happens). I changed the thermostat and water pump and I still have the problem. I even pulled the thermostat out and I still have the problem. I replaced the engine coolant temperature sensor, temperature sending switch and checked the integrity of the wires to both. I still have the problem.

When the gauge is pegged, the hoses to/from the radiator don't get hard, like they would if I was boiling over and there's minimal pressure at the radiator cap when I pull it off (Coolant tests at 260F boiling point, gauge pegs at 250F.) If I turn the heater on, it's warm, but not blazing. The upper radiator hose isn't hot along it's length (like if the t'stat was closed). Also, if I crimp the upper hose, it doesn't feel like I've stopped any flow.

I'm now puzzled and think it's one of two things. 1. the gauge cluster or 2. that the radiator is plugged.

I'm thinking the radiator is plugged. I would have thought the repair shop would have told me something wasn't right when they flushed the system (I wasn't there to witness the work so I can't say for sure that it was flushed) A plugged radiator would prevent, or reduce the amount of coolant actually being pumped and would lead to the cold upper hose and lukewarm cab heat (I think).

Does this sound plausible? Any surefire way to check for a plugged radiator?. Can I pull the upper hose and see how much volume flows out while it's running with the t'stat out?

Any and all help appreciated.