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Need some help with an older truck

Discussion in 'Car Forum' started by MyGlockRocks19, Feb 25, 2008.

  1. MyGlockRocks19

    MyGlockRocks19 Thread Killer

    I've got a '79 Chevy C-10 pickup with a 305 under the hood, and every time I put a thermostat in it, it overheats. I've tried 3 or 4 thermostats, and I know I'm putting them in the right way, but it'll run for a few minutes, get hot, and stay hot. Eventually it'll overheat and stay there until I shut the engine off, then it cools down and will run cool for a while until it gets hot again. It seems to mostly do it at speeds over 30 mph, and the upper radiator hose collapses when I hit the gas.

    I've tried flushing the cooling system to no effect, and have tried numerous thermostats. Without a thermostat it runs cold as hell. I'd leave it alone, but without a thermostat it runs like crap and burns a lot more gas. I'm pretty sure its not the headgasket as my oil and coolant look fine, and I've got no smoke coming out of the tailpipe.
  2. Sounds like a cracked head. Maybe the crack only opens up when the temp gets high enough. Leave the cap off and let it warm up and watch to see if the water foams and bubbles. Or leave the cap on if it's goosd shape and watch what happens to the water in the overflow.

  3. tried a higher temp thermo? like a race-grade style?
  4. Clem Eastwood

    Clem Eastwood

    Mar 7, 2004
    DFW, TX
    does it loose coolant? if not its unlikely its a blown head gasket or cracked head. 305s are notorious for running hot when in perfect running order, so that doesnt help things. anyway, how old is the radiator? it could just need to be cleaned out or replaced. getting hot at higher speeds is a symptom of this. also, put another upper radiator hose on it or put a spring inside the radiator hose where its collapsing. you need to do this before it can truely be diagnosed.

    if the radiator and hose dont work, and since you dont like how it runs w/o a t-stat; try running a restrictor instead of a thermostat. it doesnt flow as much as no t-stat but still flows constantly. you can get restrictors from summit racing or jegs, maybe even your local parts store.
  5. You can make a restrictor with old thermostat. Just cut the cone out of the top and remove the center section.