Chevy 400 small block acting up when hot(1985 chevy k20)?

Discussion in 'GM Powertrain' started by Royce Lancaster, Jul 1, 2012.

  1. So I've noticed in the passed few days since is been hot my truck wants to surge when accelerating and sometimes it acts like it doesn't want to change to 3rd gear. Ive inspected all the vacuum lines, and fuel filter. Trans fluid is fine, oil is slightly low. also the engine is running at about 200˚f when it normally runs at 190˚f, so I'm gonna check all the vacuum lines thoroughly and replace one and if i still don't find anything wrong my dad suggested changing the thermostat from 190 to a 160 and putting new coolant in it, since its running hotter than normal.

    Any ideas whats wrong?
    also The motor bogs down when it doesn't want to change gears, but once it changes its fine. theres no pattern to any of these symptoms so far only when its hot out side or the motor temp has increased.
  2. Chris Miller

    Chris Miller Rockstar 100 Posts

    You might try flushing out the transmission cooler in the radiator. If it's clogged, and the fluid is getting really hot, that can raise your operating temps a bit, and make it look like your engine's running too hot.
  3. I didn't think about this, I will be sure to check it out, seems like a easy fix since I have a after market cooler for the transmission.
  4. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    I would not change thermostat temperature, maybe replace it but not change temp. . If it is working properly and still not able to maintane temperature then the problem lies elswhere. Pumps go bad, radiators clog up internaly as well as externally, to much anti-freeze concentration will inhibit heat transfer, fan cluthes stop working, electric fans stop for a number of reasons and on and on. My 2000 yukon 5.3 runs at 205 to 210 on a regular basis and the manual says that is normal and can go as high as 250 without issue. As stated earlier check trans. cooler and by all means correct the fluid level.
  5. This truck only has 1500 miles on it since I restored it, new water pump, new fuel pump new radiator, new clutch fan, drivetrain wise everything is newly rebuilt.
  6. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    OK, I got nothing.
  7. No prob man, it's prob a combination of things trying to work them out now.
  8. I changed the plugs, had one arching on the header, so I fixed that problem, changed the thermostat and anti-freeze, the truck runs great now and stays at 170˚f with the AC on, drove it 200 miles today none stop, no problems. Only the alternator started acting up, no idea whats wrong with it, gonna try to wait it out until I get back home so I can deal with my parts dealer and not the ones at the beach.(It seems to be kicking on and off, I'm gonna have a look at the wiring when i get a chance, it may be my voltmeter because the battery doesn't seem to be getting weak at all.)
  9. dpeter

    dpeter Epic Member 5+ Years 500 Posts

    Thanks for the update. Always seem to be a bug or two to work out on fresh work. Good luck with the electrics.
  10. Alternator bolt was sheared off in the head, spend a few hours trying to get it out. I still think the regulator is bad.
    Last edited: Jul 4, 2012

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