GM Truck Club
THE PREMIER CHEVY TRUCK & SUV FORUM
Founded in 2004 ~ We're the #1 Chevy Truck & SUV Forum.
Silverado & Sierra | Tahoe & Yukon | Suburban & Yukon XL | SUV & CROSSOVER
Page 1 of 2 12 LastLast
Results 1 to 10 of 11
  1. #1
    Sr. Apprentice
    Join Date
    Sep 2011
    Location
    Rockwell, North Carolina, United States
    Posts
    53

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

    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.
    BUILT, NOT BOUGHT
    1985 Chevy Silverado Longbed 4WD
    400 Chevy Small Block/400 Chevy Transmission
    Detroit Lockers Front & Rear/4.10 Gears
    35" BF Goodrich Mud Terrains/6" Rough Country Suspension lift

  2. #2

    Default

    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. #3
    Sr. Apprentice
    Join Date
    Sep 2011
    Location
    Rockwell, North Carolina, United States
    Posts
    53

    Default

    Quote Originally Posted by Chris Miller View Post
    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.
    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.
    BUILT, NOT BOUGHT
    1985 Chevy Silverado Longbed 4WD
    400 Chevy Small Block/400 Chevy Transmission
    Detroit Lockers Front & Rear/4.10 Gears
    35" BF Goodrich Mud Terrains/6" Rough Country Suspension lift

  4. #4
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    487

    Default

    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.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  5. #5
    Sr. Apprentice
    Join Date
    Sep 2011
    Location
    Rockwell, North Carolina, United States
    Posts
    53

    Default

    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. #6
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    487

    Default

    OK, I got nothing.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  7. #7
    Sr. Apprentice
    Join Date
    Sep 2011
    Location
    Rockwell, North Carolina, United States
    Posts
    53

    Default

    No prob man, it's prob a combination of things trying to work them out now.

  8. #8
    Sr. Apprentice
    Join Date
    Sep 2011
    Location
    Rockwell, North Carolina, United States
    Posts
    53

    Default

    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.)
    BUILT, NOT BOUGHT
    1985 Chevy Silverado Longbed 4WD
    400 Chevy Small Block/400 Chevy Transmission
    Detroit Lockers Front & Rear/4.10 Gears
    35" BF Goodrich Mud Terrains/6" Rough Country Suspension lift

  9. #9
    Sr. Engineer
    Join Date
    Oct 2010
    Location
    Indianapolis, In
    Posts
    487

    Default

    Thanks for the update. Always seem to be a bug or two to work out on fresh work. Good luck with the electrics.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  10. #10
    Sr. Apprentice
    Join Date
    Sep 2011
    Location
    Rockwell, North Carolina, United States
    Posts
    53

    Default

    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 by Royce Lancaster; 07-04-2012 at 10:35 PM.
    BUILT, NOT BOUGHT
    1985 Chevy Silverado Longbed 4WD
    400 Chevy Small Block/400 Chevy Transmission
    Detroit Lockers Front & Rear/4.10 Gears
    35" BF Goodrich Mud Terrains/6" Rough Country Suspension lift

Page 1 of 2 12 LastLast

Similar Threads

  1. Chevrolet : Other Pickups CHEVY LUV TRUCK V-8 SMALL BLOCK CHEVY
    By Steve in forum Chevy Trucks For Sale eBay
    Replies: 0
    Last Post: 01-10-2011, 09:40 AM
  2. Chevrolet : Other Pickups CHEVY LUV TRUCK V-8 SMALL BLOCK CHEVY
    By Steve in forum Chevy Trucks For Sale eBay
    Replies: 0
    Last Post: 01-02-2011, 03:40 PM
  3. 77 chevy 400 small block vaccuum diagram?
    By socal77k5 in forum GM Powertrain
    Replies: 1
    Last Post: 06-08-2010, 03:10 PM
  4. World's Smallest Chevy Small Block!
    By retired2001 in forum The Coffee Shop ~ Chit Chat
    Replies: 16
    Last Post: 06-08-2009, 01:13 PM
  5. What's running Temp. for a Small Block Chevy 69?
    By Holy Smoke in forum GM Powertrain
    Replies: 0
    Last Post: 01-09-2008, 03:47 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •