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Over heating problem

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by chev4life, Aug 30, 2004.

  1. chev4life

    chev4life 1/2 ton status

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    Well, it has been like this for awhile and I need some help. My '87 K5 seems to get real hot...not meltdown hot, but hotter than I like during driving in hot weather or up big hills...210 up to 220 or so. I have replaced the radiator already, the T-stat was replaced about a year ago. Anything I shoudl look at? It has the stock fan (132k on stock motor), the water pump was replaced about 5 years ago, but isnt leaking at all that I can tell. But my overflow seems to empty alot and it was dumping good this weekend after a hard drive in high heat. What should i look at???
     
  2. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    How well does the A/C work? If you are getting poor A/C performance from a system in good shape at low speeds than I would suspect you are not pulling enough air to keep everything cool. Check the clutch for any signs of oil leakage. ALso make sure that the tbi isn't leaned out for some reason. Are you shure your gage is correct also? Mine was off a few degrees when I was having temp problems.
     
  3. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    How well does the A/C work? If you are getting poor A/C performance from a system in good shape at low speeds than I would suspect you are not pulling enough air to keep everything cool. Check the clutch for any signs of oil leakage. ALso make sure that the tbi isn't leaned out for some reason. Are you shure your gage is correct also? Mine was off a few degrees when I was having temp problems.
     
  4. chev4life

    chev4life 1/2 ton status

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    Yeah, the temp guage is something I thought about, but the overflow dumping from the heat makes it seem like it is reading somewhat correct. The AC blows great at all speeds, that also caused the temps to go up a bit more. Do you use a stock style, clutch driven fan? I am thinking that I shoudl replace that.
     
  5. Blue85

    Blue85 Troll Premium Member

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    Have you checked the fan clutch?

    The A/C working well suggests that it is working, but it's the only simple thing you haven't looked at yet.

    If the engine is stock the stock hardware should be sufficient to keep it cool. What temp thermostat are you running? Are you sure there is no air trapped?
     
  6. chev4life

    chev4life 1/2 ton status

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    Air trapped? How do I check the fan clutch? I figure I should have plenty of cooling. I am sure the 35" ssr's dont help, but my gearing is slightly shorter than stock when combined with the tires so the RPM's are good on the highway.
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    In normal "light load" driving it heats up, or is it when the vehicle is idling, like in traffic?

    Very important whether it happens while the vehicle is moving or while it is sitting.

    If you suspect the fan clutch, and it heats up while moving, but not idling, I'd pull the fan off and take it for a spin on a road where you won't have to put a big load on the engine, but can keep it going 35MPH or more constantly.

    I know it sounds counter-intuitive, but failed fan clutches HAVE been known to cause overheating while moving.
     
  8. chev4life

    chev4life 1/2 ton status

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    Hmm...it has never given me any problems at idle...stay cool, and sometime cools down at idle, stoplight/etc...It seems to only happen when driving/driving hard (pretty much the same thing /forums/images/graemlins/grin.gif) I will check the fan clutch..is there a tell-tell sign that it is bad?..ok?
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    If it's while driving, pull the fan off. That's how I'd check it. Obviously it's working at idle, but it still might have failed...pretty hard to tell if it is staying locked up.

    It is about the only item you can fairly easily test in the system. If you pull it off and the problem is gone, you've found the problem. If it doesn't, you've eliminated one potential problem.

    Don't expect to drive it anywhere important without the fan. Sitting at idle, it WILL overheat rather rapidly with no fan.
     
  10. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    [ QUOTE ]
    Do you use a stock style, clutch driven fan? I am thinking that I shoudl replace that.

    [/ QUOTE ]I have dual 13.5" electric fans because my mechanical couldn't pull enough with a hacked fan shroud from the body lift. For you the stock setup in working condition should keep it perfectly cool as long as the engine itself is basically stock.
     
  11. chev4life

    chev4life 1/2 ton status

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    I have thought about getting the dual elec fan setup, but just havent felt it was necessary. The single should be fine. The truck is stock except for exhaust and soon to be headers. I am going to start with the fan clutch and replace the tstat fro good measure when I do my tune up. THanks for the help guys, I will keep you posted.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    I personally would NOT mess with the t-stat right off the bat.

    I know they are "cheap", but you've still got to make a mess to get it out.

    My reasoning is that the problem isn't consistent...regardless of whether idling or cruising, the t-stat should act the same. If it was stuck open, you would notice lower temperatures than normal, especially at cruise. If it were stuck closed, idle would quickly overheat the engine.

    Now I'm not going to argue the "too much flow" theory with anyone, since the thermostat is still in place, and even if stuck wide open, is still a restriction.

    It could be the thermostat, since pressure on it is going to vary, but it seems HIGHLY unlikely that is the issue.

    Is your radiator cap holding pressure?

    Just my thoughts and observations from over the years.
     
  13. jwduke

    jwduke 1/2 ton status

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    Sounds like your clutch fan is slipping at higher speeds. Thats what the one on my '87 did, till I replaced it.
     
  14. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    There is one way of testing the fan clutch, but it is dangerous if not done right. /forums/images/graemlins/smile.gif

    Take a very thick glove( like a welding glove)and with the truck idling set the palm of your hand on the top of the shroud and just slightly (slightly!!)touch the fan with your fingers. If the fan clutch is slipping the fan will stop when you put your fingers on it. If it's good....I don't know what will happen, mine was bad. /forums/images/graemlins/dunno.gif /forums/images/graemlins/histerical.gif Anyway this is how our local rad, alt., starter rebuilder guy tested mine.
     
  15. chev4life

    chev4life 1/2 ton status

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    Yeah, I have heard of that way, just havent sucked it up to try it...just not a safe idea. Maybe a tough piece of cardboard could do it.
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Since the fan is ESSENTIALLY on or off, you'd have to make sure the fan was SUPPOSED to be locked up when you tested it.

    Anyone happen to have a GM service manual that can tell us what the actual test is for the fan clutch?
     
  17. dmanblazer

    dmanblazer 1/2 ton status

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    Symptoms of clutch fan failure are continuous noisy operation, loosness leading to vibration and evidence of silicone fluid leaks. If you can grab the fan and give it a shake and it moves up or down side to side or back and forth then you probably have a problem.
    Other problems could be not enough coolant, belt slipping or not adjusted right have someone working the throttle while you listen for a squawling noise and watch for belt flex, radiator core blocked or cooling fins dirty try flushing it, thermostat bad, broken or cracked fan blades, radiator cap not holding the proper pressure have it pressure tested check for dents in the mouth of your sealing surface or any out of roundness, timing not right, air in the system you can belch the cooling system buy drilling a some what very small hole in the flat part of the thermostst or pop a heater hose off the engine while filling the system.
     

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