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  1. #1
    Join Date
    Jul 2007
    San Jose, California

    Default 1987 GMC Suburban runs hot while towing

    Hi All,

    New user here... I have an 87 Burb with a 350 and when I tow my boat, it runs hot. I put a bigger radiator and a cooler thermostat, but it still runs warm and very hot going up a hill (have to turn on the heater to keep it from overheating).

    When I look at the front of my Burb, I have the tow running/blinker lights, the air conditioning and transmission coolers in front of my radiator. So, not much air is really hitting the radiator. A thought that I had was to move the transmission cooler and mount it on the fender well with a fan connected to it.

    Has anybody done this successfully? Or, does anyone have a suggestion or two about this?

    I have looked in the forums here and in other places, but have not found anything.

    Thanks in advance.


  2. #2


    Your problem isnt the items in front of the radiator. You need to look at the cooling system itself. Why is it running hot? This combination has been pulling loads for many years without overheating.
    Whens the last time the system was flushed?
    Whats the anti freeze percentage?
    Has the system been pressure checked?
    Has the cap been pressure checked?
    Is the water pump operating correctly?
    Is the Fan operating correctly?
    Is the Transmission shifting correctly, not slipping and creating excess heat?
    Whats the mileage on the engine, is it old and ready for a rebuild?

    Some things to try are:
    Water Wetter. Great stuff, I use it in my rockcrawlers religously, after idling all day long at about 15-20 mph they never overheat. On my tow rig (1996 7.4 Suburban) I saw a 15 deg decrease in temps.
    An electric fan, this will reduce drag on the engine.
    If the engine isnt to old Synthetic oil to reduce friction.

  3. #3


    Ya I would run at least a 50/50 antifreeze or even 75/50 antifreeze mix. The more anti the more it will cool, wait is that right? I forget.

    Or is it the more anti, the higher the boiling point, lower freezing point?

    Flush the entire system yourself at least once.

    Also make sure the clutch fan is working properly, no wobbling. Might even consider a fan with more blades.

    I might even go with a regular fan, no clutch.
    Last edited by 84fiero123; 08-01-2007 at 08:11 AM. Reason: STML i always forget stuff

    Technology is great, when it Works,
    And one Big Pain in the Ass When it Doesn’t.
    Detroit Iron Rules, All the Rest are Just Toys.
    94 GMC Burban, 5.7L (350), 4X4, Auto
    86 GMC Burban, 350, 2 WD, Auto
    79 GMC pickup plow truck, 400, Full time 4X4, Auto
    86 Pontiac Fiero SE, 2.8L, Auto, only mid engine American car
    See a Pattern yet?

    15 year GM assembly line worker.

  4. #4


    your clutch fan might be tired as well for under $60 you can swap in a ford Taruas fan. I just did a write-up on how to do this. my 502 motor home was running in the high range due to a bad electric fan and now it runs mid way and cycles on and off and no more over heat...mike
    Michael Collins
    1993 4X4 Suburban
    many other toys as well

  5. #5
    Join Date
    Jul 2007
    San Jose, California


    Hi Guys,

    Thanks for the ideas. I know the system was flushed when the new radiator was put in (at least I was charged for

    50/50 antifreeze/water
    No pressure check on the system or cap - will do that
    Water pump is working as far as I know. Not sure how to check
    Fan seems to be ok, can't see any noticable wobbling
    Transmission shifts fine
    I have about 114K miles on it. The guy who owned it before me put on an Edlebrock intake manifold and headers. He didn't do any internal work on the motor. It runs well, doesn't burn oil. So, I don't think I need a rebuild at this time.

    As for the clutch fan, I will have to look into that as I am not sure. I think it is working

    Thanks again for the suggestions, you all rock!!

    Take care,


  6. #6


    Quote Originally Posted by dec7777 View Post
    As for the clutch fan, I will have to look into that as I am not sure. I think it is working

    The clutch fan could be suspect...I'm really diggin' Mike's Taurus fan swap idea myself.


    2007 Ford E250(Work van) (Ya, Ya, shut up!)
    1996 GMC Sierra SLE 1500 5.7L/4L60E

  7. #7


    Clutch fan is the most suspect item.
    Did the previous owner ever have a problem with running hot? Twice now I've seen engines with aftermarket manifolds run hot. One was due to bad casting designs causing a reduced flow in the cooling system and the other was by an installation screw up when the installer left some gasket material over a passage that needed to be open.

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