Question about 1991 GMC Sonoma

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How do i install block heater in 91 2wd 4 cyl sonoma

Not sure how to install block heater, do i need to drain all the coolant? i am mechanically inclined so dnt want to go to a shop. should be straight forward just looking for advice/directions thanks

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Hi ryan, yes my friend the best bet is to drain the coolant,as for the block heater,not sure which side for the sonoma but basically it is a frost plug with and internal element attached to it,once you unplug the cord typically there will be a small screw to remove, use a small punch or whatever will work and pop one side to roll the block heater so you can remove it,simple my fried,by the way a new block heater will come with installation instructions :) have fun and good luck ryan take care.

Posted on Nov 13, 2008


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Where is the block heater cord on my 91 oldsmobile cutlass

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Removal & Installation

Factory block heaters are not installed on these models. If an aftermarket heater has been installed the following procedure will most likely work. There are two basic types, one for the oil and one for the coolant. The oil heater usually just slips into the dipstick tube or replaces the oil drain plug. The following procedure is for the coolant type.

  1. Remove the negative battery cable.
  2. Drain the cooling system.


When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Remove the block heater in the same way as the freeze plugs. Some heater units have a bolt that must be loosened or a V-Clamp that must be removed to remove the heating element.
  2. Disconnect the heater connector and remove the heater element.

To install:

  1. Coat the new heater with sealant, then install the reverse order of removal.
  2. Fill the engine with coolant, connect the battery cable. Start engine and check for leaks

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hello. on the drivers side of radiator is a drain. here is a picture and the instructions for draining the coolant out.

  • Install a tube on the radiator drain. Place the end of the tube in the drain pan.
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  • Completely open the radiator drain ****.
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  • Place a drain pan under the block drain hole plug.
  • Remove the drain hole plug from the engine block.
  • Allow the coolant to drain from the block until the flow stops. There may be more drainage from the radiator at this time.
  • Install the block drain hole plug.
  • Close the radiator drain ****.

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    Jul 04, 2010 | 1997 GMC Suburban

    1 Answer


    1. drain coolant
    2.remove instrument panel
    3. for 5.4 (4v) if equiped,remove junction splash shield
    4.for 5.4 (4v) if equiped, disconnect starter relay cable9ad8eea.gif
    1. For 5.4L (4V), if quipped, remove junction block bracket.
    2. Clamp inlet and outlet heater hoses.
    3. Disconnect heater hose from heater core by gently pressing it toward heater core.
    4. Remove A/C plenum demister adapter.
    5. Disconnect vacuum line.
    6. Remove 13 plenum chamber top screws.
    7. Remove blend door assembly from case.
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    To Install:
    NOTE: If needed, clean and lubricate coolant hoses with plain water.

    1. Install heater core.
    2. Install blend door assembly to case.
    3. Install 13 plenum chamber top screws.
    4. Connect vacuum line.
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    6. Connect heater hose to heater core.
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    I have a 1999 GMC Sonoma and I had this problem very recently, This is a common problem with your radiator.

    - Something for you to check is and hour after your last drive (to let the engine cool down) open the radiator cap. Be careful. It may be pressurized and it may spray. If there is radiator fluid at the top, you should consult a mechanic. Otherwise a fix is easy:
    - If there appers to be no fluid, simply find a friend to give you a ride and go to your local auto store (Canadian Tire, Partsource, or their american equivilents).
    - Get a container (4 ltrs or 1 qrt) of 50/50 premix radiator coolant. Make sure it's a 50/50 premix. If you are unsure, as a clerk.
    - Once you get home, pop your hood and open the radiator cap again.
    - Pour the mixture in until it gets to the top.
    - With the radiator cap off, start your engine. This will circulate the coolant through the engine. As it does, coolant will drain out of the radiator and into the engine block.
    - You need to keep adding coolant to maintain a full radiator.
    - When it looks like no more coolant is going into the engine, put the cap back on and go for a drive.
    - Check that the heat is working. If so, Good Job!
    - If not, you may have to consult a mechanic.

    Hope this helps.

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