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[GMCnet] Cooling System Flush Procedure [message #247979]

Sun, 20 April 2014 17:42

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

G'day,

I forgot I had promised to do this awhile back! Bob de Kruyff sent me a summary of how he flushes the engine cooling system in his
GMC and I put together this step by step procedure.

GMC COOLING SYSTEM FLUSH PROCEDURE

Background: The cleaner a cooling system in a vehicle is the better it will perform. The following procedure will outline how to
flush the engine cooling system in a GMC Motorhome to have it perform at its best.

MATERIALS REQUIRED

Oxalic Acid Crystals:

Amazon: http://tinyurl.com/koz3krz

http://www.amazon.com/Oxalic-Acid-99-bag-C2H2O4/dp/B007HUR0EK/ref=pd_sim_sbs_hg_1?ie=UTF8&refRID=1J7JJW7SR89088HPWR2T

eBay: http://tinyurl.com/mjwwpez

http://www.ebay.com/itm/Oxalic-Acid-99-pure-2lb-/261334376485?pt=LH_DefaultDomain_0&hash=item3cd8be2025

Baking Soda - Local purchase

Distilled Water - Local purchase

Anti-Freeze - Local purchase

PROCEDURE

1) Open any valve(s) installed in the lines to / from the heater core and to / from the house water heater.
2) Open the drain on the radiator to drain the cooling system and remove the anti-freeze water mix.
3) Close all drains and fill the system with fresh water.
4) Start the engine and allow it to run long enough to remove the air from the cooling system.
5) Shut off the engine and check the radiator and fill with fresh water as required.
6) Start the engine again and allow it to idle for a few minutes to verify that there is no air in the cooling system.
7) Shut the engine off and open the drain on the radiator to drain the cooling system again.
8) When water stops draining close the radiator drain valve.
9) Heat 2 quarts of water and dissolve 2 cups of oxalic acid crystals in the hot water.
10) Pour the oxalic acid / water solution into the radiator then fill the system with fresh water.
11) Start the engine and allow it to idle until normal operating temperature is reached.
12) Shut off the engine and allow the GMC to sit for a couple of hours.
13) Start the engine and take the GMC for a drive until it reaches full operating temperature.
14) Return home and drain the cooling system.
15) Fill the cooling system with domestic water while leaving the radiator drain open and the radiator fill cap off.
16) Regulate the input water so that the radiator stays full with the drain open and radiator fill cap off.
17) Start the engine and allow it to idle with radiator drain open and the radiator fill cap off.
18) When the drained water becomes clear stop the engine and shut the radiator drain.
19) Heat two quarts of water and dissolve 4 cups of baking soda in the hot water.
20) Pour the dissolved baking soda / water solution into the radiator and fill the system with fresh water.
21) Start the engine and allow it idle until it reaches normal operating temperature.
22) Shut the engine off and open the radiator drain valve.
23) Drain the cooling system.
24) Close the drain and fill the system with fresh water.
25) Start the engine and allow it idle until it comes to normal operating temp.
26) Shut the engine off and drain the cooling system.
27) Fill the cooling system with 50/50 antifreeze / distilled water.

Please feel free to review this procedure and comment if something is not clear, you disagree with anything I've noted, or have
anything to add or subtract.

Regards,
Rob M.
USAussie

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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426