Water is not going to get up there by the thermostat. There will not be anything there to flush anyway. The biggest concerns are clearing the heater core, block, and radiator. Those are the places where stuff will settle.
A lot of GM vehicles have heater cores with plastic nipples that are easy to break. It is better to remove a heater hose from the engine than from the heater core. Run water from a garden hose into the heater hose, then into the port you removed it from.
It is also a good idea to avoid opening the petcock on the radiator unless you have done it before without a problem. Most radiators now have plastic tanks, and it is too common for the sealing surface to crack when the petcock is push back into place. Then you will have a drip about once every five seconds. The only fix for that is to replace the radiator. I prefer to pull of the lower radiator hose once I am done with the flush.
You will have to work a little harder if you do not have a radiator cap. GM's engineers left them off most of their vehicles. Fill the reservoir, then let it overflow through the radiator to drain out. Siphoning action should empty it. On other brands of vehicles, I leave the reservoir empty but I fill the rest of the cooling system. There will be at least half a gallon of water that won't drain out. Start by filling a gallon of straight antifreeze. When it is up to me, I never use the red Dex-Cool, (Dex-Mud). Next, add a gallon of water. Alternate like that to get close to a 50/50 mix. Run the engine to mix the coolant, then check the freeze point. Now you have the empty reservoir to add whichever is needed to bring it to minus thirty five degrees.
Be aware too that most freeze point testers that use something that floats are measuring the weight of the coolant in relation to the weight of water. Straight antifreeze will show up that way as freezing at an unreasonably-low temperature. In reality, straight antifreeze freezes at around minus ten degrees. The freeze point goes lower when water is added, but only to a certain point. The lowest freeze point is achieved with seventy percent antifreeze and thirty percent water, but antifreeze does not hold as many BTU's of heat as water does. You need enough water to carry the heat to the radiator. You need enough antifreeze to get the anti-corrosion and water pump lubricant additives in it.
Watch for signs of overheating when you first run the engine. V-6 and V-8 engines do not usually have a problem with that, but if an air pocket forms under the thermostat, it will not open. Thermostats have to be hit with hot liquid to open. Hot air will not do it. When this happens, there will be a bleeder screw on the thermostat housing, or there will be a temperature sensor or threaded plug that can be removed while you are filling the system. If you have to unplug a sensor to remove it, leave the ignition switch off to prevent setting a diagnostic fault code that could confuse someone in the near future.
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Sunday, August 13th, 2017 AT 2:33 AM
