Whether you are trying to catch up with some long overdue maintenance or trying to ready a used car purchase for use there are times when corrosion buildup in your cooling system can effect its performance and place a burden on the engine, water pump, radiator, thermostat and heater core. This type of service is not for normal changing of old coolant it is for a system that has a significant amount of Rust.
What you will need to complete the flushing of your cooling system.
New Radiator Coolant to replace the old
Cooling System Flush
New Thermostat and Two Gaskets
Basic Tool Kit
Garden Type Hose for Running Water
Draining Your Vehicle’s Cooling System
The first thing that you need to do is drain the system of old coolant by draining what you can from the radiator. With the engine cool place a large pan under the radiator and open the petcock valve to release fluid from the radiator. Opening the cap on the radiator will allow the radiator coolant to flow quicker. Discard the old coolant properly by placing it in jugs and bringing it to a garage or drop off point do not pour it down your house drain.
To flush the remaining coolant from the system you will need to fill the system with water however unless the system is brought up to temperature the thermostat will impede the flow of water through the system. This means the process will take much longer if you have to fill, run the car to temperature and drain and fill and drain and it will also not be as effective. The best result for very heavy corrosion would be to remove the thermostat during the flushing process and then replace it with a new one because it has probably been compromised anyway. When you remove the thermostat and replace the housing then it is best to use a new gasket. Since you will need another new gasket when you have completed the flushing to install the new thermostat you should ask for 2 gaskets when you buy your new thermostat.
Beginning the Cooling System Flushing Process
To drain the remaining Coolant and remove a majority of rust you should place a running hose into the radiator fill spout. Remove the cap and then open the drain petcock then adjust the flow of the hose to match that of the draining water so the radiator remains full during the flushing process. You might need to make adjustments as you go to make sure the radiator remains completely full with a supply of fresh water.
Run your engine and observe the draining fluid by placing a catch pan under the radiator and sampling the water as you go. It is not that important that you catch all of the coolant as anything remaining will be highly diluted as the flushing process continues.
When the water starts to come out clean then you know a good portion of the bad coolant and rust has been removed.
Using a Cooling System Flush Product
At this point to have a better result it is suggested that you close up your petcock and add a flushing fluid that can run through your system to remove remaining contaminants. Read the directions on the container on how it should be used.
Normally you will run the engine for 10-15 minutes and let it sit. I suggest you let the engine run until hot air is flowing out of your heater for about 10 minutes. I know some people that will drive the vehicle for a day but I don’t suggest that. However you probably would benefit from it sitting in the cooling system for a few hours if you have the time.
After the system has been circulated with cooling system flush you need to go through the draining and flushing process again. Run the vehicle with water flowing into the radiator from a garden hose and draining out of the petcock until it runs clean.
Drain as much water out of the system as you can, install your new thermostat and then refill with coolant.
Don’t forget to bleed the system of air or you could have overheating issues.
Final Note
You should always follow manufacturer’s directions when performing maintenance on your vehicle. If your vehicle is under warranty then you should at least have a conversation with your Manufacture’s Service Department before you decide to do the work yourself.
When there is a heavy buildup of rust in your cooling system it can cause damage that a flush will not cure however cleaning out old coolant and flushing the system can restore more performance to your engine’s cooling system.
Other considerations you might have are changing water temperature sensors and your water pump. If your water pump is driven by a timing belt then replace the belt and idler pulley along with the belt as they come in kits and all should be replaced at the same time. Never change the water pump and put an old timing belt back on the engine.
Other damaged parts might be your radiator and heater core. You should see significant improvement but if they are clogged heavily with deposits then they may need to be replaced.
Run the vehicle for a few days and check the quality of the coolant and then check again every few weeks. If the problem returns then you can try performing the flush again but if you can not cure it then you may need to replace other parts.
Do not skip over changing a $15 thermostat only to have it stick open or closed because overheating may result in you needing a tow which will cost much more.