4AGE 20V Blacktop

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Diary of Swap
Cooling System



85/6 4AGE -> 4AGZE

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Air Intake Filter
Clutch Slave Cylinder
Clutch Master Cylinder
Coolant Flush
Distributor O-Rings
Exhaust Manifold
Fuel Filter

Fuel Pump Cut-off Switch

Ignition Timing
Oil Cooler Hoses
Oil Filter Adapter O-Rings
Oil Pan Gasket
Oxygen Sensor
Radiator Removal
Throttle Body Cleaning
TPS Adjustment
Water Pump


87+ Brake Upgrade
Caliper Rebuild-Front
Caliper Rebuild-Rear
Dust Shield Removal
Parking Brake Cable
SS Braided Brake Line


Ball Joint Replacement
Bushings Install - Front
Bushings Install - Rear
Steering Knuckle Removal
Struts/Springs - Front
Struts/Springs - Rear
Sway Bar End Links


87+ Antenna Replacement
Clear Turn Signals - Front
Clear Turn Signals - Rear
Door Hinges
Interior Door Triangles
Interior Headliner Painting
Interior Trim & Light Lens
Power Window Regulator
Rekeying Trunk Lock
Rust PM - Battery Bracket

Rust PM - Front Wheel Wells
Seats - MK3
Seats - Aftermarket
Shift Boot
SideMarker Mod
Sunroof Rattle
Wiper Switch


2006 Austin
2005 Austin
2005 Topeka NA2005
2004 Galveston
2004 Chattanooga SE2004
2003 Galveston
2002 Austin


Suspension Setup Pics
My MR2 Diary
Latest Pics of My MR2

Water Pump Change (Part 3/3)

Page 1, 2, 3

Flushing the coolant system

Here's what I found to be the simplest for me. There are a few other ways to do this, e.g. using the radiator drain cock. But the drain cock on mine is plugged, so that didn't work.

1) Remove the drain bolt on the coolant pipe going from the radiator cap to the radiator, the red circled one below (leave the other bolt on, unlike the below pic). Then without the car running, the rear of the car higher than the front, place a garden hose at the radiator cap, and begin running water through. Run the water through, until it becomes clear. Of course this may take a few pan-fulls. So watch the level of the pan closely. A second person to run the hose while you monitor the pan during this entire process helps tremendously. Be prepared to get your hands dirty when placing the bolt back on as it is still draining out and your pan is full. Replace the bolt when done.


2) Next up is flushing out the radiator. (This can get messy, and it is possible to skip this step if you don't want to clean up after yourself) Remove both upper and lower hoses on the radiator, by moving the spring clips. Then place the garden hose into the upper hole in the radiator, draining the water out of the lower one. Flush it until clear water comes through, and then replace the hoses.


3) Now, use the drain bolt on the coolant pipe, that leads to the thermostat (red circle, leave the other bolt on, unlike shown in the below pic). Run the garden hose from the radiator cap flushing out the system from the radiator cap, up through the radiator and back halfway under the car. Again, once it turns clear you're done with this step. Replace bolt.


4) Now for the engine block and the rest of the way up this pipe. Make sure all coolant bolts and hoses you removed before are securely fastened. Fill up the system with water from the garden hose, until it's full in the radiator cap. Start up the car, with the heater control set to hot (no need to turn the fan on). Monitor the level in the radiator cap to keep it topped off. Once you see the water start to bubble over, place the radiator cap on halfway (to the first click). When the car approaches normal operating temperature, it is time to remove one of the coolant pipe drain bolts. (mine was about 2/3 the way up to normal operating temp when I undid the bolt) Have the person that is running the hose, be ready for when you remove the bolt, you would like to keep the coolant level topped off. Be very, very careful when undoing the bolt. The coolant will be hot and it will come out of the hole fairly quickly. I'd suggest wearing a good set of gloves when doing this. Just make sure not to drop the bolt in the pan. When the pan is almost full, replace the bolt. Again this will be messy, and the coolant coming out of the hole will be hot. Empty the pan and keep the garden hose running to top off the level. Once the pan is empty, position it again and undo the bolt, repeating this entire process till the water is clear. After a few times, the coolant cools down from the constant running of the garden hose water running through. So it becomes less painful...

Now repeat this process again, but with the other bolt on the coolant pipe. It won't take near as long doing this one. Keep the car running during this entire process, making sure to keep the coolant level topped off.


Here's a pic of the first night of flushing the system, over 8.5 gallons. About 2.5gallons came from draining the car initially (I ran out of containers). This was the morning after, before taking the containers to empty at the local recycling center. Once you notice that the coolant is starting to thin out it is probably safe to dump in your yard. Don't quote me on that, save the environment...


5) When you are satisfied with the color of the water coming out of the coolant pipe, turn the car & garden hose off, and drain as much of the water out as you can. Then start filling the system with the Toyota coolant. Follow the repair manual for the filling procedure. Below is just a pic of the Toyota coolant mixed with water, 50/50.


Overall, this wasn't too terribly bad a project. It was my first 'big' repair on my '2. I worked on it for 3 nights after work. I screwed up the first night, installing the pump and had major leakage when I went to fill it up with water. The second night tearing everything apart and putting it back together again was really easy as I knew what all had to come out and how to get to everything. I also started the coolant flush the second night, filled the system with the Prestone Coolant Flush, and drove to work the next day. The third night was spent flushing the coolant system completely and thoroughly. This time I had a friend help me which sped up the process alot. I would figure a good long weekend day to do this, especially if you are going to flush the system out well and if you haven't done the water pump or timing belt before. But if I had to do it again, it would probably only take a few hours. Just be prepared to move from working under the car to working over the car to working under the car to ....

Hopefully, these instructions will help in giving an idea of what all needs to come out. That seems to be the biggest problem with the BGB. Good luck!

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Disclaimer: This web page in no way replaces the MR2 repair manual. Follow what it says before me. The purpose of this page is to give you a better pictorial description of what to do. I cannot be held responsible for any mishaps caused by this web page.