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How to Drain & Flush the Engine Coolant
1990-1994 Lexus LS400

By LexLS.com

Before doing anything read my disclaimer & safety info.



Make sure you prepare for this one, it's not too hard but does take a while. I filled with Prestone Extended life coolant and 2 gallons of distilled water. You can also fill with the Toyota red coolant which is probably a better choice.

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Tools Needed:

Parts/Supplies Needed:

1) Put the car on ramps. Jacking up the car and putting it on jack stands will not give you enough room to work. Ramps give you more room, even though it's not that much.

2) Remove the 11 10mm bolts that hold the engine under cover and set the cover aside.

There are 3 drain cocks that you need to get at in order to properly drain the coolant. This is the front drain cock; it's located directly under the radiator towards the right side of the car.

Here is the right drain cock.

Here is the left drain cock. This one is much harder to get at because the steering rack and O2 sensor are in the way.

Close-up of the left drain cock. You can see it's the same as the right one.

3) Wait until the engine has cooled down, then unscrew the coolant cap. Here you can see that my coolant was the typical green color, this is not the right stuff for an LS. It should be a red/orange color.

4) Using a pliers, unscrew the front drain cock. This will start draining your coolant.

5) Using a 17mm socket, unscrew the filler plug from the water inlet housing. I know the repair manual says to do this first, but I tried it that way and it starting overflowing. I found that it's better to start the draining and then open this up. Remember not to lose the gasket!

6) Attach a section of 3/8" inner diameter vinyl tubing to the right drain cock and direct the tube into the drain pan. Then open the drain cock using a 14mm socket; just enough so the coolant can flow out, do not remove the bolt.

7) Open the left drain cock using the same procedure described in #6 and wait for all the coolant to drain out.

8) Close all 3 drain cocks. Torque the engine drain cocks to 18 ft-lbs (250 kg-cm, 25 Nm).

Skip steps 9-15 if you don't need to do a flush.

I used Prestone Super Radiator Flush to flush all the contaminates out of my cooling system.

9) Add the entire bottle of flush treatment into the water inlet housing.

10) Slowly fill up the rest of the water inlet housing with water. Put in about 2 gallons of water here and then replace the gasket & plug on the water inlet housing.

11) Slowly add water to the reservoir tank until it is full.

12) Start the car and turn the A/C control temp to the highest temperature (85 degrees). Check in the engine bay to make sure that the heater control valve is fully open (fully open in pic) and continue adding water to the reservoir until it no longer drops. Then replace the reservoir tank cap. The system capacity is 11.2 quarts (2.8 gallons).

13) Follow the instructions on the flush bottle. Basically you need to let the engine run for about 10 minutes so the chemical has a chance to run through the system. Stop the engine at the specified time. Take a break and let the engine cool down. It will be VERY hot and you don't want to burn yourself on the engine or coolant.

14) Once the engine has cooled down it's time to drain out the flush chemical and water mixture; repeat steps 3-8. Have some shop rags handy because foaming/bubbling may occur when you open up the water inlet housing plug. I added some extra water while all 3 drain cocks were open and everything was draining to reduce the bubbles.

15) Fill with water only, steps 10-12. This time only run the engine for a few minutes so the water has a chance to run through the system, then stop the engine. Repeat steps 3-8 to drain the water. At this point the water that drains out should be clear.

16) Now that your system has been flushed it's time to add the new coolant and water mixture. Slowly add one gallon of coolant and one gallon of distilled water to the water inlet housing (50-70% coolant recommended). Slowly continue to fill the water inlet housing with water & coolant until it is full.

17) Replace the gasket and torque the plug of the water inlet housing to 33 ft-lbs (450 kg-cm, 44 Nm).

18) Slowly add the 50-70% coolant and distilled water mixture to the reservoir tank until it is at the upper line.

19) Repeat step 12 using the coolant and water mixture. The level of the reservoir will drop after a while. Add the mixture until the level no longer drops and then replace the reservoir tank cap.

20) Stop the engine after racing it for 5 minutes at 2000-3000 RPM.

21) Take a break while waiting for the coolant level to drop. Once the coolant level drops open the reservoir tank cap and add the coolant/water mixture until it is just below the overflow line. Tighten the reservoir tank cap.

22) Replace the engine under cover.

23) Monitor the coolant level and check for leaks over the next few days. I checked and filled mine in the morning before I used the car. Add more coolant/water if necessary.

**Bring the old coolant into your local auto shop or county recycling center for proper disposal.
DO NOT dump it in your backyard or down the drain!!!**



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Last revised: Sunday, 29-Oct-2023 15:46:19 EDT