Procedure to Drain, flush, and refill coolant

1. Move heater "Temp" control lever all the way to "Hot" position.
2. Remove undercover.
3. Open drain plug at the bottom of the radiator, and remove radiator cap.
4. Remover drain plug on cylinder block. -coolant is removed-
5. Close drain plug and tighten drain plug securely. -apply sealant to the thread of drain plug-
6. Open air relief plug.
7. Fill radiator with water and close air relief plug and radiator cap.
8. Run engine and warm it up sufficiently.
9. Race engine 2 or 3 times under no-load.
10. Stop engine and wait until it cools down.
11. Repeat step 2 through step 9 until clear water begins to drain from radiator.
12. Drain water.
13. Open radiator cap and air relief plug.
14. Fill radiator with coolant up to specified level.
15. Close air relief plug.
16. Remove reservior tank, drain coolant, then clean reservior tank.
17. Install reservior tank and fill it with coolant up to "Max" level and then install radiator cap.
18. Run engine and warm it up sufficiently.
19. Race engine 2 or 3 times under no-load.
20. Stop engine and cool it down, then add coolant as necessary.

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Quick Tip. After flushing your cooling system, make sure you fill up your cooling system completely. The KA24 engines seem to like to trap air in the system and needs to be bled completely. My friend and I both own 240sx's and after she had a mechanic flush her system, she noticed her car would overheat at idle. Upon inpecting the cooling system, I noticed there were no leaks, and no coolant. An easy way to bleed the system is to run the engine, and keep adding water/coolant into the  radiator while shaking various parts of the car. I liked to just push down on the front bumper. Shaking the front end side to side also helped. It took about 30 minutes of this to get all of the air out. At least as much as my body could take!

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P.S. This applies to SOHC and DOHC models.

Where is the coolant drain plug on the block?

It is on the left side of the engine (looking from the driver seat). It is very close to the O2 sensor below the exshaust manifold cover. You can not see from the top Rise the car slightly, and look up from behind the left front wheel and you should see it. It is a 14mm short bolt. It is hard to undo from underneath the car. However use about 6" extension and unscrew from the top. Make sure to wear safety glasses. This should be on all the S13.

Allen Alqadi
Email: [email protected]