Hyundai Coupes/Sedans 1986-1993 Repair Guide

Engine Coolant



A good quality ethylene glycol based or other aluminum compatible antifreeze is recommended for use in the vehicles covered by this guide. It is best to add a 50/50 mix of antifreeze and distilled water to avoid diluting the coolant in the system.


See Figure 1

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Fig. Fig. 1: Use a float type tester to check the coolant

Allow the engine to cool down. Using a rag, turn the radiator cap 1/4 turn to the stop and allow all pressure to escape. Then, remove the cap. Check the level visually in the expansion tank. It should be above the low mark. Never fill the tank over the upper mark. Fill the radiator until the level is within 25mm (1 in.) of the radiator cap. It is best to add a 50/50 mix of ethylene glycol antifreeze and water to avoid diluting the coolant in the system. Use permanent type antifreeze only. Avoid using water that is known to have a high alkaline content or is very hard, except in emergency situations. Drain and flush the cooling system as soon as possible after using such water.

Cover the radiator cap with a thick cloth before removing it from a radiator in a vehicle that is hot. Turn the cap counterclockwise slowly until pressure can be heard escaping. Allow all pressure to escape from the radiator before completely removing the radiator cap. It is best to allow the engine to cool if possible, before removing the radiator cap. After filling the radiator, run the engine until it reaches normal operating temperature, to make sure that the thermostat has opened and all the air is bled from the system.

Testing for Leaks

See Figures 2, 3, 4, 5 and 6

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Fig. Fig. 2: Remove the recovery tank cap to allow the pressure tester to be connected to the system

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Fig. Fig. 3: This cooling system requires a threaded adapter for the recovery tank to allow the pressure tester to be connected

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Fig. Fig. 4: Thread the adapter onto the recovery tank

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Fig. Fig. 5: Pump the cooling system with pressure, making sure not to overpressurize the system or damage can occur

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Fig. Fig. 6: Watch the gauge on the system and observe the pressure reading

If a the fluid level of your cooling system is constantly low, the chances of a leak are probable. There are several ways to go about finding the source of your leak.

The first way should be a visual inspection. During the visual inspection, look around the entire engine area including the radiator and the heater hoses. The interior of the car should be inspected behind the glove box and passenger side floorboard area, and check the carpet for any signs of moisture. The smartest way to go about finding a leak visually is to first inspect any and all joints in the system such as where the radiator hoses connect to the radiator and the engine. Another thing to look for is white crusty stains that are signs of a leak where the coolant has already dried.

If a visual inspection cannot find the cause of your leak, a pressure test is a logical and extremely helpful way to find a leak. A pressure tester will be needed to perform this and if one is not available they can be purchased or even rented at many auto parts stores. The pressure tester usually has a standard size radiator cap adapter on the pressure port, however, other adapters are available based on the size of the vehicle's radiator neck or recovery tank depending on where the pressure tester connects. when pressurizing the cooling system, make sure you do not exceed the pressure rating of the system, which can be found on the top of the radiator cap, however, if you have and aftermarket or replacement cap that does not have the rating on it, 16psi is a standard to use but some cars are higher. Overpressurizing the system can cause a rupture in a hose or worse in the radiator or heater core and possibly cause an injury or a burn if the coolant is hot. Overpressurizing is normally controlled by the radiator cap which has a vent valve in it which is opened when the system reaches it's maximum pressure rating. To pressure test the system:

The pressure test should be performed with the engine


  1. Remove the radiator or recovery tank cap.
  3. Using the proper adapter, insert it onto the opening and connect the pressure tester,
  5. Begin pressurizing the system by pumping the pressure tester and watching the gauge, when the maximum pressure is reached, stop.
  7. Watch the gauge slowly and see if the pressure on the gauge drops, if it does, a leak is definitely present.
  9. If the pressure stayed somewhat stable, visually inspect the system for leaks. If the pressure dropped, repressurize the system and then visually inspect the system.
  11. If no signs of a leak are noticed visually, pressurize the system to the maximum pressure rating of the system and leave the pressure tester connected for about 30 minutes. Return after 30 minutes and verify the pressure on the gauge, if the pressure dropped more than 20%, a leak definitely exists, if the pressure drop is less than 20%, the system is most likely okay.

Another way coolant is lost is by a internal engine leak, causing the oil to be contaminated or the coolant to be burned in the process of combustion and sent out the exhaust. To check for oil contamination, remove the dipstick and check the condition of the oil in the oil pan. If the oil is murky and has a white or beige "milkshake" look to it, the coolant is contaminating the oil through an internal leak and the engine must be torn down to find the leak. If the oil appears okay, the coolant can be burned and going out the tailpipe. A quick test for this is a cloud of white smoke appearing from the tailpipe, especially on start-up. On cold days, the white smoke will appear, this is due to condensation and the outside temperature, not a coolant leak. If the "smoke test" does not verify the situation, removing the spark plugs one at a time and checking the electrodes for a green or white tint can verify an internal coolant leak and identify which cylinder(s) is the culprit and aiding your search for the cause of the leak. If the spark plugs appear okay, another method is to use a gas analyzer or emissions tester, or one of several hand-held tools that most professional shops possess. This tools are used to check the cooling system for the presence of Hydrocarbons (HC's) in the coolant.


To drain the cooling system, allow the engine to cool down BEFORE ATTEMPTING TO REMOVE THE RADIATOR CAP. Then turn the cap until it hisses. Wait until all pressure is off the cap before removing it completely.

  1. At the dash, set the heater TEMP control lever to the fully HOT position.
  3. With the radiator cap removed, drain the radiator by loosening the petcock at the bottom of the radiator. Locate any drain plugs in the block and remove them. Flush the radiator with water until the fluid runs clear.
  5. Remove the expansion tank and drain it.
  7. Close the petcock and replace the plug(s), then refill the system with a 50/50 mix of ethylene glycol antifreeze. Fill the system to 25mm from the bottom of the filler neck. Reinstall the radiator cap.
  9. Install the expansion tank and fill it to the FULL mark with pure antifreeze.
  11. Operate the engine at 1,500 rpm for a few minutes and check the system for signs of leaks.


See Figures 7 and 8

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Fig. Fig. 7: Check the radiator cap's rubber gasket and seal for deterioration

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Fig. Fig. 8: Radiator cap operation

Allow the engine to cool sufficiently before attempting to remove the radiator cap. Use a rag to cover the cap, then remove by pressing down and turning counterclockwise to the first stop. If any hissing is noted (indicating the release of pressure), wait until the hissing stops completely, then press down again and turn counterclockwise until the cap can be removed.

Check the condition of the radiator cap gasket and seal inside of the cap. The radiator cap is designed to seal the cooling system under normal operating conditions which allows the build up of a certain amount of pressure (this pressure rating is stamped or printed on the cap). The pressure in the system raises the boiling point of the coolant to help prevent overheating. If the radiator cap does not seal, the boiling point of the coolant is lowered and overheating will occur. If the cap must be replaced, purchase the new cap according to the pressure rating which is specified for your vehicle.

Prior to installing the radiator cap, inspect and clean the filler neck. Make sure that the stop tabs are straight. If not, straighten them with needle nose pliers. If you are reusing the old cap, clean it thoroughly with clear water. After turning the cap on, make sure the arrows align with the overflow hose.


See Figure 9

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Fig. Fig. 9: Keep the radiator fins clear of debris and keep the fins straight

Periodically clean any debris leaves, paper, insects, etc. from the radiator fins. Pick the large pieces off by hand. The smaller pieces can be washed away with a water hose.

Carefully straighten any bent radiator fins with a pair of needle nose pliers. Be careful as the fins are very soft. Don't wiggle the fins back and forth too much. Straighten them once and try not to move them again.