Overview

Links on this page:

• General overheating issues
• Fan timer runs continuously solution
• What to do when your Honda overheats, troubleshooting/solution
• The importance of bleeding 
      how to bleed
• Sensor locations
• Radiator fan won't come on troubleshooting
      How to check a fan switch
      How to check a fan relay  
          >relay test
      How to check a fan
      How to check the fan's input ground
      How to check the fan's input battery power
      How to check the cooling system wiring circuit (final step)
• How to bleed the cooling system 
• How to test a thermoswitch (fan switch)
• How to test a thermostat
          How to troubleshoot a thermostat
• How to prevent the plastic radiator from cracking
• How to buy radiators
• Technical details

Problem: The fan runs continuously (longer than 19-minutes) when the key is removed. The symptom is a dead battery. The fan turns off only when the ignition is turn off then on. 99% chance the fan timer is bad. Usually happens to the 90-93 Accords.

Solution: The reasonable solution is a replacement of the timer control unit. Before a replacement it would be wise to troubleshoot. When the fan does not turn off after 15 minutes swap the cooling fan relays in the engine fuse compartment with another identical relay. If the fan refuses to turn off replace the fan timer unit.

Replacement:  Remove the access panel on the driver's kick panel and search for a box way in there the size of two cigarette packs with 8-terminals. The 86-89 Accord fan timer unit is located under the passenger seat. Unbolt the unit and swap it with a new one.

Note: the fan timer location is a bit more to the right compared to this image. It's right next to the main relay like this image (as seen the main relay removal page.)

Problem: General overheating issues. An overheating engine is characterized by the climbing of the needle which may eventually reach the red mark on the temperature gauge. The normal operating temperature of a normal Honda is 89-90-degrees Celsius. During hill climbing the needle may climb but it's not considered to be overheated if the needle doesn't reach the red mark. 

The owner should first check for the most accessible and simplest problems. Here are some overheating problems you should check for:

• Are coolant flow blocked?
• Is the thermostat stuck-closed?  
• Is the thermostat broken? symptoms, troubleshoot, test
• Is the thermostat missing?
• Has the air been purged (thru the bleed bolt)?
• Is the fan relay working?
• Is the fan switch working?
• Is the fan working?
• Is the radiator cap working? Releasing fluid? Evaporation thru a broken cap?
• Is the radiator holding pressure? (leakage?) Solder or seal joints bad?
• Is the timing correct?
• Are the radiator fins blocked from bugs?
• Is the radiator clogged from corrosion?
• Is the radiator expelling pressure  (Head gasket problem?) or evaporating from the exhaust manifold?
• Is the cooling system hoses leaking? Thru pinhole leaks? Look for white dried splash marks inside the engine bay.

SCHEMATIC

90-93 Accord fan timer unit is under the dash, right next to the main relay. It's the size of two cigarette packs. 86-89 Accord fan timer unit is located under the passenger seat the size of a cigarette pack. CRX cooling system diagram (below)

Left Figure 1. 90-93 Accord circuit shows wired connections between the ECU, timer and sensors and relays.

Whenever the needle climbs past the normal mark while idling or at a low speed on flat road, follow these steps to troubleshoot:

1. While the vehicle is going towards overheating, turn on the A/C. (Tip: turning the heater dial and the heater fan to its maximum may aid in the cooling of the engine.) If the temperature continues to climb, turn off the AC and follow step 2 immediately. If the temperature drops while the A/C is on, leave the A/C on and drive to a service station or drive home then check the water level or check the fan switch, otherwise follow step 2.

2. Pull over in a safe spot while the needle continues to climb to the red mark and shut off the motor. If you need to continue driving, wait until the needle falls below the red mark. (DO NOT allow the needle to be at or above the red mark for an extended period with the motor running. The damage may or may not be immediate. ) 
   
   

3. Turn the ignition to ON, not start.  Peer under the car while sitting in the driver seat. You will feel a gush of hot air if the fan is working. 

4. Raise the hood to cool down the motor and confirm that the fan is running.
   
    CAUTION:   For your safety, move away from the hood of the car after raising the hood to avoid any sudden hose or tank bursting. Tank rupture usually occur a few seconds after the engine turns off. 

5. Patiently watch the needle until the needle points to the normal operating temperature mark. This will confirm that the temperature needle is working.  (Avoid adding coolant until the temperature cools down completely.)

6. When the temperature is this high the fan(s) will run with the ignition on but will also run with the ignition off on cars with a fan timer. Check the fans while the ignition is on or off. If the fan isn't on turn off the ignition to allow the automatic fan to kick in, otherwise leave the ignition on for no more than 15 minutes.
   
   Next, place your hand on the upper hose and the lower hose and feel the temperature difference. (Caution: Female's pain nerve receptors are much more sensitive than the male's pain receptors - use common sense.) If there is a difference then the thermostat is most likely dead.  CAUTION:   Avoid the automatic start fans.
   
   If the water level is low (visible from the reservoir) allow the temperature gauge to drop below the COLD mark. Place a rugged rag over the filler cap and loosen the cap only one click and then proceed to remove the cap slowly when it is safe to do so. Start the engine and refill the reservoir and filler neck with the proper mix of coolant and water then close the cap tightly. If there is coolant leaking due to a crack radiator or a serious hose leak put the cap on but don't close the cap to avoid loosing coolant rapidly. Finally, and at your convenience, follow the refilling and bleeding procedure at the bottom of the page.
   
     WARNING:   Risk of scalding yourself and bystanders. Risk of eye exposure.  Removing the cap on a hot motor under pressure can send coolant flying at a radius of 15 feet. Always allow the engine to cool down completely and always use a rag to cover the filler neck before opening.
   
   

7.  Thermostat troubleshooting:   On a cool motor and the coolant at the proper level, start the motor and allow the engine to warm. Feel the upper radiator hose leading to the engine. You should feel a surge of warm coolant (within minutes) when the thermostat opens. If you don't feel the surge then remove the thermostat and boil it in a pot. If the thermostat passes the pot boiling test then check for a poor water circulation in the cooling system. 

8. Coolant flow troubleshooting: Open the filler cap. If the coolant refuses to flow normally at the filler neck, bleed the coolant, check for a clogged radiator, check for an eroded water pump impeller or test the thermostat. If the coolant flows but bubbles are also seen flowing along with the coolant then most likely the head gasket is broken. The head gasket failure indicates that the engine has undergone overheating in the past. The solution is to replace the head gasket after confirming it with a leak down test. 

9. Overheats at high speeds: If the car overheats at high speeds then most likely the timing is off, the engine is lugging, fins blocked by bugs or the coolant is low. 
   
   

Problem: A common problem for the third generation Accord is the crack on the upper plastic radiator tank. The crack will cause a major leak in no time unless the cap is open to relieve pressure while driving the vehicle. The crack forms a 3" external crack but will be about 8" on the inside. The nylon is crystalline and crumbly on the inside. 

Solution #2: Keep your cooling system in good shape and the coolant level correct. An overheating engine or a low coolant level increases the odds of cracking the plastic radiator.

Solution: #3: Some of the ideas from the extreme DYI car owners use glue. To see how this is done see gluing radiator page.

Solution: #4: Some of the ideas from the DYI car owners use a 10-11 gauge stainless steel "C" braces. See image below.

Areas of the crack viewed from the front of the vehicle.

Problem: Water is leaking from the right side of the timing belt cover, the water pump weep hole or from below the timing belt cover. Coolant is found on the ground.

Solution: Replace the water pump seal or the water pump. Prevention: By changing the coolant at their recommended interval and using a coolant made by Honda is said to slow down the decay of the water pump seal. The decay is shown in the two linked images below (seal A, B.)

Water pump exploded view. View images of seal A and seal B . The two seals can be replaced if they are available. The bearing seal and other seals aren't affected.