I top off my 1998 Nissan Altime's engine coolant evreyday. Also, the radiator fan stays on for appromiately 2 minutes after I shut the engine off. Is something wrong with the cooling system or the radiator?

fans are designed to run on after you shut engine down as engine temperature rise after switching off . running hot could be caused by the top hose having gone soft when you rev the engine the water pump sucks the hose flat stopping the coolant flow or the radiator is blocked and need flushing out

Raise the car front end as high as possible with a floor jack, fill the coolant tank to the top, run the engine until it reaches just short of overheating, shut it down and run water over the radiator, this will burp the air out. Repeat as needed. Don't let the coolant recovery tank run dry during procedure.

Its possible that your problem also stay in the Engine Coolant Temperature (ECT) sensor resistance changes in response to engine coolant temperature.

Keep in mindthat the sensor resistance decreases as coolant temperature increases. This provides a reference signal, which indicates engine coolant temperature, to the ECM.





Fig.: Compare the sensor readings with these values




Fig.: Location of the thermal sending unit (A) next to the coolant temperature sensor (B)

Keep us updated.

The ECM gets it messages for heat from the engine coolant temperature sensor. The sensor is probably bad. Since the fans come on right away the ECM is in a safe mode for the engine. Meaning it turns the fans on because it can't read the coolant sensor. As far as the fans staying on for a couple of minutes this is normal when the engine is hot. The ECM does this.

The fans are controlled by the Engine Coolant Temperature sensor mounted in the coolant hose at the top front of the engine. Disconnect the electrical connector and see what happens. Fans should not run. If that cut the fans off replace the ECT sensor.

The ECT sensor provides input to the Engine Control Module which controls the radiator fan ...Its usually the center sensor connector thats Grey..

When you run the engine, the coolant will remove heat and release it in the radiator. After you shut the engine off, the heat from the cylinders will still be there and the coolant will heat up some more. This is normal since there is no cooant circulating through the radiator.Without an actual temp gauge, there isn't any way of knowing just how much warmer it gets. I own a 1994 F 350 and have installed actual gauges. I can run my truck and watch the coolant temp. If I shut it off for up to 20 minutes, the gauge will go up ( sometimes as much as 20 degrees) when I start the engine, but return to the normal temps as the coolant is ciculated through the radiator.

Some cars are designed to have the fan run for a few minutes after you turn the car off. But if doesn't stop until the battery drains, then it might be a faulty switch or temperature sensor.

Or, if the fan stays running when the engine and radiator are cool you have a very cheap problem: The fan thermostat is stuck closed. A new thermostat will fix the problem--the hardest part of replacing it is finding it. Follow the wires from the fan to the switch--it is usually on the bottom tank of the radiator. Drain the radiator first and save the coolant to put back in after you replace the thermostat. NEVER OPEN A HOT RADIATOR.

If that wasn't it then check the following:

• Check to see that your coolant level is correct. Top up as necessary.
  
• Lay your hand on the radiator (with the engine off) and feel if it is as hot at the top as it is at the bottom. If not, your radiator may be clogged and need flushed or replaced. (Flushing is cheap. Replacing the radiator isn't)
  
• Do you get heat from the heater? Leave it turned on high and see if your fan stays running the next time. If it takes care of the problem that could mean you have a kinked radiator hose.

Hope this helped (remember comment and rated this).

When the car is completely cool,check the electric fan(s) for smooth rotation.

Clean/check/change the thermo sensor,contact and wire.

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Excavate air pocket in coolant system / check for head gasket leak

This test will kill two birds with one stone.

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MAKE SURE THE COOLANT SYSTEM and ENGINE IS COLD!

RAN THIS TEST IN A WELL VENTILATED AREA ONLY!

You will spill some coolant during this air pocket purge test.......BE KIND TO THE ENVIRONMENT and ANIMAL please clean up after the test!

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Put the front end on a pair of ramp or park your car on a VERY STEEP HILL (radiator facing top of the hill) .

Top of the coolant reserve tank

Let it ran for 10-15 minutes.

Monitor for air pockets escaping from coolant reserve tank.

Small amount of bubbles is OK at 1-5 minute mark

After the thermostat open up (after 195 F warm up) at
5-12 minute mark or after high idle you should see less bubbles.

If you do not see any in rush of bubbles then your thermostat may be partially stuck or rusted badly inside the thermostat hosing.

Give the thermostat host few gentle taps.

If you see larger bubbles surfacing after 15 minutes then should do a hydrocarbon (HC) dye test to test for potential head gasket leak.

Let engine cold down and top off coolant reserve tank.

Start monitor for coolant lost

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A coolant flush is require every 2 years or 24,000 miles.

I recommend the thermostat that has a relief pop-let to reduce the change of burst radiator and coolant hoses.

Make sure you get a new thermostat gasket,black RTV and fresh coolant for the job.

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This is typical of imports to cool the motor down when the car is not moving,as no cool air is entering the engine bay

Drain coolant from the cooling system. White plastic drain plug in bottom of radiator.

take off bottom rad. hose and top rad hose.

All wrenches and sockets are either 10 or 12 mm. Remove air shroud from around radiator and fan.
Sometimes its easier to remove fan too.

If its an automatic, remove 2 rubber hoses at bottom of rad.

remove 4 bolts top and bottom that hold rad. in place.

reverse order of parts. Fill with coolant and check for leaks.

That is the basics of it.
Bill