My Nissan Sentra ccolant system keeps overheating. I have overhauled the motor, changed the radiator fan thermoswitch,flushed the radiator, fitted new radiator cap but the coolant keeps overheating. I am looking for advice towards a solution please.

I am assuming you flushed out the entire cooling system after you rebuilt the engine.
Did you examine the water pump? If that isn't working correctly it won't be moving the coolant around the engine fast enough to keep it cool.
Have you had the vehicle scanned with an OBD2 scanner? This will find out if it is a sensor that is causing the problem. If you have to pay for this service ask at 4 or 5 different places as prices can be VERY different.

Do the radiator fans work? Are the external cooling fins clean and unobstructed? Could the radiator flow be restricted? Do you have a head gasket that is leaking. Did you bleed out all of the air in the system? Is the radiator cap good?

flushing a cooling system is the same method as any other motor

do it without the thermostat fitted
or water pump opening

sacrifice an old radiator hose to adapt a garden hose fitting
for radiator flush

air in system fix
your thermostat housing has no air bleed valve
no top radiator cap

old school way
heater on full
run motor till thermostats fully open
burp radiator hoses
wait till water is running up into over flow bottle without bubble
replace cap
turn off heater
correct level in over flow bottle

why still over heating
you fitted everything i would have ... yet still overheat
possibles
leaking inlet manifold gaskets
hose clamps loose
cooling fans spinning too slow
thermostatic fan switch faulty
aluminum radiator is a big one
air ..fins bent or some water channels blocked

or possible head gasket leak

1. The radiator cap if working correctly it will release pressure in the system provided the cap you have is the correct pressure setting. If you are having a problem with pressure then replace the cap with a new radiator cap with the correct pressure setting. Do not use a cap with a pressure setting other than the original equipment pressure spec. So you do not go to the parts store and buy any radiator cap on the shelf that fits because they come with different pressure ratings and some of these will be totally unsuitable for your car.

2. If the pressure valve is stuck in the "old" cap the pressure release system will not work.

3. Overheating
Air pockets in the cooling system can definitely cause overheating and can retard coolant flow through the system. If you are draining the radiator to replace the coolant or replacing the radiator you need to follow the correct procedures for bleeding air out of the system for that particular engine after coolant refilling. Some engines have bleeder screws on the cooling system to assist in the air bleeding procedure and some don't.

There are various causes for overheating so don't assume it will necessarily be solved by bleeding any remaining air from the cooling system and replacing the radiator cap with one that works.

Other causes can be...........
1. Faulty cooling system thermostat. (Replace the Thermostat)
2. Faulty water pump, especially if the impellers have corroded away or have disintegrated in the case of those design genius water pumps with plastic impellers. (Replace the water pump)

3. Cooling fans not working and if so the cause needs to be tracked. Check that your fans are kicking in. If the engine is overheating the fans should be running because they will switch on when the coolant reaches a specific temp and well before the coolant gets excessively hot.

4. A partial blockage in the coolant passages inside the engine but not in the radiator if you have a new one. If the coolant is not changed at the required intervals(frequently the case with many owners) or is over diluted with water you can get a build up of debris. If products like stop leak have been used in the system this can create similar problems with partial blockages inside the engine coolant passages.

5. A compression leak into the cooling system.
If you have bled air from the system and have continuous air bubbles in the cooling system I would suspect a compression leak. In that event a basic leak down test will show if you have compression gasses leaking into the cooling system and from which cylinder(s). The spark plug is removed and compressed air is forced into the cylinder via the spark plug fitting and air bubbles will show up in the coolant of there is a leak into the cooling system.
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Have the problem with overheating addressed immediately. Running the engine with an overheat condition will cause expensive engine damage many times the cost of fixing the overheating issue.

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Some thing too check:
Make sure coolant level is up to line and clean (not dirty, do to clogged radiator, may need to be flushed or replaced).
Make sure air flow through the out side of radiator is clear (dirt, leaves, ect..) .
Make sure fan is working properly equip t (is not running too slow). Or Manual (belt driven) fan clutch is working properly, not loose or spinning too freely?
Check for broken or cracked fan blades itself.
Check radiator cap, (no gasket tears).
Could be thermostat going bad ?
Could be coolant temperature sensor/switch (from computer) going bad?
Check radiator hose(s) (too soft, may collapse)?
In some rare cases:
Timing could be off.
Could be water pump.
Could be blown head gasket(s).
Could have cracked head(s).
ECT..............Hope this was some help???

Check to see if the radiator fan switch if working properly.

have radiator system flushed at a radiator repair shop

then the water pump must be bad in it .Take the rad cap off and rev motor up if it goes down the the pump is working if it spays of look at the head gasket being damaged .Check and make sure spark plugs are not wet either if one is soaked signs of a leaky head gasket

it sounds like a water pump not circulating antifreeze properly

hi. was just looking at your problem of (sentra) overheating and actually, i am a mechanic for nissan and have changed many head gaskets for this particular vehicle equipped with 1.8 liter motor and found that they are notorious for this problem of faulty head gasket's.Unless you did't properly bleed the system,which i doubt because you seem mechanically inclined since you already changed every other part of the system,i would't doubt that this is the problem.Anyway, by the time you read this, you have probably already found this out..Just thought i would let you know this info.Good luck!...by the way,if you haven't already changed you cam and crank sensors,do that too,before you get stuck and get the part's at the dealer!!!!-they are redesigned from the old one's!!just some advise to try to help you out!!! John from N.Y.