Question about 2001 Nissan Sentra

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Heater not working with radiator cap

Heater does not work with the radiator cap on and if its on and you hit the Highway or about 2000+ rpm you heater may work and car temp goes to normal.. Also if the heater is not working for more than 15-20 mins the car temp gets Hot and Hotter. Also there is water sound if the heater is working Or in other words as long as the water sounds in heater core heat is ON and if no sound= no heat..?????? seems like no one had this problem....EVER pls help this problem is really driving me crazy.. Radiator changed pump changed. Please put your expertise advise.. all responses are appreciated..

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There is probably an air pocket in the system. if it has a bleeder valve , bleed the system while running or get a burp funnel

Posted on Jan 06, 2013

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  • zesty Jan 06, 2013

    Thanks for your comment,, But the system has been bled 10-11 times ,, everytime if the engine is on with radiator cap off and funnel ON .. to purge the air out... after 10 -15 min ,, everything seems to be and heater starts working.. as you close the radiator cap back and close it,,, 5-10 min after again no heat and car temp sometimes shoot up... unless car hit the highway...where heater makes sound and heater works and temp goes to normal..???? isnt weired ????

  • madmaxx Jan 06, 2013

    possibly a week water pump not circulating properly

  • madmaxx Jan 06, 2013

    sorry i just read that u replaced the pump, my next thought is to check the valve on the hose going to your heater core. it may be stuck, follow the hoses from the fire wall you should find it

  • zesty Jan 07, 2013

    Well your time and input is truly appreciated,, this is the first time , i am here about valve and firwall.. can you please guide me where exactly to look for,, you meant heater core inlet or engine outlet to heater core inlet. Also just to give you an update,,why i would prefer to find out myself the problem and not going to pro mechanic after spending 100s of $.. Today i went to pepboys and two mechanic had different views on the same problem. One says keep changing thermostat and other is say sure shot its headgasket failure.. this type of experiment i want to avoid and would like to share experience and expertise from others like you...I would appreciate if you help me locate this valve may be that is the issue..its nissan sentra 2001 1.8L..hope this where the problem exist..

  • madmaxx Jan 08, 2013

    i just re read your first complaint and the heater core may be clogged. disconnect both hoses going to fire wall and back flush it with a garden hose. back n forth between hoses. i think the gargling noise is water squeezing past a blockage. give that a shot

  • zesty Jan 08, 2013

    thats what i thought in the begining until i did the procedure as you have mentioned. I ran the water both way to the heater core , nothing was clogged and water ran smoothly ...what else you might think of...or anybody PLEASE...


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Posted on Jan 02, 2017

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SOURCE: 2000 Xterra intermentantly overheats

sounds more like the thermostat may be failing. generally a water pump starts leaking out of the "weep" hole in the casting before it quits. just look at the front of the water pump for a greenish streak or an obvious leak.
if you also suspect you heater core may be getting plugged now would be a good time to back flush it to get rid of some of the gunk.

Posted on Oct 22, 2009

  • 2359 Answers

SOURCE: Nissan Altima running hot

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

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


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

This test will kill two birds with one stone.




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


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


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.

Please post more information by clicking the comment link on the top right corner.

DON'T FORGET to RATE ME if my tip is helpful to you!

Posted on Dec 05, 2009

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1 Answer

My 2004 3400 closed system ,runs hot in town unless heater is on. driving up a mountain pass it gets very hot.on a flat highway runs normal. new t state,resivior cap, both fans work no leaks or smell

Radiator fan motor or radiator fan thermostat defective/

Also there is a relay that operates the fan motor

In town not enough air passing through radiator allowing it to over temp.. With heater fan running acts like cooling fan keeping engine cool

Highway driving ample air passing through radiator without fan.

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Hope this helps?





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I have a 2000 Lincoln ls v6 I replaced the upper radiator hose with thermostat housing assembly and now my heater doesn't work. What could be the problem

Hi, you probably have air in the system. Park on an incline, turn the heater on, open the radiator cap, start the engine, and let it run until the thermostat opens. Keep the radiator full and when the level stops gong down your heater should be working again.

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Heater blows cold air when the truck is idling or in stop and go traffice

a question to an answer: is your truck has any heat when you rev it 2000 rpm, or above?
have you check your coolant level? if level is low you have a small coolant leak, a water pump may be at fault, and causing air pockets in your heater core, check for leaks your self, dealer wont tell you if vehicle still under warranty.
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Feb 03, 2011 | 2006 Nissan Frontier

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We have a 2000 frod expedition. We started to expirience that the heater would work then blow cold air. we replaced the thermostate then the engine would overheat. right after starting it would blow hot...

Try bleeding the air out of the system again. This truck has the radiator cap located lower than the heater core & upper hose and easily traps air pockets in it. It also helps to park on a slight incline and have a helper bring the rpm's up while "burping" the system.

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Heater blows cold when motor is idleing, Heater was flushed and water level is ok. workes good at highway speed

You have a partially blocked heater core. This is not a repair for the average DIYer. Any radiator shop can repair it by rodding, or just buy a new one - they're less than $100 but a real job to get out. I'd take it to a professional or if you're game, pick up Chiltons for 2000 Taurus and give it a go.

Jan 31, 2010 | 2000 Ford Taurus

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Car overheating, blows cold air out vents, changed engine,radiator,thermostat,water pump, and heater core

A couple of things to check because as you describe your symptoms you actually have 2 problems

1. No heat from vents.

Sounds like the heater water flow valve cable is kinked disconnected or the valve itself is stuck You will need to follow your heater core water supply lines to find the valve usually to the right of the center console in the ducting area / large plastic housing for heater and AC internal coils. If the valve works then there is a possibility that the heater core water supply lines have been bypassed on the engine side of the firewall with a coupling due to a leaking heater core. And l;astly the heater core could just be clogged. (quite rare!!)

As for the overheating engine after all of the work you have done.. Perform this simple test.

1. remove radiator cap
2. have someone else start the car
3. watch for water coming out of the open radiator cap area DURING start...
4. have person in the car rev engine gently 2 or 3 times. No need to exceed 2000 RPM. If water rapidly flows out of the radiator during engine revs.. you have some major engine issues.
If it passes all of these checks then the only thing left is improper hose connections on the engine side of the firewall and or a hydraulic water lock in the block that should clear itself by starting and stopping the engine many times with the radiator cap off.

Jan 27, 2010 | 1997 Pontiac Grand Am

1 Answer


Concerning the heater problem.Sounds like you have an air pocket in the system.To remove the air pocket take off the radiator cap in the morning when the car is cold,fill radiator to top.Start the car.Turn on heater to high.Allow car to run until it gets to operating temperature.Now you will see the fluid in the radiator start to go down.This means the thermostat is opening.As fluid goes down fill radiator to top (with 50/50 antifreeze/water mix).You may have to wait a moment for it to continue to move down.Once it stops and the radiator fluid isnt going down,slowly bring up the rpm's (by either turning the throttle with your hand or have someone put their foot on the gas) to about 2000rpms and hold the rpm's there steady.As you hold the fluid will go down a little more.As it does fill to the top again and quickly put the radiator cap back on while the rpm's are steady at 2000.After the cap is correctly on release throttle.This should remove the air posket.

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Replace the thermostat
check and or have the water pump check
open radiator cap start cold engine add coolant
step on gas a bit about 2000rpm add more coolant hold the peddle close radiator cap

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