I have a 2003 lexus IS200 and it is overheating. The thermostat works fine and fans do go on. The problem is when I switch of the engine, the hot water goes into the coolant bottle and end up spraying out of the coolant bottle. What could be the problem?

lost of possibilities, but without looking at it I would suspect the thermostat is stuck closed. if this is true it would only overheat when the vehicle is hot. Thermostat would require replacement.

Yes, it is possible to install a thermostat backwards, though unlikely. If the thermostat isn't opening properly, the hot engine coolant won't be flowing over the cooling fan switch and give you high temps. I would first determine if the thermostat was opening at all, and if it is, is it opening at the proper temp. I have had many new thermostats that, while new, didn't work correctly. To check the cooling fan motor, turn on the AC(if equipped) and the fan should engage. If no AC, disconnect the cooling fan switch, and the fan should engage. Check for power and ground at the fan motor. If you have both power and ground, the fan motor is faulty

May be its low on coolant or radiator hoses clogged or its thermostat issue,its remaining closed or it can be issue with coolant leaking from somewhere.Or cooling fan not running when when engine gets warm.
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There are many other possibilities causing these issues.:----
To troubleshoot the issue yourself,i provide you few very helpful links with solutions:-----
Click the link below:----

Dodge Dakota stalls, stumbles at idle. Has low fuel flow and runs hot?

http://schematicsdiagram.blogspot.in/2012/03/dodge-dakota-stallsstumbles-at-idlehas.html

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1991 Toyota Trecel: Engine Starts fine but dies when gets Warm?

http://whatisbyme.blogspot.in/2012/05/1991-toyota-trecel-engine-starts-fine.html

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1995 Lexus LS400: Running Hot?

http://whatisbyme.blogspot.in/2012/05/1995-lexus-ls400-running-hot.html

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Multiple problems on car: Car runs hot, A/C blows hot and car starts surging?
http://schematicsdiagram.blogspot.in/2012/04/multiple-problems-on-car-car-runs-hotac.html


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There are many possibilities for car overheating.

Faulty thermostat clogged radiator/plugged radiator, radiator hose worn out. Coolant running low. Low coolant pressure. Faulty temperate sensor.

I suggest you to go through the troubleshooting details mentioned in the link below:-----

All types of car overheating problems and troubleshooting?

http://technoanswers.blogspot.com/2011/11/all-types-of-car-overheating-problems.html

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These will help.

Thanks.

1992 ls400 engine light was on replaced thermostat now lights off......fans dont work anymore,last time it worked was about 3 weeks ago now having overheating probloms

Your fan clutch could be going out...iin other words, it may be turning, appearing to be fine, but not fast enough therefor, not cooliing the engine enough.

CHECK FOR LOW COOLANT LEVEL AND REPLACE THERMOSTAT AND THE RADIATOR PRESSURE CAP.IF CAR OVERHEATING AND COOLING FAN NOT WORKING.CHECK COOLANT FAN FUSE AND RELAY.IF BOTH OKAY,HOT WIRE COOLANT FAN,IF FAN WORKS, PROBLEM COULD BE FAULTY COOLANT TEMPERATURE SENSOR,OR FAULTY PCM, IF COOLING FAN DONT WORK WHEN YOU HOT WIRE FAN.THE COOLING FAN ASSEMBLY NEED REPLACING.

Sounds like you have coolant leak if you are loosing coolant or a bad thermostat. I would replace the thermostat, they run about $10. The other fan is an aux fan and will only run when the a/c unit is on.

You say it's overheating, more info needed such as:
Is the engine temp gauge showing that it's overheating?
Is it actually 'boiling over' and losing coolant?
If it's running hot, but not losing coolant, check to see it the cooling fan is operating when the engine temp rises. You may have a bad cooling fan switch that is not signaling the fan to go on to lower the engine temp.
It could be a stuck (closed) thermostat that is preventing proper circulation of coolant after the car reaches operating temp.

Try blowing the radiator fins out (from the inside) with compressed air--bugs and other debris can clog the air flow. Do the radiator fan(s) run when hot? If not, check for blown fuse, seized fan motor(s), bad relay, or bad engine thermal sensor. Is it losing coolant water from somewhere?

check the basic, from fuse and relay engine cooling . have the fan check making sure the fans motor is good, does the fans come on at all when the engine has been running for while, if not it can be the switch, i would go ahead and replace them both thermostats and thermostats switch if you haven't done it. Thermostat switch has to be good, which it turn on and off the cooling fan. Thermostat (work like a valve) has to also operate properly other wise the fluid will continue to flow hot or not flow at all. thermostats will cost 7-8 bucks and the switch cost 47-50 bucks.