Coolant boiling in resevoir.

It can be faulty coolant temperature sensor.Its not sensing exact coolant heat temperature so its overheating then required level.

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Get the coolant pressure tested, its definitely leaking coolant. You will need to get the coolant running line.

Pressure test will help you to know from where exactly coolant/refrigerant is getting leaked.

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For complete step by step troubleshooting i suggest you to go through the help links mentioned below :----

Click the link below :-----

Coolant enters in transmission on Toyota Land cruiser?

http://schematicsdiagram.blogspot.com/2012/01/coolant-enters-in-transmission-on.html

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1991 Toyota Camry: Order Coolant Bypass Tube?

http://whatisbyme.blogspot.in/2012/05/1991-toyota-camry-order-coolant-bypass.html

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2002 Toyota Camry: Puff of Blue or White Smoke while Starting?

http://whatisbyme.blogspot.in/2012/05/2002-toyota-camry-puff-of-blue-or-white.html

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1994 Toyota Camry: Coolant Leak?

http://technoanswers.blogspot.in/2012/04/1994-toyota-camry-coolant-leak.html

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2006 Cadillac DTS: COOLANT LEAK AT DRIVER SIDE NEAR FIREWALL?

http://schematicsdiagram.blogspot.in/2012/04/2006-cadillac-dts-coolant-leak-at.html

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MAF, IAT, MAP and Coolant Level Sensor problem all together on Mazda MPV?

http://schematicsdiagram.blogspot.com/2011/12/maf-iat-map-and-coolant-level-sensor.html

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GMC Engine Coolant Temperature (ECT) Sensor Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-engine-coolant-temperature-ect.html

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Loosing Coolant?

http://whoisbyme.blogspot.in/2012/06/loosing-coolant.html

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Coolant temperature sensor dies again and again?

http://schematicsdiagram.blogspot.com/2012/01/coolant-temperature-sensor-dies-again.html

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2000 Daewoo Lanos: Where to Add Coolant?

http://repairhelpcenter.blogspot.in/2012/06/2000-daewoo-lanos-where-to-add-coolant.html

Blue Water Warning Light on Dash?

http://whatisbyme.blogspot.in/2012/07/blue-water-warning-light-on-dash.html

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Replacing Oldsmobile Engine coolant sensor?

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How to test Engine coolant temperature sensor?

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Replace Coolant Sensor Module on Oldsmobile?

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These details will help.

Thanks.

Engine overheat while driving could have low coolant level,faulty thermostat.faulty water pump.ignition timing off will cause overheating,faulty radiator pressure cap.faulty cooling fan.radiator core blocked or front grille restricted with debris like leaves bugs trash dirt. many things will cause engine overheat.