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How to determine if the thermostat is stuck? - Cars & Trucks

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Stuck thermostat can be stuck open (which means engine never gets warm enough, which means heater blows cold and gas milage suffers and maybe check engine lite comes on) or can be stuck closed (which results in overheating). Newer cars have two temperature sensors, one which controls a dashboard display, and another which tells the computer how warm the engine is and the computer adjusts fuel mix. On most cars, it is simple to remove the thermostat and replace it. Once removed, you can inspect it using finger pressure to try to make it open. If at room temperature it is already stuck open, replace it. If it is closed, you can put it in a pan of water (not one you ever use for cooking!) and heat it to 180-195 degrees to see if it opens. BEWARE - some cheap parts store replacement units are of poor quality. As cheap as this part is, use the best you can buy - maybe even from the dealer. Good luck.

Posted on May 17, 2014

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2004 trailblazer code po128

P0128 OBD-II Trouble Code
Technical DescriptionCoolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

What does that mean?This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.

CausesA code P0128 may mean that one or more of the following has happened:

Low engine coolant level .
Leaking or stuck open thermostat .
Faulty cooling fan (running too much) .
Faulty coolant temperature (ECT) sensor.
Faulty intake air temperature (IAT) sensor .Here's a link on replacing your thermostat.

Feb 06, 2013 | 2004 Chevrolet TrailBlazer

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Tucson V6 2004 - cause of high tempreture in engine

The simple answer to your question is that the engine cooling system is malfunctioning. The sytem must be properly diagnosed to determine the actual cause. It could be anything from a thermostat that is stuck closed or a cooling fan circuit malfunction, or even a water pump that is coming apart internally.

May 20, 2012 | 2005 Hyundai Tucson

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How can you tell if the thermostat is stuck and is it possible for the engine to be rebuilt without getting a single smudge in the dust piled on the engine?

Ill answer your last question first. If an engine is rebuilt completely, part of the job involves cleaning the parts. Therefore there should be little or no road dirt, grease deposits etc anywhere. In most cases, even if not properly cleaned, there would not be any accumulations at parting lines between parts and new gaskets should be evident, installed between those parts such as intake or cylinder heads. A complete rebuild is very expensive and requires that the engine be completely removed from the vehicle. determine if a thermostat is stuck, you'd need to remove it and actually look at it. If it's stuck open you can see that. To determine if it's stuck closed, you'd need to boil it and observe what temp it opens, or if it opens. Generally though, since a thermostat rarely costs more than a few dollars, it'[s easier just to replace it if you even think it's bad. You can alw sometimes get an idea about the condition o fthe thermostat by comparing the temp of the lower and upper hoses but if the radiator is internally obstructed it will give you a false diagnosis.

Jul 18, 2011 | 1998 Chevrolet Monte Carlo

2 Answers

I have a 2005 gmc jimmy, the engine light is on and i hooked up my code reader and it says Coolant Temp Below Thermostat Regulating Temp. What does this mean and how do i fix it?

your thermostat is designed to open at a specific temp, for example a 195 thermostat is supposed to start opening at 195 but will not fully open until it reached about 210. Your ECM has determined that your thermostat is not 'closed', but is hung open, not allowing the engine to reach a temp that the computer is set to see. So the thermostat is either malfunctioning, or your temperature sender unit is reporting the wrong thing to the ECU. Probably a good time to replace the thermostat, if the condition persists, replace the sender unit-both items together will cost less than $30 total.

Apr 18, 2011 | GMC Jimmy Cars & Trucks

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No heat....radiator is full

No heat? More than likely, it's a thermostat problem. If it is stuck in the open position, your coolant will flow out to the radiator to be cooled and not held back in the engine to get hot. I would recommend taking your vehicle to a mechanic and have them check it out. They should be able to determine quickly why you're not getting proper heat.

Feb 26, 2011 | 1990 Lincoln Continental

2 Answers question to you is why would a 1997 subaru outback legacy overheat if the fans are working?

This can be a leaking cylinder head gasket (common on this Boxer engine).

Dec 27, 2010 | 1997 Subaru Legacy

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My 2002 xterra has started running hot..code po 217 came on..after gas cap was put on wrong..cleared code put gas cap on right then fine for 2 weeks..when idleing heat gauge rises soon as i rev...

p0217 is coolant over temperature. the fan clutch may be slipping or the thermostat is bad. changing the thermostat would probably be the easiest and most inexpensive fix to determine the problem.

May 09, 2010 | 2003 Nissan Xterra

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The engine light is comming on. Took it to Autozone - giving a code "P0126 - Coolant thermostat condition; Low operating temprature, Probable cause - Low coolant level; Open or short circuit condition; or...

The "probable cause" is the "thermostat" is stuck open, not allowing the engine to reach operating temp (190-195f) . As for the sensors, obviously its working, but if its corroded, its leaking and needs to be replaced. Better hope the plug is ok or you will need to replace that also. Replace the thermostat. Stay away from autozone.

Jan 23, 2010 | 2004 Mazda MPV

3 Answers

Engine not getting hot check engine light is always on 2002 grand prix. Had intake manifold gaskets replaced 1 month ago

check or change the thermostat it could be stuck open thats why its all ways running cold

Oct 30, 2009 | 2003 Pontiac Grand Am

1 Answer

2005 dodge caravan need to know symptoms for faulty thermostat

There are two primary symptoms of a faulty thermostat (assuming you mean the coolant thermostat in the engine not the A/C Heater Thermostat).  The thermostat can fail in basically two ways:
1)  Stuck open - Engine runs colder, heater takes forever to heat up. 2)  Stuck closed - Engine runs very hot, then will suddenly drop in temperature, then run very hot again.  Or engine overheats constantly.  When the engine is hot, feel the upper radiator hose.  If it is not hot, you can bet the thermostat is stuck closed.  If it is hot, the thermostat may not be stuck close, but not opening at the proper temperature.
Stuck open is annoying, but not dangerous.  Stuck close is dangerous and can cause overheating-related damage to your engine.
If you are handy, you can replace it yourself.  Otherwise it is an easy job for a mechanic.

Jan 24, 2009 | 2005 Dodge Caravan

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