Question about 1991 Pontiac Bonneville

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Where is the thermostat located on a 91 Bonneville 3.8 liter engine? The engine overheats when stopped and the fans do not engage. I suspect the control thermostat but cannot locate it on the engine

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  • Pontiac Master
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THE CHEVY 3.8 A GOOD ENGINE BUT YOU CAN;T LET THEM OVER HEAT EVEN ONCE THE INTAKE MANIFOLD IS ALUMINUM AND TENDS TO WHORP CAUSING THE HEAD GASKETS TO LEAK IN TO THE CYLINDERS ANTIFREEZE YOUR T STAT IS LOCATED ON TOP OF ENGINE LOOK AT TOP HOSE ON RADITOR FOLLOW IT BACK TO THE OTHER HOSE CLAMP ON THE HOSE THATS WHERE IT IS ALTHOUGH YOU PROBELLY NEED A NEW RADITOR AND A COMPLETE FLUSH OF THE SYSTEM YOU MAY WANT TO THINK OF GETTING RID OF IT WHILE IT STILL IS RUNNING SORRY HOPE IM WRONG BUT YOUR T STAT IS NOT THE OLNY PROBLEM GOOD LUCK

Posted on Oct 12, 2010

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Overheating in 91 honda accord


Remove the thermostat and run the engine at idle until it starts to overheat. If it does then the radiator may have clogged veins and needs replacing.

Aug 31, 2012 | 1991 Honda Accord

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97 pontiac bonneville. The cooling fans are not working and the engine temperature climbs when stopped. Also, the coolant gauge is coming on as low but it is full.


if your fans are electric check fuses and relay if they are good replace your coolant temp sensor that is what is most likely wrong anyway cheap at auto zone they are normally located right by thermostat housing or in the side of the block it tells your cars ecu when to cut on fans.

if your fan is belt driven replace you fan clutch and problem solved


if this helps you could you leave me good feedback thanks

May 09, 2011 | 1997 Pontiac Bonneville

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My 95 bonneville is losing coolant and getting hot. Could it just be the thermostat?


more info would be needed to accurately assist you. the bonnevilles typically had a 3.8 liter engine that had a liquid cooled throttle body assembly. it was common for the gasket between the throttle boty and upper intake manifold to leak. this leak if left unattended for extended period of time could result in low coolant levels, therby causing it to overheat....any time any vehicle overheats..it is wise to replace the thermostat as it can fail as result of overheating....the throttle body is the first component on engine after the large rubber hose of the air filter housing attaches to the engine

hope this helps

Aug 03, 2010 | 1995 Pontiac Bonneville

2 Answers

I have a 91 Dodge Caravan LE 3.3 liter V6 engine, The long story on what problems I have had with this car is as follows. The first thing that happened was I had a fusable ling burn out on the van, this I...


For first check the coolant level.If its low then it must be made full.If its full then check out for any kind of coolant leak.If the coolant is low or getting leaked from somewhere then the car will overheat.So get the ac pressure test done.At any local car garage they do ac pressure test.Doing this test will let you know that there is coolant leak or not.If there is coolant leak then that leak is the cause of overheat.But if there is no coolant leak and coolant level is also full.Then ignore coolant cause for overheat.Then other cause may be the thermostat ,thermostat allows coolant to circulate when the engine is warmed up and should be closed when the engine is cold so that the car can warm up faster. It's a fairly inexpensive part that's replaced easily, but when it fails, your car can overheat, causing costly engine damage.
To check if thermostat is faulty try this procedure:--
Warm up the car but don't let it overheat--don't let the thermostat gauge go into the red.Turn off the engine.Open the hood.Find the upper radiator hose. It's black, is made of rubber and is about 2 inches in diameter, with metal clamps on either end. The upper hose goes into the top of the radiator.Locate the lower radiator hose. It looks similar to the upper hose except that it attaches to the bottom part of the radiator.Touch each hose very carefully (they can be extremely hot). If the temperature gauge is indicating that the engine is warmed up but one hose is hot and the other is cold, the thermostat is probably stuck closed, and the coolant isn't circulating through the radiator.the thermostat is faulty is the case. If the thermostat checks out ok then it can be faulty temp sensor.Its also called coolant temperature sensor. The coolant temperature sensor is a thermistor ( a resistor which varies the value of its voltage output in accordance with temperature changes. ). The change in the resistance values will directly affect the voltage signal from the water thermosensor. As the sensor temperature decreases, the resistance values will increase. As the sensor temperature increases, the resistance values will decrease.
The coolant temperature sensor lets the engine control computer know what the engine temperature is by gathering information from the engine coolant temperature.
There are several ways to know if the coolant temperature sensor is malfunctioning, if the sensor is bad it will trigger a trouble code and the check engine light in the dashboard will come on, you can retrieve the engine code and see if it is related to the coolant temperature sensor, even if the engine control computer doesn't store a trouble code, there is another way to suspect a bad coolant temperature sensor : If your vehicle starts using more fuel than usual, starts having trouble starting when the engine reaches normal operating temperature or you notice black smoke coming out from the exhaust tail pipe, it is very likely that these symptoms are related to a bad coolant temperature sensor. A thermostat that is stuck closed will cause the engine to overheat. To test if thermostat is stuck in the closed position, place the thermostat in boiling water. If the thermostat doesn’t open, than the thermostat is defective and needs to be replaced.
Check the Engine Coolant Fan
Since the cooling fan pushes air through the radiator to cool the coolant, a fan that’s not working properly will cause an overheat condition.
  1. Electric Fan – If the vehicle is equipped with an electric cooling fan, check to see if the fan is working properly. Most electric fans will only operate when the coolant temperature reaches a certain degree. In many vehicles when the air conditioner is turned on, the electric fan automatically turns on. The most common cause of an electric fan failure is the fan motor, a controller module or a relay.
  2. Engine Driven Fans – Some vehicle have cooling fan driven off the front of the engine. If the clutch (between the fan and the engine) is bad it may slip. If the clutch slips it may not allow enough rotation on the fan to be affective and the clutch needs to be replaced.
Thanks. Keep updated for any more query. You can rate this solution and show your appreciation.

Jul 21, 2010 | Dodge Caravan Cars & Trucks

1 Answer

Thermo valve broken, does this cause over heating?


if you mean "thermostat" valve .. then that can fail either open or closed . if it fails open then the engine will not reach normal operating temperatures .. if it fails closed then yes the engine will overheat .. another common failure is the radiator fan .. it only runs when the car is not moving .. as long as the car is moving then cooling air is available so the fan is not needed ... so if your car does not overheat when driven but overheats when stopped or idling then suspect the radiator fan or thermal switch (mounted on the radiator) .. that switch turns on the fan when the radiator gets so hot ... you can just listen for the fan when hot .. you should hear it .. .. if your car gets too hot while driving then suspect a bad thermostat or clogged radiator .. sometimes a bad water pump (broken implellers) will cause the trouble ..

Jun 10, 2010 | 1990 Acura Legend

1 Answer

Location of the Auxiliary fan switch


The auxillary fan is used for AC cooling purposes, and your vehicle under normal circumstances should not overheat regardless of the status of the auxillary fan.

That being said, the auxillary fan is controlled by the PCM based on AC switch position via a fan control relay in your fuse box under the hood. There is no fan switch for it, as it is turned on based on PCM observance of AC control switch position.



Some things to look at regarding your overheat condition:

When the vehicle begins overheating, what are the conditions of the radiator hoses? Are both firm, or only one and the other soft? Are both hot, or is one hot and the other only warm?

Both a failed waterpump and a failed shut thermostat will show a hot hose on one side and only a warm hose on the other side of the radiator.

A failed (stuck shut) thermostat will also result in one very firm hose (highly pressurized and nowhere to go with the thermostat shut) and one relatively soft hose.

You can take the radiator cap off (BEFORE it pressurizes) and watch the water level as the car runs. If the thermostat is opening and waterpump is pumping, you will see fluid flow once it gets to operating temperature.

Watch your engine fan and see if it is engaged or just spinning freely. When warm and the engine shut off, the fan clutch should be engaged making the fan more resistant to turn. If it spins freely, the clutch is failing.

Check the area around the radiator and between it and the condenser for obstructions to airflow.

Obviously check the condition of the coolant for heavy scale/sludge. The 3.0/3.5 engines are notorious for turning coolant into thick rusty puddy.

Hope this helps!

Sep 11, 2009 | 2001 Mitsubishi Montero

1 Answer

1998 Pontiac Bonneville overheat


no the computers only job is too turn on the fans. check for enough antifreeze check for leaks. these cars are known for leaks. if the water pump is broke internally it will overheat with in minutes, or if the thermostat is stuck it will overheat too.

Aug 04, 2009 | 1998 Pontiac Bonneville

3 Answers

90 subaru legacy overheats, wheres the thrmostat


When a car overheats it's rarely the thermostat. They just don't go bad that often. If it overheats when you idle a lot, it's the fan and with electric fans, it's almost always the fan motor. But to find the thermostat, follow the top radiator hose to the engine and there it is.

Aug 01, 2009 | 1990 Subaru Legacy

1 Answer

Over Heating


use a/c to engage cooling fans and keep engine cool til you locate the fan/circulation problem....
cooling fan temp switch is a likely suspect also the thermostat for general circulation problems .. be sure to flush and fill when servicing thermostat .. belts hoses water pump round out suspects here..... without any more info all i can tell you

Sep 05, 2008 | 1990 Nissan Pulsar

1 Answer

91 SL1 problem


the sensor is located at the rear side of cylinder head between transmission and engine under the thermostat hosing but make sure to have some one aply direct power to fan to se if fan still goos if not replace it, and the sensor all what you have to do to test it start the car unplug the sensor and if the fan come on then replace the sensor i will recomend to replace thermostat also and make sure is full of coolant

May 30, 2008 | 1999 Saturn SL

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