Temperature pressure sensor

Tiny
JUSTINTIME89
  • MEMBER
  • 1999 OLDSMOBILE BRAVADA
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
Could my car be over heating because my temperature pressure sensor is bad? And should I also change the thermostat at the same time?
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Tuesday, October 4th, 2016 AT 3:53 PM

7 Replies

Tiny
CARADIODOC
  • EXPERT
A temperature sensor tells the Engine Computer what the coolant temperature is. It does not cause overheating problems; it just reports them. The exception is when you have an electric radiator fan. Then the computer uses the sensor's readings to know when to turn the fan on.

You need to include a lot more detail or observations. Does the overheating occur at highway speed when no fan is needed? Only at low speeds when there is little natural air flow through the radiator? Are you losing coolant? Dd this start suddenly or come on gradually? What is the symptom that tells you the engine is overheating?

Thermostats very rarely cause overheating. When they stick, they usually stick open which causes a failure of the engine to reach normal operating temperature.
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Tuesday, October 4th, 2016 AT 10:32 PM
Tiny
JUSTINTIME89
  • MEMBER
It really starts to over heats when I am sitting. But once it warms up it over heats then the meter shoots back to cold?
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Wednesday, October 5th, 2016 AT 12:27 PM
Tiny
SATURNTECH9
  • EXPERT
Sounds more like the radiator fan clutch is not working correctly.
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Wednesday, October 5th, 2016 AT 12:46 PM
Tiny
JUSTINTIME89
  • MEMBER
But the fan is on.
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Wednesday, October 5th, 2016 AT 12:57 PM
Tiny
JUSTINTIME89
  • MEMBER
And the oil pressure goes up and down.
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Wednesday, October 5th, 2016 AT 1:00 PM
Tiny
SATURNTECH9
  • EXPERT
Is the fan blowing a lot of air? I mean a lot of air especially when it is up to operating temperature.
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Wednesday, October 5th, 2016 AT 1:02 PM
Tiny
CARADIODOC
  • EXPERT
You're listing symptoms that I can't tell for sure if they're related or not, so I think the best place to start is by finding a scanner, or a mechanic with one, to view live data and see exactly what the Engine Computer is seeing. If the computer is seeing normal operating temperatures, but they're varying up and down at first, particularly for the first ten minutes after starting the engine, you may benefit from adding a tiny bypass hole to the thermostat.

Most import engines have a thermostat with a very small bleed hole in them. Domestic engines typically don't. I replaced the thermostat in my '88 Grand Caravan many years ago with one that didn't have the bleed hole. The temperature gauge worked fine for many years after that, but one day I noticed the coolant temperature came up really fast, went too high, then suddenly dropped to too cold, then repeated. That cycle repeated four or five times before it stabilized and read normally.

What happened was the temperature sensor for the dash gauge was some distance away from the thermostat. High temperature would show up at the sending unit and be reported as overheating first, then the high temperature would slowly migrate to the thermostat causing it to open. Once it opened, the cold coolant from the radiator would rush in and cause the gauge to go down and the thermostat to close.

The purpose of the bleed hole is to allow the hot coolant to flow to the thermostat right away. I drilled a 1/16" hole in mine and never saw that problem again in over 150,000 miles.

During the '90s, most cars used two separate coolant temperature sensors. The single-wire sensor was for the dash gauge and the two-wire sensor was for the Engine Computer. If the scanner shows coolant temperature is varying wildly like the dash gauge shows, consider adding that bleed hole. If the temperature is holding steady, we may have an instrument cluster problem and the oil gauge is providing another clue.

Coolant temperature sensors have an extremely low failure rate, so look for other causes first. Also, dash gauges are notoriously inaccurate. They are best used for the driver to observe when something is out-of-the-ordinary, never for exact temperature.
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Thursday, October 6th, 2016 AT 3:25 PM

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