Temp gauge reads hot when cold

check that the wire to the temp sender unit has not fallen off and is shorting out on the head/block. The power comes from the ignition switch through the gauge down to the sender unit and because the sender is a temperature controlled resistance unit the voltage is very low and so the gauge reads cold . as the temperature heats up , the resistance is decreased and so the voltage is increased though the gauge and the needle reads higher.. Hench if the gauge goes directly to hot on start up the wire is shorting out or the sender unit is faulty.

check the that wire to the temp sender unit is not shorting out as it will read hot if it is remove the wire and if the gauge goes back to cold then replace the sender unit.

Not exactly.
The check gauge warning light is on because the temp gauge is reading hot.
Does the temp gauge read hot as soon as you turn the key switch on, or not until the engine as run for a few minutes ?
If it reads hot without the engine being started, there may be a short in the wiring or the sensor may have failed.

Check that the wire to the temp sender unit is not shorting out before the sensor As water temp rise so the resistance in the sender unit decreases and the current increases so a short would indicate hot water. REmove the wire and see it any thing happens and if it stays cool then, Replace the sender unit

Well, "Or What" would be the correct answer based on the choices given. Please read this article about fuses: Where's The Fuse?

You most likely have a problem with the Coolant Temperature Sensor. There are a couple of temp sensors. The one with the single green wire is the one for the gauge. If you disconnect the wire from the sensor, the gauge should read COLD. If you take a paper clip or small screwdriver and ground the green wire, the gauge should read HOT. If this works, then replace the sending unit. If the gauge stays COLD even when the wire is grounded, Then you need to check for an open circuit in the green wire between the sending unit (Sensor) and the insrument cluster. If the gauge reads HOT even with the sending unit unplugged, then check the green wire for a short to ground between the instrument cluster and the sending unit. If there is no problem with the wire - Not open or grounded, then the gauge itself is bad.

Hi there,

Firstly - DO NOT run engine, when guage reads hot, as this will cause costly damage to head gasket & alloy engine head.

The fact that guage takes 1min to read HOT, would confirm the guage IS working properly.

So, other components which are likely to cause hot readings (in this order) are:

- lack of coolant (or leakage somewhere): is there sufficient green coolant at the correct level? Top up mixture to correct level. Repair any leaks.

- collapsed radiator hose: when engine is cold, start engine, then quickly watch both upper & lower radiator hoses to see if either begins to flex inwards (collapse). Replace if either hose is collapsed.

- bad/incorrect thermostat rating : when replacing thermostats, you must ensure it is of the SAME temp rating (they all differ).

- Incorrect Temp sensor rating: the ratings of this sensor must be within manufacturer's spec's.

- bad waterpump: the engine relies on the waterpump to distribute the coolant throughout the entire system. If waterpump is faulty, coolant will not flow quick enough, causing overheating.

If you still believe all of the above components are OK, then have your cooling system "pressure tested". This test should be done, before looking further at other electrical components.

Cheers,

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There should be one around the same area as the one you tried that only has one wire. Replace this, it's just a thermometer.

Switch ig. on, ground the sender unit wire for about 3 seconds see if the temp. gauge moves, if so change sender unit, if not then it is a faulty gauge reader.

make sure the antifreeze is full. if so, replace thermostat and refill