Thermostat Problem?

[JERN]

Hi all

I noiced a problem with my temp gadge the other night on the way home from work. The engine had come to normal temp and driving at 70 the needle on the temp gadge suddenly shot down to just above the lower marking, it stayed there till i got home, the car drove fine.

I checked the coolent level the next morning, which was fine and pressure was relesed from the expantion tank, so no leaks. I drove the car back to work and the same thing happend, this time the engine never came to normal temp it rose a llitle but stayed below where it usaly would.

Does this sound like my thermostat is broke? Letting in coolent from the radiator at the wrong time?

By the way its the standard thermostat and not the PRT which i've been meaning to get, but was wanting a new radiator at the same time.

Any advice or checks i can do to find whats at fault?

[Adam]

I'd guess at one of the sensors that attaches to the L-shaped piece that is attached to the front of the block. Best bet is to get it onto a diagnostic machine and have them check those sensors.

[Richard]

Like adam said it could be the sensor on the water outlet elbow I think the one for the gauge reading is the blue connector. Or the other possible fault is that the thermostat has failed in an open position meaning that you have constant water flowing around at all times.

[soberphil]

I reckon it's most likely a sensor or the gauge.

If the thermostat was constantly open I think you'd still get up to normal operating temperature on a long enough run - it would just take a while.

Also that wouldn't explain the sudden drop while you were driving (and presumably the 'stat was already open).

I might be wrong about this, but I don't think the sensor on the coolant outlet elbow at the front of the engine provides the gauge with a signal, I think that one is for the engine management and there is a separate sensor for the gauge elsewhere. Like I said - I'm not 100% on that off the top of my head - I'll check when I get chance.

[Richard]

There are 2 sensors on the coolant outlet elbow a blue sensor and a brown sensor, the brown sensor is used for engine management (also operates the fans)

[JERN]

Cheers guys,

Am pritty sure its not the thermostat or brown sensor at fault, i left the engine running last night and the fan kicked in when the temp needle was only at 1/4.

Am i correct in thinking that its most lightly the blue sensor at fault and not the gauge itself?

Anyone know if the blue sensor is the same on all k-series engines?