Carina E 1,8 Cooling Problem?

[jan42]

Can anyone help diagnose a problem with my daughter's Carina E? The engine revs on tickover sometimes increase, even when it has warmed up. I noticed this was associated with the temperature gauge dropping, indicating either a fault with the gauge/sensor or a genuine reduction in temperature while driving. Have taken it to Toyota who read the fault codes and said it needed a new oxygen sensor. This has now been replaced (at great expense since it is the lean burn engine)but the fault is still there. I have cleaned up both the temperature sender unit and the engine temperature sensor with no effect. Could it be that the thermostat is stuck open, preventing the engine from warming up fully and fooling the ecu into operating in warm up mode, increasing the tickover revs? Any help appreciated.

Thanks

Wayne

[Richard KM]

Can anyone help diagnose a problem with my daughter's Carina E? The engine revs on tickover sometimes increase, even when it has warmed up. I noticed this was associated with the temperature gauge dropping, indicating either a fault with the gauge/sensor or a genuine reduction in temperature while driving. Have taken it to Toyota who read the fault codes and said it needed a new oxygen sensor. This has now been replaced (at great expense since it is the lean burn engine)but the fault is still there. I have cleaned up both the temperature sender unit and the engine temperature sensor with no effect. Could it be that the thermostat is stuck open, preventing the engine from warming up fully and fooling the ecu into operating in warm up mode, increasing the tickover revs? Any help appreciated.

Thanks

Wayne

That's what it sounds like to me being an auto electrician. Did Toyota know about the temp decreasing when driving? You'd think they should have replaced the thermostat if they knew that, but then again, some guys just look at the codes, believe what they see and just replace those things, not testing much, missing the big picture.

[Jamesbelfast]

If you can get your hands on a multimeter measure the resistance in ohms of the coolant temp sensor when cold and then when hot. If there is little or no change then suspect its faulty. The engine coolant temp sensor has the biggest influence on fuel mix and if over-fueling it will throw up an oxygen sensor fault. This is a common mistake made by some mechanics. In other words if a fault shows the oxygen sensor it reading outside its normal parameters they assume the oxygen sensor is at fault when in fact the fault lies elsewhere.

It may just save you the expense of changing the thermostat.:)

[jan42]

Thanks guys, will try to test the engine coolant sensor before I change the stat. However, I noticed today that the top and bottom radiator hoses are warming up at the same rate when starting from cold, so I am inclined to suspect the thermostat.

If you can get your hands on a multimeter measure the resistance in ohms of the coolant temp sensor when cold and then when hot. If there is little or no change then suspect its faulty. The engine coolant temp sensor has the biggest influence on fuel mix and if over-fueling it will throw up an oxygen sensor fault. This is a common mistake made by some mechanics. In other words if a fault shows the oxygen sensor it reading outside its normal parameters they assume the oxygen sensor is at fault when in fact the fault lies elsewhere.

It may just save you the expense of changing the thermostat.:)