Jazz overheating warning lamp

[Cameron]

Greetings everyone!
My 2003 Jazz 1.3 ldsi auto 70k miles, shows the temp warning lt, first as a flash then solidly. The engine appears to be at normal working temp (by touch) The hot air through the blower is normal. The radiator is cool to the touch, and rad cap can be removed without scalding injuries!
My immediate diagnosis was that the thermostat had failed closed. Ive since swopped that out for a non genuine item (without the jiggle pin! I may revisit that and modify it)
Ive back flushed the radiator and ordered a temp sender unit.
Anyone had similar issues or any ideas?
Thanks in anticipation.
Cam

[olduser1]

Fit a honda stat, bin the other.
Any sign of coolant leaks inside the car it from heater core?
Any damage to rad?or hose clips etc
How long since coolant change ? If unknown use Honda coolant.

[Cameron]

Thanks for the responce. Levels are all good with no leaks. Hoses and clips in good condition. Radiator as you would expect from 22 year old item, is tired but still solid.

[embee]

Sorry for the late.
The "engine side " of the coolant system must always be completely full at the radiator cap. The crucial aspect is that the rad cap valves and the recovery hose to the "make up" bottle must be good with no leaks. When it heats up the coolant expands and is pushed out through the high pressure valve in the cap into the bottle.
 The small hose from the rad cap recess into the bottle must go down to near the bottom in order that coolant is drawn back into the rad when it all cools down.  The cap has a low pressure valve to allow reverse flow back into the rad.
Any air leaks in the hose will result in the engine side gradually losing coolant. The rad should be completely full to the top when you remove the cap with it cold. I've seen cases where the hose inside the bottle has fallen/broken off.