Team-BHP - Matiz - SG 99 - Overheating problem

I own a matiz SG 1999 model. It has done around 59000 kms and i am facing a problem in it for the past 2 months.

I travel around 35 kms to office everyday. In the morning car runs fine but while coming back, once the car has done around 20-25 kms it starts overheating when being driven at slow speed of its idle. This generally happens when there is hot weather (car stands out throughout the day). I got it checked at the service centre and they flushed the radiator, cleaned it and put an extra solution along with coolant. After that car ran well for some time (the weather also cooled off cuz of rains). Now that the heat is back the car is giving same problem. in the morning car doesnt give any troble at all.

One thing that i noticed is that Once i switch on the A/C the temperature gauge returns to normal in few minutes.
Is it happening because the the radiator fan which kicks off once we switch on the AC is not kicking witout turning on the AC ?
some problem in thermostat ?

Please help ...........

Also yesterday, when i was stuck in trafffic jam and i switched on the AC to bring the temp down, the horn stopped working (very very low sound coming, u have to concentrate to listen) after few minutes and only when i drove the car for 5 mins after getting out of jam it started working again. does the battery needs to be changed ? i changed the battery in 2004 may, so more than 3 yrs now.

Please help in both the issues.......thanks again guys :)

Quote:

Originally Posted by deeps79 (Post 534373)

Had exactly the same problem with my son's matiz. Thanks to MuraliSK who pointed me to Santosh of Banglore motor works, Adugodi. He diagnosed the problem - faulty temp sensor. changed it and all OK now. he is very professional and upright person.
Since i had also downloaded all the pdf files on matiz systems, thanks to HV kumar, i also knew a thing or two about the cooling system and the diagnostic test of a faulty temp sensor is this:- When engine over heats, Switch on ac and see if the temp comes down to normal it is temp sensor fault.The fan runs in two modes: without ac, it is temp sensor dependent and comes on and off. with ac on, it runs at high speed all the time. thus swithing on the ac drops the temp in a faulty temp sensor.
Thanks team BHP:)

The Matiz has 2 relays - the low speed fan and high speed fan relays. The high speed fan switches on when temperature goes beyond a point. I think your high-speed fan relay is not working, which is why the engine cools down when you switch on AC - because when AC runs, the fans run a high speed anyway. I have had this problem before and after changing the high-speed relay, the problem was sorted out. It is also possible that since your connectors have carbon/ rust in them, the relay is unable to establish electrical contact from time to time, which means high-speed runs sometimes also. You can easily detect that the high-speed is not running if you run the car in idle for some time, open up the bonnet and watch the fan running. When the temperature mounts, if the high-speed fan does not come on, you know the relay is defective. Interchange the relay with any other relay to recheck.