Hello Guys.
My B is nearly overheating . The temp is going to 3/4 all the time. The fans are working, I put a new Thermostat just in case. The temp goes down for a while but then up till 3/4 again. I know that my heater matrix has a leak because I can see some coolant trying to escape from the heater matrix, but it is a very small leak and I don´t need to top. I read over an italian forum that a broken heater matrix could cause boiling water and overheating . Anyone knows about that? Any recommendations?
Thank you!!

It might be that your cooling system generates pressure. Heater matrix can drip under pressure but not leak enough to lose a lot of coolant.
Obviously your coolant isn't flowing freely.
Try out your coolant hose firtst with cold engine and then while running the engine. Does it feel a lot harder when running? Does your coolant reserve tank gain pressure? If so, does your coolant filler cap release pressure properly?
Do you see bubbles coming from the tank when running the engine?
Coolant liquid looking clean or oily?
Might be a case of blown head gasket.

Ilkka, thanks for your reply.
Heater matrix drips under pressure, but just a little bit. The coolant hose gains pressure with temperature and it feels a lot harder. THe reserve tank gains a LOT of pressure, I thing the filler cap is working propertly (don´t know how to check it though). I don´t see bubbles coming from the tank when running and the coolant liquid looks very clean, not oily at all.
Any advice? I don´t know what else to check . Maybe the radiator is a bit clogged?

First guess would be a jammed thermostat, but since you have a new one it should be something else. Did you have the problem before you changed the thermostat?
Check it anyway: put your cabin heater to full+full blow and check if you are getting hot air. If not, then it might be just air in the system.

But still, since the high pressure, my best bet would be the coolant isn't flowing freely -> a clogged radiator or coolant hose. Worst case the head gasket or even the head.

Does it overheat also when driving on a open road or only in traffic?

Let a mechanic check it, the cooling system isn't that complex and it's usually easy to repair. Radiators are quite cheap and easy to replace.

Yep, thermostat is working, I´m getting hot air inside the cabin. If I´m driving on an open road the temp is alright, stays just in the middle. The problem is in traffic, the gauge starts climbing till it reaches 3/4 and then fans kick in and gauge goes to the middle for a while and then starts climbing again. I had the problem before the thermostat´s change, but now I wan´t to solve it before summer comes.
Another problem I always had is PINGING or KNOCKING when temp reaches 1/2 or 3/4. I tried every quality of fuel but no difference made. I don´t know if this has anything to do with the temp problem...
I didn´t fix these problems before because I drive the barchetta only on weekends.

Hmm, since the cooling and thermostat work fine, only the fans turn on too late, now I'm thinking it might be the temperature sensor. That might also have those symptoms.
Do this: take of the temperature sensor plug.
The car ECU loses temp reading and turns on the fans.
Now see if the temp rises above 90'C or not. If it doesn't, then your cooling system is propably ok and the problem is fans kicking in too late (too high temp).
This case check temperature sensor wiring and possibly replace the sensor.

Btw., do you have air condition? One or two fans?

Check the pics attached. If you have air condition and thus two fans maybe your first fan isn't kicking in. Either the fan, connector, relay or air-con pressure switch is broken. The second shouldn't start before the temp reaches 100'C.

Hello Ilkka. You are being very helpful mate! THank you.
These are the news: I disconnected the temp sensor. Temp reaches 90, both fans working all time long, thermostat opens ok, temp stays at 1/2 . When temp sensor is plugged, the smallest fan kicks in at around 93. I have seen the sencond fan working only when I turn AC on, but temp doesn´t reach 100c easily.
I was thinking on replacing the temp sensor because of the pinging, but don´t know how to check if this sensor is broken or not.
Hope this info helps, I feel that with your advices I´m getting somewhere!! Cheers!!

So the good news is that your cooling system is propably ok.
To check the temp sensor you need a multimeter and a thermometer to get a reference temp.
Or, you can take a little water, put ice in it so you know it's 0'C and then boil some water to get a 100'C reference. And if you want, check your room/outside temperature take a third reference there.
Use the multimeter to get a readout from the sensor, an compare it to the chart in repair manual (for some reason this page is in dutch).
It read out quite close, ~1% tolerance.
If it's significantlly something else, replace the sensor. Also check the plug/wire for damages/wear.

Hi Draco another thing you could look at.....

I had trouble with overheating when I first got my car. Seems there is a coil type resistor mounted on the fan housing in between the fans. not sure what it's exact function is but it's held in place by 2 screws and is easy to remove.

My origional one was burnt out. since replacing it and flushing the cooling system overheating problems have been cured.

Hope this helps

Wayne

Good thinking. Low speed mode is fed through the resistor, so if it's broken then the fans kick in directly to high speed at 100'C. See the curve diagram. Also if the low speed fan fuse is burned the result is the same. So check both of them. See relay connection diagram.

Now I´m between those 2 things. The temp sensor or the resistor. Replacing the sensor is easy, I just need to buy the new one and "plug&play". At 1/2 the smallest fan kicks in for a few seconds, then stops. The gauge stays at 1/2 for a while and then starts climbing again and the fans kick in at around 95c, not at 1/2 any more. I have never seen the second one kicking in, except when AC is working...
Maybe I should try replacing the resistor first. Is there any way to know if the fan resistor is working propertly or broken?

Checking the resistor is easy if you have a multimeter. You don't even need to remove
If it breaks, it loses conductivity so R=∞ (you won't get any readout on any range)
If it's ok, you'll get some readout, I don't know what the value should be though.
However, if it's broken the low speed mode shouldn't work at all.
So when the fans kick in for the first time aroud 90'C, are they on lower speed than the second time? If not, then it's propably the resistor or low speed fuse.

I will check the resistor today. The fan kicks in at around 92C and it sounds very slow. I think second speed never engages. I have an Alfa 155 2.0 and the fan sounds much much "faster" than the B.

Ok guys, these are the news:
I replaced the fan resistor and the temp sensor. Tomorrow I will take the B for a spin and see what happens with temp (today is raining a lot
If the problem is fixed, I'll post a new thread explaining everything we did to fix it.

More News: I have been driving the B for a couple of days now. Temp stays in the middle now, so I think it is fixed. I don´t know for sure because outside temp now is 5°c in winter. It was overheating in summer when temp was around 30°.
Pinging is still there, so I´ll try to replace spark plugs first and then clean the injectors.
Will post more if any change.
Thank you everybody for the help!!