(T) Brava engine overheating - fan help!

Hi,

I have quite a large problem with my Brava 2001, 51-reg 1.2.

When driving normally, the car is showing perfect levels on the temperature gauge, at half way.

Whenever I get into traffic, however, the temperature reading on the dash gradually rises - it's been to just below the red level before I managed to get clear of the traffic.

Now, i've checked the relay and it works fine, as does the fan when it's shorted to earth. My dilemma is, what is the problem likely to be?

Any help will be greatly appreciated.

Thanks
Mark

Could be a number of things., is there enough coolant in? any signs of HG failiure? Mayo substance in oil, heater blowing cold etc. Is your thermostat opening. i had overheating problems a while back. found out it was a dodgy coolant temp sensor and a blocked radiator which i replaced. Could be something as simple as an airlock though.

if you turn the engine off and back of to ignition is the temp still high or does it go back to the middle?

mines been playing up recently making me think its overheating but if i flick the engine off and then back on it goes back to normal, i believe its a faulty dask sensor on mine.

the 20v's have 2 sensors, one for the ECU (2pin) and one for the dash (1 pin), could this be why it looks to be overheating without the fan?

Ry

Hey,
Yes, there is enough coolant in the car. The oil is perfectly clean, and my heater is blowing hot when I set it to.
I don't know how to tell if my thermostat is opening though?

Also, haven't tried turning the engine off and back onto ignition to see if the temperature remains high, but i'd guess it's OK and doesnt do that as when i'm in a traffic jam the gauge creeps up - it doesn't suddenly jump up, and thern it goes down when I get into clear air.

I have a 16V if that helps.

Mark

Right, phoned up local fiat dealership today to find out how much a new coolant temperature sensor would cost (the one joined to the inlet manifold). I don't have a fan switch as it's controlled by the ECU in my model (2001)

They have told me that if the temperature gauge is working then there is no fault with the coolant temperature sensor and the fault lies within the ECU, meaning I will need a new ECU.

Is this right? It doesn't sound right - I thought that there are two thermistors in the coolant temperature sensor (there are 4 wires coming off it), one for the ECU and one for the gauge, so surely if the one for the ECU isn't working the gauge would still work?

Help desperately needed please!

You could get a diagnostic reader on e-bay for £30? This tells you what all the sensors and temperatures are reading in real time. Your car is the same as mine and EOBD compliant. If you live near Swindon I can hook mine up for you?

I had a car once that did a similar thing to this. The problem was the water pump. The impellor had sheared from it's shaft and therefore only spun very weakly. Okay when the car was moving with the rad helping to cool the slow water flow, but overheating when stationary.

If it starts to overheat in traffic, put the interior heater and fan on full and open the windows. At least this helps to lower the engine temp for a while!

Thanks for the reply.

I live quite a way from Swindon, in Lincolnshire

If I got a diagnostic reader, what should I look for, or what would I do with it?

I've ordered a replacement coolant temp sensor just in case it is that, that will come and be fitted Tuesday. Hope it isn't the ECU!

You could at least see what the ECU was reading from the sensors during a drive. I doubt it would be the ECU.

Have you tried flushing the cooling system and re-filling. Is the car losing
coolant? Does the heater work all the time? Is the fan coming on at all when driving or sitting in traffic?

Thanks for the reply.

No, I haven't tried flushing and re-filling the soolant.
The car isn't losing coolant, it's stayed at a level point since I bought it a year ago.
The heater does work all the time, yes. It also does blow hot air when I set it to.
Nope, the fan doesn't come on at all. I've let the temperature gauge go to the dot before it goes into the red and it hasn't come on.

Any ideas?

How did you check the fan relay? Did you measure the resistance across the switching contacts as it operates?
If the internal relay contacts are worn it could still cause problems. Is there 12V at any time on the AG and R cables controlling the relay. If there is the ECU is fine and is trying to operate the fan.

Also check the ground feed and connection coming into the relay from 8 on the attached drawing. If this is broken the fan won't ever come on!

The 30A fuse at 129 must be okay as you already ran the fan by grounding it? Relay is 122, fan is 154.

Hey, thanks again for the reply.
Yes, we measured the resistance against the switching contacts as 12V is fed to it, everything there was fine and when 12v is fed to the relay independently the relay switches fine.
I don't understand what you mean about there being 12v on the AG and R cables controlling the relay - surely these would only come on when the engine is hot and the ECU tries to switch the fan on? If there was 12v permanently the fan would always be on?


EDIT: Wait a sec - where is the coolant temperature sensor? Is it the thing at the front of the engine, underneath the metal plate and in line with the front of the battery; or is it at the side, with a yellow coloured thing, in line with the back of the battery?


Thanks
Mark

I do mean when it is hot, otherwise as you say, it would be on all the time. If this doesn't ever have 12V across it, the fault must be the ECU, temp sensor or cabling from the ECU to relay or the sensor.

Not sure actually one the car without looking at mine but item 279 is the sensor on the drawing.

You should check the continuity of the cabling from the ECU plugs to the relay and to the sensor. This would rule out a wiring fault. You could also measure the resistance across B1 and B2 on the sensor. This should have a linear change with temperature as the car warms up.

Worst case for you is if the ECU fan output is fried. If this happened to me I'd fix something similar to one of these:

http://uk.rs-online.com/web/search/s...uct&R=0331556A

in a suitable location and run the relay through that instead.

Hopefully your new sensor will solve your problem.

Right, we just tried unplugging the plug from the coolant temperature sensor and putting two 100 Ohm resistors across the plug to replicate a coolant temperature of 120degC.
Upon starting the ignition, the fuel gauge only shows at half temperature and the fan does not come on.

Does this signify the problem lies within the ECU? Also, we got the resistors the wrong way round one of the times and now the ECU light is on the dash all the time, even when the plug is plugged back into the sensor...typical :P

Getting the fuel gauge to read temperature must indicate a serious fault

Seriously though, did you put the resistor across B1 & B2? This is the one the ECU reads. The other is only the gauge. If this doesn't bring the fan on, then the sensor cannot be the problem. That leaves the ECU or wiring/connectors.

The ECU light probably came on if it went way out of range when you were messing with it. You'll most likely need to clear this using a disgnostic reader.

I'd triple check all the wiring or failing that bypass it. You really need to use a reader to see what the ECU is seeing temperature wise. If this thinks the temp is wrong, it will also fuel differently depending on what it thinks the engine coolant temp is.