Hi everybody. It seems that the peach of a car that I though I had just bought isnt so peachy afterall. The car overheats when kept at a steady speed on the motorway (65-70mph). It is ok around town and even if left standing at idle for half an hour the temp will stay steady. There is no air in the system and there is no loss of coolant.The coolant is not contminated either. Also, the water pump seems fine. The only mystery is that even when the engine is hot enough to trigger the fan, the radiator is stone cold (although the pipe that comes out of the thermostat to the radiator is hot) The garage says no faults can be found, but that does not help me and my family when we have to stop every 10 or 15 miles on the motorway when the temp goes into the red. Fiat say that the temp sensor would not malfunction like this either and any sensor fault would register on the dash display. Anyone had a similar experience? any thoughts?

Faulty thermostat. I'd put money on it. Baring that, how have they checked the water pump?

There's certainly something half blocking the circulation

When your engine's over hot but your radiator's cold then it could be thermostat (although they tend fail open rather than half closed)
Air in the system
Blockage in the radiator


Does the heater work properly? Is it blowing cold at times? = air in system

CHECK YOUR THERMOSTAT
Start engine from cold and feel the hose next to thermostat. As thermostat gets to trigger temperature you should feel a sudden rush of heat as the thermostat opens. If not then thermstat isn't working properly

RADIATOR BLOCKAGE/AIR
With engine warmed up and at idle put your hands around the radiator inlet and exhaust hoses (keep hands clear of the fan). One hose hot whilst the other stone cold = radiator blockage or air in system.
Feel the radiator top to bottom, any massive change in temp?= air/blockage in radiator

In the meantime, put your heater on full blast when the engine's getting hot to bring down the temperature until it's fixed otherwise you'll risk blowing a head gasket

I told the garage that I though the thermostat was faulty, but they would not entertain it. They said that it would also overheat during normal driving conditions and it remained within normal temp range when they took it for a test drive (all 100 miles of it!) Needless to say, they probably did not drive at normal motoway speeds for 10 or 15 miles. In any event, I now have a car that I cant take on the motorway, but the garage wont fix because they say it aint broke! Maybe I should just keep going next time it overheats and let them pick up the bits when the head gasket goes or when it seizes! Thanks anyway.

If your thermostat is failed closed your engine will overheat as soon as the engine comes up to temperature
if it's failed half way then it will take longer to heat up and overheat on possibly on faster driving.
If it's stuck wide open then it will never heat up properly and run cool all the time at faster speeds

I'd investigate the possibility you have a blocked radiator/ air in system

There is a possibility head gasket gone at high temps but investigate others first

Do the checks I outlined above, they're easy to do

Thanks deckchair5

As i mentioned in my original post, the pipe on the outlet side of the thermostat is hot but the radiator is stone cold top to bottom. I doubt a blockage of the radiator because if I squeeze the pipe on the right side of the radiator I can see the pipe on the left side of the radiator pulse in and out. I also think that that the thermostat is partially faulty, maybe stuck slightly open so not enough cooling at motorway speeds. The heater is fine. However, what do you do when a garage says no fault and wont fix? Maybe I can get my money back, afterall, I have only had the car for 8 days.

I guess you mean the radiator inlet pipe is HOT
The pipes will still pulse when squeezed if you have air in the radiator If you have that massive change of temperature across the radiator with the car not moving then there's something wrong in the radiator. Air most likely

Temperature will be almost the same inlet to outlet with car stationary

Do the thermostat check i outlined above. A sudden rush of really hot water means your thermostat isn't stuck

I to had the same problem with my 1.9 stilo it a 05 model with 57k on the clock. now they have changed the water pump, thermostat. but to no avail . then the rad started to get rid of the water as fast as I put it in I was told that there was impacted damage to the rad. they changed it on the way home that night it overheated again on the motorway I returned it the next day after a few days the gave it back to me saying that the found a blockage in the new rad.mmmmmmmmm that was about 3 weeks ago now what I find is that my car does not over heat but after been in sitting in traffic for a good while water starts coming out of the expansion tank which I have to fill ever day or so. This would lead me to believe that the overheating problem is not gone away.

kevin kilmartin said:

I to had the same problem with my 1.9 stilo it a 05 model with 57k on the clock. now they have changed the water pump, thermostat. but to no avail . then the rad started to get rid of the water as fast as I put it in I was told that there was impacted damage to the rad. they changed it on the way home that night it overheated again on the motorway I returned it the next day after a few days the gave it back to me saying that the found a blockage in the new rad.mmmmmmmmm that was about 3 weeks ago now what I find is that my car does not over heat but after been in sitting in traffic for a good while water starts coming out of the expansion tank which I have to fill ever day or so. This would lead me to believe that the overheating problem is not gone away.

Click to expand...

You don't say if temp. rises in traffic - does the fan come on?

If the fan is OK then it could be head gasket related - I'd get an accurate compression test done.

Kevin
When your water is disappearing, particularly when the engine gets over hot (opens up the leaks) and it's flowing out of the expansion tank when stationary and hot then that's a head gasket. Water's going out and air is going in- increased volume- pushes it out of the expansion reservoir
Water in the expansion tank hotter than it should be? Water surging up and overflowing? Then surges right back down again. Need to top up then overflows again? Lots of gurgling? Engine temp gauge going over hot then over cool? Sound familiar?