O/T Mechanical advice please!

[Mon Ami Mate]

I'm at my wits end with my girlfriend's Cinquecento. It suffered a head gasket failure last year, which was "rectified" by a Fiat dealer (lots of experience of them as an Alfa fan - none it pleasant).

Recently the car has started running hot. We've had it looked at by several mechanics, all of whom report that they can't find anything wrong with it. It just gets hotter and hotter until it boils over. The head gasket hasn't gone again (no oil in the water), the thermostat and water pump are appraently functioning as normal.

Can't think of anything else to investigate...unless you know better!

[whatever]

I'm not much of a mechanic, I'm afraid, but have you checked that the system has been properly bled and there isn't an airlock in there somewhere?

[ZZR600]

is the cooling fan working ??

[thub]

Is there a bypass mechanism (that allows a quicker warmup by avoiding the thermostat) that isn't working or has a blocked/collapsed pipe?

[adrianr]

- Does the radiator fan come on as normal?
- Any coolant loss if you run it a bit (not to overheat) and then shut it off?
- Anyone done a pressure test on the radiator system or a leakdown test on the cylinders?

It is possible for a head gasket to fail such that combustion mix blows into the water without any water getting into the oil.

Do you know how it failed and what they did to fix it? If you're really unlucky, overheating can soften aluminium cylinder heads so they won't hold a gasket.

AdrianR

[plotloss]

A block somewhere in the cooling system would be my guess. As the engine is overheating is the heater kicking out hotter and hotter air? If its not its probably a block/air lock IIRC.

Matt.

[M-Five]

It could simply be a faulty thermostat not sending the signal to the colling system to switch the fan on!

[Mon Ami Mate]

Thanks for these chaps - some extra food for thought here. The fan does come on - it just can't cope. I'll definitely try bleeding the cooling system and eliminating any possible air locks.

[Tabs]

The head gasket may have gone again. A quick check is to get the emissions checked, but not at the tail-pipe! With the rad cap/expansion cap safely removed, and with the engine ticking over, put the probe close to the bottle top. Readings may show gasses in the steam. Not fool proof but a help.

[clositintelctual]

It is possible for the impellers on the water pump to shear off, I have seen this on at least 5 cars in the last 8 yrs, mostly vauxhauls. This sometimes causes a dreadful noise but occasionaly the broken off blades just fall to the lowest part of the system and sit there doing nothing. two ways to test this; remove the thermostat and take off the top hose on the rad, start the engine and see if water is pumped out of the hose, it should come out at a fair rate. Alternatively remove the water pump and look at it.

[Mon Ami Mate]

Thank you Chaps. I know what I'm going to be doing on Sunday afternoon...

[mondeoman]

You could also check the rad for blockages inside and out - the odd bird (feathered of course) can cause a few problems and you'd be surprised at the amount of gunk that can accumulate inside a cooling system.

[gtir]

Also the thermostat could be faulty, as in not opening so the there is no circulation?