Technical Power failure when hot

[Notamechanic]

When hot the car loses all battery power and makes a strange whirring noise and threatens to cut out.
What could cause a loss of power when the car is hot. It starts fine when its cold again and its getting worse.

After a 50 mile run at the weekend it would not start at all this morning and the battery and alternator are fine. It will jump start and behave until it gets hot again. When its hot even the windows will not go up, no power at all!
HELP!

Its an older Fiat cinquecento, was once top of the range, SX i think.

 

[fingers99]

The whirring noise is probably the fan. If it stays on too long, it might because the engine is overheating, which might impose too much drain on the battery (especially if the fan is on its last legs).

 

[rallycinq]

echo echo echo

Cheers

D

 

[fingers99]

I think he didn't like my answer so posted again. Bet he likes yours less!

 

[Notamechanic]

Sorry, I only just got to work.

Thats a good thought and may well be the problem, nice one! Does a fan on its last legs drain the battery more than normal then? A friend suggested the starting motor could be draining the battery but i didn't really buy that.

Any thoughts very gratefully received - its my g-f's first car and I am entrusted with the job of fixing it...the amount i know about cars could fit into one short paragraph

Cheers

 

[rallycinq]

Take the connector from the switch in the side of the radiator. Open up a paperclip and insert one end into each side of the connector. Switch on the ignition and observe the paperclip. The fan should come on, and the paperclip should do nothing. If the clip is glowing or smoking, the motor is on its way out and needs replaced.

Cheers

D

 

[Notamechanic]

Wow! You really know about cars mate! Many thanks, I am genuinely impressed!

I will try that tonight when I get back and I will let you know what happens.

Thanks again!

 

[rallycinq]

Wow! You really know about cars mate! Many thanks, I am genuinely impressed!

I will try that tonight when I get back and I will let you know what happens.

Thanks again!

Old age does have its advantages

Cheers

D

 

[Notamechanic]

Is this the switch you mean - this is the side of the radiator and you can see the fan there which also has a switch under it.

Also, there are two pins, positive and negative presumably, going into this switch. I am not sure how to test this using a paperclip? Do I need two, one for positive, one for negative?

Confused.. ... sorry but please reply.

 

[fingers99]

It's the one on the radiator. The one on the fan is just a connector.

You need one paperclip: you use it to bridge the two contacts (while the wires are still there) to trick the fan motor into switching on.

 

[Notamechanic]

I feel rather thick here

two pins from switch into two pins on radiator. If i bridge the two pins on the radiator then presumably, not being plugged into the connecting lead, there is no power coming in so presumably nothing will happen.

if i connect the two pins in the incoming switch with a paperclip i feel i may well blow my arm off... ..not so good... by shorting/fusing the electric current.

yes, a bit thick, but I dont understand what to do...

two pins in photo on radiator = 1 side of switch
two pins on incoming connector lead = 1 side of switch

What next :idea:

 

[fingers99]

The switch on the rad only has 2 wires going into it, yes?

The switch works like this. One wire goes to earth, the other to the connector on the fan. When the water gets hot enough, the contacts within the switch close which completes the circuit. The paper clip completes the circuit so the fan should come on whatever temp the water is at.

But, of course, the wires have to be in place or the current can't get to the fan.

What you're looking for is for:

a. The fan to go on

b. To check whether or not the paper clip gets very hot (some needlenose pliers to pull it out). Rallycinq has seen them running red hot where the motor is fubared.

So, with that done we'll know if the fan is the cause of the flat battery. What remains is to check why the motor is overheating (in town you'd expect the fan to come on, but on motorways?)

 

[Notamechanic]

Now i feel like a complete idiot.

I understand the theory here, but the connector is a sealed plastic pin plug, its either stuck in the connector with plastic around it, or, you undo the little black plastic clip and pull the lead out of the connector.

If its plugged in then you cannot see the pins or the socket as it is enshrined in its plastic coating. If its not plugged in then clearly it wont work.

I understand how the fan works now (thanks) and presumably you connect the 2 pins to socket in the normal manner and then place the paperclip between the two whilst the ignition is on. trouble is, i cannot see how you can do that when they are encased in pretty robust plastic which covers it all up when you plug pin to socket.

See what i mean here? I am not hacksawing away the plastic to bare the connectors to stick in a paperclip, that is just insane. Isn't it?

 

[fingers99]

Panic not. Rallycinq should be along any second (and -- it's his method -- will be able to explain better than me).

 

[rallycinq]

Here I am, sorry for the delay.

Take the plug off the switch in the radiator. There is nothing further to do with the radiator.

With the plug in your hand, you have found two connectors inside the plug. No need to remove them, you can just plug one end of your 'U' shaped paperclip into one connector and the other end into the other.

So now you have a plug with an inverted 'U' sticking out of it. There is usually enough slack to be able to bring the plug assembly up above the slam panel so its easier to see.

Then switch the ignition on, it doesn't matter if the engine is hot or not, the fan will/should start to spin.

At this point look closely at the paperclip, but do not touch.

Hope this makes more sense.

Cheers

D

 

[Notamechanic]

thanks, that makes far more sense, i will try it out.

thanks again

 

[Notamechanic]

Well that didn't work. the fan is fine - its something else that cuts out the power, i took it for a run and the electrics just cut out and it starts running only on its own dynamo. What would cut the circuit out? Any thoughts?

 

[fingers99]

I understand that the fan works, but we knew that anyway. The object was to see at what point in its lifespan the fan motor was at. How hot did the paperclip get?

For the rest,

i took it for a run and the electrics just cut out and it starts running only on its own dynamo. What would cut the circuit out? Any thoughts?

I don't know what you mean. What is the "it" that starts running?

My guess (nothing more): either the fan motor is dying and that -- combined with running too hot -- is causing battery drain or, the car isn't overheating, but the negative feed from the fan switch is earthing out, causing the fan to come on.

It may be something else, but no way should the fan be coming on during motorway driving.

 

[fingers99]

Further thoughts -- I have to admit that this one has been puzzling me.

Is this right:

the engine cuts out, none of the electrics work except the fan? There are no warning lights?

Strangely -- or maybe not -- the fan effectively has its own earth. Just about everything else uses one of the earth leads from the engine bay.

Try this, will cost you little. Get hold of some vaseline and a file and some glass paper (or suchlike). One at a time, take off the earth leads (they're the fat, black, braided cables) at both ends, scrape/sand/file it all clean, coat with vaseline, bolt back together. The main earth lead bolts to the top of the gearbox.

Clean up well the leads to the battery as well, and use the vaseline.

 

[Notamechanic]

Sorry been hectic at work.

The 'it' is the car. I took it for a run and basically its is earthing out, something is preventing the electrics completing their normal circuit and you cant turn on the wipers etc... as i explained.

I will try and clean the earth but really it looks fine. I am not convinced the fan has much to do with it but the fact it has its own earth is a revelation and that could be it. Whatever the problem is, it is definately getting worse. The paperclip didn't get hot, i had it in there about 30 seconds and no heat or problems there.

I think it has to go to the garage sadly. I am puzzled as well - its such a basic engine (even to me). Something, somewhere, is preventing the normal circuits completing as they should.