Heater & Temp Gauge Problems

zilog_jones

I got a '98 Fiesta 1.3 a couple of months ago. Got the thermostat replaced last week. However, when I was driving with no thermostat (on the way to get the new one put in), the heater decided to stop... heating. It just blows cold air now regardless of what setting. The two pipes to the heater matrix still get warm, and if I start the car while the engine is warm heat comes through for a few minutes, but now there's nothing besides that.

When there was no thermostat in it would heat, but would cool down easily if I turned up the blower and wasn't driving too fast. When the broken thermostat was in (it was stuck closed) it was always very warm (after about 10 minutes of driving), and was still quite warm when I turned it to cool

Any ideas? The mechanic who put in the thermostat said it was probably some electronic control that was gone.

Also, the temperature gauge isn't working - it just stays on cold - it's been like that since I got it. The Haynes manual describes some way of testing the gauge sender (IIRC it's a thermistor on a pipe somewhere) but I can't actually find where it is (the picture in the Haynes manual is crappy), and I'm a bit scared of messing around with car electrics (never done it before, big scary battery, etc.) . The mechanic said I'd prob have to go to a Ford dealer to get it sorted, and I hear the two in Limerick (Shiels and Lyons) are a rip-off.

And sometimes I notice a little hissing coming from the cap on coolant expansion tank after driving. Is this normal? Could it be anything to do with there being too much water in it? It's a good bit over the max level.

Thanks for any help

MercMad

Just to give you a basic guide..........the car starts from cold, so the water is cold and the 'stat is closed. Cars operate better when fully warmed so the idea is to get the temperature up as soon as possible. Once you are driving the coolant in the engine block is beling warmed, but there is minimal circulation. Then the 'stat opens and the warm water is fed into the cars heater system, assuming you have the controls set to hot.
From then on the water is circulated by the water pump througfhout the whole system, block to heater to rad and so on. If your 'stat is stuck closed the car will overheat, if it is stuck open (or missing) it will never heat up enough so generally it will run rich, burn more fuel, and never get anything more than cool air inside(depending on the car).

To me it sounds like you have an airlock in the system, all pipes should be the same temperature, i.e very hot. The wire for the temp gauge, from memory is on the drivers side, top of the head near the large pipe from the top of the radiator. If someone sits in the car and watches the gauge then you simply earth the wire off the engine, briefly. The gauge should reach max level after a second or so. if not you have a bigger problem.

fightin irish

As regards your heater blowin cold air...It's a heater valve...Situated up at the bulkhead with two pies going into and two pipes exiting. €50 ish.

SonOfPerdition

zilog_jones wrote:

And sometimes I notice a little hissing coming from the cap on coolant expansion tank after driving. Is this normal? Could it be anything to do with there being too much water in it? It's a good bit over the max level.

Thanks for any help

as coolant heats up it expands, and the pressure increases. cooling systems are designed to run under pressure (which raises the coolant's boiling point). Usually about 15psi. There is a pressure relase valve in the radiator to allow coolant to escape when the presure raises above 15psi. This overflow is routed to the expansion tank. When the coolant cools then a negative pressure is created and sucks the coolant back into the rad from the expansion tank.

So ... If you overfill the coolant in the expansion tank then it builds up too much pressure when the system exceeds 15psi as there is no room to put more coolant in, and you get the hissing sound as it escapes through the weakest point .. the expansion tank cap.

Nom-IzZ

yea as all ready said it is a faulty heater control valve that has troubled 99% of all pumas and earlier fiestas, it is really easy to replace but will prob go again due to bad ford engineering not been able to make the swing on the valve long enough and does not allow nuf cold water through, far as i remember a new part was due out to fix this problem, best to ring any ford garage and ask their parts dept!

zilog_jones

MercMad wrote:

To me it sounds like you have an airlock in the system, all pipes should be the same temperature, i.e very hot.

But all the pipes do get hot - I said even the pipes going to the heater matrix (along with any other pipes and the radiator) are hot after driving. Well, anything I can see anyway.

The wire for the temp gauge, from memory is on the drivers side, top of the head near the large pipe from the top of the radiator.

Yeah, that's what it looks like in the Haynes manual - I guess I'm not looking hard enough!

If someone sits in the car and watches the gauge then you simply earth the wire off the engine, briefly. The gauge should reach max level after a second or so. if not you have a bigger problem.

So, I just like disconnect the wires and earth them off the engine somewhere? I take it I need the ignition on? I have a multimeter as well if it's any use in finding the problem. Is it easy enough to replace the sensor?

fightin irish wrote:

As regards your heater blowin cold air...It's a heater valve...Situated up at the bulkhead with two pies going into and two pipes exiting. €50 ish.

€50? Gah, I guess I'll have to freeze till after christmas
I assume if that's gone, then the pipes after it going to the matrix and the matrix will be cold? Must check that.

SonOfPerdition wrote:

If you overfill the coolant in the expansion tank then it builds up too much pressure...

Should I just drain it a bit from the radiator? What should I do with the leftover water? I've never done anything with antifreeze before

Thanks for the help everyone!

fightin irish

Nom-IzZ wrote:

far as i remember a new part was due out to fix this problem, best to ring any ford garage and ask their parts dept!

I already answered