Car mystery - any mechanics out there?

[loftus]

On Friday I noticed my N reg high mileage Fiat Punto appeared to be leaking. Couldn't be sure if it was water or oil - yes I am that inept. Appeared to be coolant. The engine also ran hotter than usual. Usually it sticks around 25% of the temperature gauge, rising to 50% when idling or going slowly in traffic - this time it was around 50% rising to 75%.
I topped up the header tank, which was around the minimum mark with water. Next day I drove from Colchester to Sudbury and back and to my in-laws and back at steady speeds and the temperature gauge was more or less back to normal and the leak appeared to have stopped.
Sunday I checked the header tank and it had dropped back to minimum. I topped up with coolant and drove steadily to various locations dropping off and picking up kids - again temperature normal and no apparent leaking.
Same again to day - topped up, no leaks, temperatue normal and car running normally.
I had been concerned that I had blown a head gasket, but the only sympton I have of that now is bubbles in the header tank - although when I stick my nose in I get no exhaust smells, just the smell of the coolant. My exhaust is clear - no steam. The engine is running well and the temperature appears to be, if anything, lower than normal. Just making 25% when driving and not quite gettimng to 50% when left idling for 10-15 minutes, although the fan does keep cutting in.
I have to drive from Colchester to London and back tonight/tomorrow morning for work and then I am dropping it off at the garage for them to have a look at.
Anyone got any ideas apart from a blown gasket - anyone give me hope that this isn't going to cost me £300+?

[chrisw]

Could be a faulty radiator cap. Might be worth replacing for what it costs.

[skiddy2k]

if it was the radiator cap, it should be obvious to you that there's a leak around it.

it looks to me like one of your heater hoses have split and therefore the coolant is leaking. try to notice if there's any traces of water underneath your car after you've taken it for a spin.

if its a small leak, put some 'radweld or 'bars leak into your radiator which you can pick up from your local halfords for about £4 quid. it seals small leaks in your radiator system.

Many people put an egg yoke into the radiator and this tends to do the same thing as the radweld and bars leak additive, but, i would rather use the proper stuff!

if this doesnt proove succesful, id say that its your thermostat in the car. thermostats have temperature gauges on them which tells the radiator when to cut in and cut out. i would say that the radiator isnt cutting out in time, therefore the temperature gauge is going up and the coolant in the radiator systems is bubbling/boiling out of the expansion tank or through the radiator cap.

hope this all makes a bit of sense to you, try it out,
hope it helps,
Skiddy

[loftus]

Thanks for the advice.

What I find baffling is the leak appears to have stopped.

I haven't had a chance to check the coolant level since this morning but I'll take a look before I go to work.

The temperature dropping back to normal has me flumaxxed as well.

The bubbles in the header tank were when I checked on starting the car and letting it idle. At no time did it appear to 'boil over' after that.

[chrisw]

if it was the radiator cap, it should be obvious to you that there's a leak around it.

Not necessarily. If the spring weakens, the coolant is ejected down the overflow tube when the system is hot/pressurised, so no leaks are visible.

I agree that a faulty/intermittent fan sensor could cause the same effect if it's not cutting in properly.

[bobbywomble]

i think it would be fairly safe to say that if your head gasket had blown you would know about it pretty guick by the rather upset police man coming at you from out of the smoke :rotfl:

there is a simple test for the head gasket
drive down the road at aprox 40 in 4th gear
look in the raer view mirror if you can see the car behind
and its clear your head gasket is ok
if you can only see grey smoke like bonfire night you got problems
the main problem would be water in the mixture of air and fuel and the result would be quite spectactular :eek:

it sounds to me as though you simply have a slight leak in either a hose or the header tank could be cracked
the way test this is to dry all the pipe work and the header tank off as much you can do then run the car on the drive or road stationary ant wait for it to heat up
then stick your head under the car and look for drips or steam the trace it back to where its coming from then replace the relivant part
should only cost about a tenner
if the header tank is split seal it up with high tempature non flamable sealant available from b&q it costs half what the car shops charge

[loftus]

Update- the mechanic had it today, gave it a good going over, took it for a long test drive and said as far as he could tell it was ok! Said to keep an eye on it but he couldn't find anything to do.

Thanks for the advice.

[wazza]

had a similar problem with my car years ago. found out that the heater matrix inside the car was leaking. feel around under the dashboard for a damp patch.

regarding blown head gasket you car will be overheating and in most case there will be traces of oil in the coolant and/or traces of water in the engine oil