We went to see a 1998 Felicia last Saturday, had a test drive and noticed the temperature gauge was reading low, about 70. The garage said they'd fix it, guessing the cause to be an always open thermostat, and get it MOT'd as well. Collected late this afternooon, and when starting to head for home the needle was slightly above horizontal, which seemed about right from what I remember of our previous Felicia.

That thought was obviously too soon because we joined a traffic snarl-up ... diversions after an accident, nose to tail stop-start for best part of an hour. The needle quickly rose to 110 - a bit of a surprise - but then stayed at about that level, dropping slightly as the fan cut in, then rising slightly after the fan stopped. I turned on the interior heater fan just in case.

After escaping the city and joining a motorway the car seemed OK but after maybe a quarter of an hour I noticed the temperature was getting very low and still dropping. There was still a lot of warmth coming out of the interior heater vents so I suspected an air-lock. This seemed more obvious when, shortly after, the air from the vents started to get cooler.

I stopped to investigate. The cap on the header tank came off easily, as if there was no pressure build up in the system. Is that normal? I ran the engine at slightly above idle revs in an attempt to clear out a possible air-lock. It seemed to work as, eventually, the reading on the temperature gauge lifted off the minimum and headed towards the normal region.

This was enough for me, so I put the top back on the header tank and continued my journey.

The temperature started falling again, and a little while after the needle had reached the bottom of the guage the air from the vents felt cooler. The sequence was repeated a number of times before I got home :(

Does anyone recognise these symptoms? If so, what was the cause?

I'm still thinking an air-lock is possible, but now I'm also wondering what the garage could have done to fix the cool running problem, (other than replace the thermostat), and whether the cool running was the symptom of some other problem.

After some thought and experimentation I've concluded that I deluded myself when collecting the car - it had been delivered a short distance so the engine would have partly warmed up when I got into it, hence the initial and apparently reasonable temperature shown on the gauge.

The fan definitly is working correctly. When starting from cold the needle eventually rises to 110, at which point the fan repeatedly kicks in to stop the temperature rising further.

When the temperature is at 110 there is definitely pressure in the cooling system - which means the reason for no pressure on the way home was that the temperature really had dropped off the bottom of the gauge. This in turn points to the thermostat being stuck open, and the cobwebs in the engine bay point to the garage not actually making an attempt to fix the problem.

Off to buy (or order) a thermostat ...

You checked for possible HGF?

No mayonaise in the header tank, nor on the dipstick, nor under the oil filler cap.

The oil in the cap is bit horrible, which fits with it not being serviced for four years, during which it appears to have covered only 10,000 miles, (backed up by MOTs).

Edited 24 April, 201115 yr by AnotherGareth