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Just had the garage renew & repair rear suspension arms and brake pipes and after taking her out on the road noticed the temp gauge rising up into the red it went ,so I stopped in a layby to let her cool down. Once cooled I checked the header tank and all seemed ok. Returned home and let her cool down overnight. Next day checked the header tank and replaced about 1 litre of fluid and no issues for a week until yesterday the temp gauge rose a little then went below the normal level and then returned to normal! I had replaced several months ago the thermostat housing, water pump and header tank and pressure tested. No visible signs of any leaks, I have not replaced the Engine temperature sensor.
Any ideas?

Is it low on coolant again? If you had to put a litre of coolant in last time, you've definitely got a leak somewhere. You haven't said what car you've got, as there are differing aspects of the cooling system on the different models.

Paul

FWIW I had a steady loss of coolant, often nothing much, but then about 0.5 ltr on a long drive. I turned out to be a leak where the bleed pipe leaves the header tank. Despite the apparently obvious place, it wasn't obviously the cause - no pools of water to give the game away - and it was only when happened to open the bonnet immediately after an intermediate length trip I could see water issuing from the root of the bleed pipe. My guess is that it required the water hot enough to raise the pressure sufficiently to blow out from the split, so short journeys didn't get hot enough (mine is a diesel, and they take much longer than a petrol engine to heat up), and on long journeys all the water had escaped before I next looked under the bonnet. The undertrays mean that if you see water on the drive, you have no idea whence it originated, as it will flow to the lowest point of the tray before dripping out over the nearest edge.

Cure was a new header tank, and taking care that the bleed pipe was properly supported in its run across the front of the engine - one of my pipe clips had broken or been attacked with a knife during service.

Paul,

I had a similar problem on the header tank of my 4.2 X350. The small pipe at the top seemed to cause a tension on the plastic spigot and it slightly fractured, but difficult to see. Fortunately, it's a known problem on the 4.2 and I could see traces of leakage after a run on the pipe spigot. As with you, it annoyingly needed a whole new header tank to resolve.

Paul

I had something similar to Paul but turned out to be a weak clip allowing coolant to seep past it.
Sorted with a new clip.
Tony

Petrol Xj350 2003 is my car, sorry forgot to say!
So far she has not lost any fluid since top up but the fan comes on although the temp gauge is normal and when I stop the fan runs for a while but in saying that I went out today and the fan did not come on once? Which tells me a sensor is playing up or am I being too simplistic?
Anyhow I am ordering a new MAF sensor and Engine Coolant Sensor as looking at my cars history they both have never been replaced and she has just completed 150K (I have the cars history from 2007 to present).Thank you guys for your input it is much appreciated!

Going to check pipe clips as header tank is new ( Many thanks PaulGover)

V6 or V8 engine?

Paul

V8 engine

So far to this date I have not lost any coolant! Temp gauge staying normal but have bought a new coolant temp sensor.
Anyone know where I can find the engine coolant sensor?? It's hiding from me