Coolant temperature

[nelmo]

I just got back from a 10-day trip to France. My RX400 was doing fine all trip until the long slog back on the autoroute. The temp gauge, which normally never moves from the centre of the dial, was all over the place. At times, it came perilously close to the H symbol, at other times, it dropped to just below it's normal central position.

I had checked the coolant level before we left - it seemed to be around halfway between 'low' and 'high' (difficult to see), so I stopped and topped it up with water (didn't have any proper coolant with me) but it made no difference, the gauge was still up and down for the rest of the trip.

Now, the fact that I could physically see the needle move up and down suggests that maybe the sensor is dying? The needle position seemed to be speed/rev dependent - at lower speeds, the needle stayed in it's normal position but at higher speeds or when accelerating, that's when it moved nearer the top of the range (although it still kept moving around).

I can't believe the coolant temperature was changing that quickly so I'm inclined to think it is the sensor - anyone have any other ideas?

[iwonder]

Sounds like air in the system causing sensor to vary. Check your radiator for a crack.

[nelmo]

Ah yes, that sounds plausible, although I haven't noticed any puddles (but I wasn't specifically looking either before)...

I used to have the service manual but lost it when I changed laptop - is there any way to get a copy from someone?

[Herbie]

@nelmo Just sent you a PM Neil.

[Barry14UK]

Be very careful as overheating can have knock on effects.  I had some loss of coolant on my V6 Camry some years ago now. I replaced radiator and coolant and all seemed well.  However, it became evident that a cylinder head gasket had failed. (not suggesting this is your problem),  So with new head gaskets all was well for a few miles but then oil warning light came on and to cut a long story short, the original overheating had caused the coating of oil in the engine to flake off and drop into the sump.  This had resulted in the oil strainer in the sump becoming completely blocked so starving the engine of oil.  So a good clean and removing hardened oil from strainer with a pick sorted the problem. Luckily I stopped driving quite quickly before significant damage was caused.  But this was due to the original overheating so it may be OK but if ever my car overheated, I would do an oil change in case flaked oil residue had been dislodged into sump.

[iLexus7]

Hi, was it actually air in the system or faulty coolant temperature sensor? 

[Greisingel]

Exactly same  for me on return from France. I bet you have the cracked plastic radiator shoulder. I had to crawl 200 miles on Battery, charged with topped up rad and ICE runs watching gauge.

Look for the white limescale deposits when you face the top left hand side of the rad