Jumping temp gauge and loss of power

Towing a caravan With a Defender TD5 up a slight hill on the A55 way back home after a 200mile journey, had to drop down to 4th gear then 3rd gear which I thought was unusual, the temp gauge shot up to the red, I pulled over and checked the engine, it seamed ok no signs of overheating, plenty of water and plenty of oil. Started engine again within minutes and temp was back to normal. Carried on the journey, next long hill it did the same 4th, 3rd gear again i thought unusual temp gauge shot up to red changed to 4th temp gauge shot down to normal then up to red then to cold (no reading) it stayed like that until we stopped. We started again temp gauge was back to normal. Does any body have any ideas?

what vehicle and engine ?

Defender station wagon 110 TD5 52reg

I'm having exactly the same problem with min. Thought I had cured it but it started again last week.
Is your TD5 standard or remapped?
I think my next step will be to change the Coolant temp sensor just to eliminate it.
Unless anyone knows better??

It could just be a dodgy temp sender, it could be summit like a waterpump going down, sticking thermostat or even a coolant pressure cap failing which means the coolant isn't circulating properly. There's no signs of coolant hoses pressurising I take it?

Hmm very good question.. I will have a feel when i get to work in the morning.

you need to check coolant level with bung on top hose out expansion tank level is no indicator of actual level it seem quite common for td5s to loose a little coolant and top hose often has air in it which makes temp sensor misread

Would a dodgy temp sensor cause a loss of power? Is it connected to the dreaded engine management!

accywingy said:

Hmm very good question.. I will have a feel when i get to work in the morning.

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4 days ago shifty had the answer to your problem about the temp sending unit I think it was a td5 coolant temp gauge, and it was yesterday.

john winsemius said:

4 days ago shifty had the answer to your problem about the temp sending unit I think it was a td5 coolant temp gauge, and it was yesterday.

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So is air in the system, steam pockets, etc etc

mmcbreeze said:

Would a dodgy temp sensor cause a loss of power? Is it connected to the dreaded engine management!

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yes ive had a few like that

ratty said:

So is air in the system, steam pockets, etc etc

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yes just in the spot where the sending unit is by the thermostat