Temperature Gauge only works over 70mph!

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Ok, drive it about normally and see if you get any heat out of the blower, if you do not and you get only a slight amount when your doing 70 in my experience its the thermostat. Mine never went over the 1st white bar on the temp gauge until I was going about 65-70mph then it would go up a little (just under half) with just a little heating.

Also, has it ever worked properly since the engine was changed? And if anyone here knows the resistance readings off the sender its likely you can test the system with a multimeter.
 
When you get to 70, does the needle suddenly jump to the position shown? Or, does it slowly climb to that position over the next minute or so of travelling at 70mph? I used to have to do 55 to 60 for about 12 miles for my temp needle to climb up a bit. It dropped straight back down when I slowed down. Thermostat was stuck open.
Thank you, that's exactly what it does!
 
What Defender 90 do you have? Mine's a 300Tdi.
On mine, this is the thermostat in it's housing at the front of the engine.
IMG_5785_zpsuallvotz.jpg


This is my stat, which was stuck open. You can see the gap
IMG_5786_zpsdxfkjqq0.jpg

It doesn't take much of a gap to allow the water to flood through to the radiator, the water is then being continuously cooled. So, temp gauge doesn't go up until you are burning a lot of fuel, fast, for a long time. It's an easy job to change. Get the tools out, swap new one in, put tools away = 20 mins.
 
Have you taken the bit of wire off the sender and shorted it to earth? (You can do this with or without the engine running)
If not, try that and you should get the needle to fully swing over to the very hot on the gauge.
If it doesn't, then you have a fault in the wiring!
Start with the simple stuff first ... ;);)
 
What Defender 90 do you have? Mine's a 300Tdi.
On mine, this is the thermostat in it's housing at the front of the engine.
IMG_5785_zpsuallvotz.jpg


This is my stat, which was stuck open. You can see the gap
IMG_5786_zpsdxfkjqq0.jpg

It doesn't take much of a gap to allow the water to flood through to the radiator, the water is then being continuously cooled. So, temp gauge doesn't go up until you are burning a lot of fuel, fast, for a long time. It's an easy job to change. Get the tools out, swap new one in, put tools away = 20 mins.
My Hero! Thermostat replaced & all is now well
IMG_7303.PNG
 
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