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Hi all my hdi 90 has always run at around 80c for years anyway yesterday temp started jumping up and down indicating a new sensor was required, anyway i decided to change the stat and sensor but temp is now 85c but why if it was the sensor shouldn't this have happened when i got the car years ago

i think 80*c seems just a bit cool to be running anyway.
85* -90*c seems more like it to be running at optima temp

maybe your other stat was stuck open and not adjusting to optima temp

The top hose is hot and the bottom is a bit cooler is that normal theyre not hard just firm with the expansion

Took both old and new stats and the old one only opens 1mm but the new one opens at least 3mm

gray wrote:i think 80*c seems just a bit cool to be running anyway.
85* -90*c seems more like it to be running at optima temp

maybe your other stat was stuck open and not adjusting to optima temp

+1, when I first bought mine it ran at bang on 90, after doing a coolant flush & fitting a new stat mine then ran at 80 & took a long time to warm up
Anyway I decided to take the new one out to inspect it thinking it must be stuck open a bit, no such luck.
So I banged the original one back in & 90 again & quicker warm up times
All the car's I've ever had & that's over 20 have ran at 85-90 mostly 90 bang on.
If I remember corectly then stat for these should start opening at 85 & be fully open at 90
Hope this helps DDD.

I believe there are a number of different thermostats available, which open at different temperatures.

I couldn't find any diferent one's when I was looking so gave up & put the original one back in.

I think mine said it opens at 83c

When I was young thermostats used to have their temperatures stamped into them somewhere. They also failed rather a lot, even new ones, so it was advisable to test them before fitting them.

My HDi sits on the 9 of 90. The yoyo sits about half-way up, dunno if it's got a scale, don't care either.

i changed mine in the summer and seem to open just after 80c which seem a bit cool to me but i believe the correct opening temp is 83c, my car has also be mapped and had the egr deleted and there is a big difference in how long the car take to warm up takes about 8miles on a really cold day.

As stated above, there are different temperature opening thermostats available. Usually around 83C for summer use and 88C for winter use. There are allowed error parameters in the manufacture of thermostats and sensors, so it is not unusual to note slight differences in gauge readings as parts are replaced. The bottom hose should always be cooler than the top hose as the radiator is cooling the coolant before it re-enters the engine.