Coolant temperature gauge unstable

[maurice78]

Hey!

I have been searching around the forum, and it seems similar to some other recent topics about it, but I am not sure if it is the same problem.

It is cold here in Norway, -5 degrees celsius, and since a few days my coolant temperature gauge is "dancing around". It goes from very cold, to overheated, and back again. It is very unstable, but moving slowly.

The coolant levels are okay, and it is quite unlikely the engine is overheating in this weather. Also I do not see an effect on mpg and have no difficulties starting. My car is a 2003 V40 1.9D.

Could it be the coolant temperature sensor, and if so, where can I find it?

[m1tch1987]

Hi there!

It might be something like a thermostat stuck open, this means that the engine never really gets warm as its always being cooled down although does your heater work properly as in if you put it on hot is it very hot or just warm?

It could indeed be an issue with either the gauge or the sender if the heater is working as it should although its been known that themostats get stuck open.

[maurice78]

Sorry for replying so late, I had to drive a longer distance to see if my heater is functioning properly.

The heater is not really producing hot air, more warm, so you might be right. I don't know if it is related to the cold weather. I could imagine that because it is -10 degrees, it is not able to heat up the air so very much.

How can I determine if the thermostat is stuck open, or should I go by a mechanic?

Thank you very much for your help, I appreciate it!

[mikealder]

You take the stat out to check it, test it in a pan of boiling water, although once you have got the old one out you may as well replace it with a new one as ther don't cost a lot - Mike

[tt82]

One way would be to try different thermostat or temp sender. I'm currently tryin to sell both of those parts from my spares box. Your welcome to a try before you buy deal but not sure what the postage to Norway would be.

[maurice78]

Thank you all for your replies! I am going to take a closer look at the thermostat and temp sender, and when broken I wouldn't mind to buy them from you tt82.

One more thing that I noticed. When I hit the gas, and the fuel usage goes up, the coolant temperature gauge goes down:

(short video while driving and hitting the gas, turn down the volume though)

http://youtu.be/1_2J58y8oCY

Does this confirm the diagnosis of a defect thermostat?

[KBB]

When the temprature guage drops is the a drop in temprature of the in coming air from the cabin heater. If so then I would say the thermostat is sticking. Might just be worth sticking a thermometer in the air vent and just see if the is a temp drop in sequence with the guage drop!

[tt82]

Originally Posted by maurice78

Thank you all for your replies! I am going to take a closer look at the thermostat and temp sender, and when broken I wouldn't mind to buy them from you tt82.

One more thing that I noticed. When I hit the gas, and the fuel usage goes up, the coolant temperature gauge goes down:

(short video while driving and hitting the gas, turn down the volume though)

http://youtu.be/1_2J58y8oCY

Does this confirm the diagnosis of a defect thermostat?

How about £10 for both the thermostat and sender plus p&p. Pm your details if you want them.

[Dog_Book]

What car have you even got? You will find the early cars like mine have a different sender for the in car gauge as i now have 2 new senders ;/

[Biotoxic]

Originally Posted by maurice78

One more thing that I noticed. When I hit the gas, and the fuel usage goes up, the coolant temperature gauge goes down :

thermostat is stuck in a open position.The faster yo drive the lower will be the coolant temperature.