I am running all fans while driving. thermostat indicator swings between kind of cold to medium on short trips recently. What is this an indicator for and what to do ?
It is called a coolant temperature gauge and it tells you if he engine is properly warmed up. It starts “cold” and should be about mid when he engine is warm. If it goes to the hot side, turn off the engine and let the car cool back down.
What fans are you talking about? The heater fans controlled from the dashboard of the car? They have little connection with the gauge previously mentioned. If not those fans, what fans?
1 Like
thank you, I was mentioning the heating fans because the car doesn’t seem to over heat. What I observed is simply the temperature meter being steady one day at middle , then another day it skips around oops to cool, not quite on dead point though, then jumps to middle then drops, it dances around when it should be steady. Am I to worry or replace something?
Depending on how fast the temperature changes, it may be the gauge itself. If it changes quickly (in seconds) it is probably the temperature sender or possibly the gauge. If it changes in minutes, it may be the thermostat that maintains a steady temperature in the engine needs to be replaced. Both are inexpensive and can be changed at the same time.
Only the thermostat is serious as running the engine too cold is not good for the engine or your fuel mileage.
If the gauge doesn’t work, OK, you don’t know what the temperature is but the engine will run fine.
Hah. Be carefull with what you are - well, writing. A friend of mine owns a -98 Rover 75. The thermostat cost pennies, but changing it is a 6 hour job for the experienced. That sounds insane and it is. But what can you expect from the brits. 
Hmmm Rover. Wasn’t that the company called the English Patient when BMW owned them? … and then closed them? 
Have someone check if there’s air in the cooling system.
Coolant temperature sensors don’t read air temperature very well.
So if a bubble of air comes in contact with the temp sensor, the temperature gauge will drop.Then when the air is no longer in contact with the sensor, the temperature gauge reads normal.
Tester
Yup, they were also a patient. Like the rest of brit car manufacturing.
Here’s my three guesses
- Air in cooling system
- Cooling system not holding pressure
- Radiator fan control malfunctioning
The first thing to check is the coolant level. Do this when the engine is cold. Not just the level in the plastic bottle, the radiator too. It should be at the full-cold mark in the plastic bottle, and nearly overflowing at the radiator.
On some vehicles the heater’s Cold-Hot control actually adjusts a valve that controls the flow of coolant to the radiator core. Making sure the heater is set on Hot and that that valve is open all the way is part of getting air pockets driven out.