325es Coolant light

[97audia4]

My 86 325es has a coolant light on the overhead diag display. If i drive the car about 20 minutes or so the temp gauge will read only 1/4 heated up or just slightly over but If I shut the car off and get back in 5 minutes later it is right at half way mark and the coolant light was off. Im thinking its the thermostat that is bad but Im no m20 expert either.

[101]

The light on the overhead display is for the coolant level only. Its a float switch that turns on if the coolant level is too low. Start with this and make sure the coolant level is up to the line on the tank when the engine is cold. If everything on your car is operating correctly (big IF), it sounds like you have low coolant level when cold that registers OK when the coolant is hot (as it expands in the tank).

Now on to the temperature gauge:

If the temperature gauge on the dashboard is still reading low, it could be the thermostat sticking in the open position, a bad temperature gauge sending unit, a flaky gauge connection in your instrument cluster or an overactive fan clutch. I'd suspect the thermostat first. If you have no idea of when the thermostat was last changed, they are cheap and relatively easy to change. Its also a good time to go over all the hoses and make sure they are in good shape. They don't last forever and a broken hose will leave you at the side of the road on a good day or overheat the engine on a bad day.

Make sure to follow the recommended bleeding procedures when refilling the system if you get into the thermostat or hoses.

[97audia4]

The light on the overhead display is for the coolant level only. Its a float switch that turns on if the coolant level is too low. Start with this and make sure the coolant level is up to the line on the tank when the engine is cold. If everything on your car is operating correctly (big IF), it sounds like you have low coolant level when cold that registers OK when the coolant is hot (as it expands in the tank).

Now on to the temperature gauge:

If the temperature gauge on the dashboard is still reading low, it could be the thermostat sticking in the open position, a bad temperature gauge sending unit, a flaky gauge connection in your instrument cluster or an overactive fan clutch. I'd suspect the thermostat first. If you have no idea of when the thermostat was last changed, they are cheap and relatively easy to change. Its also a good time to go over all the hoses and make sure they are in good shape. They don't last forever and a broken hose will leave you at the side of the road on a good day or overheat the engine on a bad day.

Make sure to follow the recommended bleeding procedures when refilling the system if you get into the thermostat or hoses.

Im not 100 percent sure when it was last changed, I know the timing belt was done about 5k before I got it but there was no mention of the water pump or thermostat being done. I have an extra set of hoses that are in good shape if it needs one.

I have checked the connection in the behind the cluster and tightened the little brass nut. Im going to order the two prong coolant temp sensor this week as well and eliminate that as a possibility.


It seems to have been taken fairly well kept so my plan is just to go through and make sure its up to to date and turn into a good daily.

[101]

The dashboard temperature gauge sending unit is the single pronged sensor.

[long tall eta]

do you have heat? the indicator lamp is just a sticking level sensor.