[BradMJensen]

I just replaced my expansion tank with an all aluminum performance one and there is no place for the coolant level sensor. Any ideas on how to get rid of low level dash light?

 

[Overboost]

Jump the 2 wires on the level connector.

 

[wfx32]

which one did you install .. moroso, mishimoto, csf or zionsville? i would expect the replacement tank to have somewhere to mount the stock level sensor.

i guess you could fix the wiring to disable the sensor, but i would want some notice of a coolant leak.

 

[Rob Dublin]

Drill and tap the new expansion tank to receive the stock senor at a sensible level?

 

[BradMJensen]

Thanks Guys!

 

[MrMCar]

Weld in? No can do.

The factory sensor is built into the tank, it's a float inside the tank. The sensor element installs into a dry cavity, sensing the level of the float inside the tank. It's not like the older cars where the plug, sensor and float are one piece.

His best option is to join the two wires together.

 

[74123]

I just replaced my expansion tank with an all aluminum performance one and there is no place for the coolant level sensor. Any ideas on how to get rid of low level dash light?

I presume you have a low coolant light on the dash. I don't know what the DME expects from the sensor in its rest state. Something or nothing. If it's nothing then just tape the connector up and put it to one side. Otherwise use a resistor or some other strategy to simulate the sensor's presence.

 

[Overboost]

I presume you have a low coolant light on the dash. I don't now what the DME expects from the sensor in its rest state. Something or nothing. If it's nothing then just tape the connector up and put it to one side. Otherwise use a resistor or some other strategy to simulate the sensor's presence.

My understanding is the sensor is a simple on/off, either a connection between the 2 wires or not with one being a ground. I don't think any resistor is needed here, just join the 2 wires. I don't think the DME even gets that signal, it goes to the cluster.

 

[IceWhite]

I presume you have a low coolant light on the dash. I don't know what the DME expects from the sensor in its rest state. Something or nothing. If it's nothing then just tape the connector up and put it to one side. Otherwise use a resistor or some other strategy to simulate the sensor's presence.

With it disconnected, the low coolant level lamps stays on solid.

 

[jmo69]

Drill and tap the new expansion tank to receive the stock senor at a sensible level?

It's a quarter turn fitting, no threads, are you thinking of the coolant temp sensor in the head?

 

[Overboost]

Isn't there a magnet in the expansion tank that triggers the sensor? It is not in any way submersed in the coolant. That's why there is no o-ring to seal it to the tank.

 

[MrMCar]

Your testing may have achieved the results you posted. So why is it when you remove the sensor from the bottom of the bottle no coolant runs out? Nor does it have any seal at the bottom.
Because it never makes contact with water (coolant). There is a float inside the tank. It interfaces (through the plastic) to the sensor that goes inside a sealed chamber of the bottom of the expansion tank.

Here's a E39 tank with the same engine. (cut in half)

https://www.bimmerfest.com/forums/showthread.php?t=505142

 

[IceWhite]

With it disconnected, the low coolant level lamps stays on solid.

I have a new Meyle water level sensor. I have just put a meter across the pins of this new level sensor. There is no continuity between them when the sensor is NOT immersed in water.

There is no continuity when I put the sensor in cold water.

When I boiled water and put it in a cup and then immersed the sensor in the water there IS continuity. There is clearly a thermistor in there that closes when it gets hot.

When I measure the resistance across the pins on the sensor the resistance reading continued to rise up to 60 KOhms and rising when I stopped. I imagine it might increase beyond the 60 KOhms.

So functionally it appears that continuity with about 60 KOhms = light out.

But you would have to experiment with the size of the resistor.

Therfore, in order to simulate water you need to establish continuity between the two holes in the connector that mate with the sensor pins. You need to do that using a resistor. You need to bridge the two holes in the water level sensor connector with the resistor and, based on these observations, your light should go out.

I have no way of measuring those pins or the holes in the connector that they mate with but they look to be a similar size to the diameter of the wire that you get on a small electronic component like a resistor. That is about 0.6 mm diameter.

So I would suggest you get a range of resistors from perhaps 10 KOhms to 100 KOhms in steps of 10 KOhms and try them one at a time starting from low to high. See if the light goes out. The lowest possible.

Be careful though. Make sure you check the heat of the resistor. Resistors come in different power ratings I think 0.5 watts should be ok. But if it gets too hot you need to increase the power rating.

That's what I would do anyway.

I should have been more specific. When the low coolant level sensor is fitted into the expansion tank, and the plug is disconnected, then the low coolant level lamp stays on solid.

 

[74123]

Your testing may have achieved the results you posted. So why is it when you remove the sensor from the bottom of the bottle no coolant runs out? Nor does it have any seal at the bottom.
Because it never makes contact with water (coolant). There is a float inside the tank. It interfaces (through the plastic) to the sensor that goes inside a sealed chamber of the bottom of the expansion tank.

Here's a E39 tank with the same engine. (cut in half)

https://www.bimmerfest.com/forums/showthread.php?t=505142

I can't see all the way inside the ET but I can see that the sensor is inside a small housing of sorts. The hole is a small hole. About 8mm diameter. If you get a bottle, drill an 8 mm hole in the cap, fill it full of water and turn it up side down does the water pour out? Or does it stay in there? Air has to get into te bottle to replace the water in order for water to come out. Try it. I don't think it will pour out. I think the hole is too small. But I'll let you do that experiment.

 

[74123]

With it disconnected, the low coolant level lamps stays on solid.

I have just realized that you are not the OP. My response was written on the assumption that you were. But, it really doesn't make any difference because if you wanted to leave it disconnected and turn the light off I reckon the same technique could apply to you.

 

[IceWhite]

I have just realized that you are not the OP. My response was written on the assumption that you were. But, it really doesn't make any difference because if you wanted to leave it disconnected and turn the light off I reckon the same technique could apply to you.

Ahh, ok.

Just curious, how do you explain a light off situation first thing in the morning when the car is still cold?

 

[74123]

Ahh, ok.

Just curious, how do you explain a light off situation first thing in the morning when the car is still cold?

Perhaps the computer has something to do with that.

 

[MrMCar]

Just curious, how do you explain a light off situation first thing in the morning when the car is still cold?

I assume you mean the all too common first thing in the morning low coolant level?
4 common issues cause this:
1) Cold overnight conditions contract the coolant and the level dips down just enough to turn the light on. (VERY common)
2) Sensor is starting to fail.
3) Float inside tank is going bad and/or restricted.
4) Connection inside plug has been fiddled with too aggressively and has a poor connection when cold.

 

[Overboost]

I don't get the argument here? THERE IS NO COOLANT ON THE COOLANT LEVEL SENSOR.

The low coolant light is triggered by the float in the liquid side of the expansion tank. The float has a magnet in it. The switch is inside the bottom of the probe mounted outside of the liquid chamber. Its called a "reed switch". it is normally open. When the float/magnet drops it closes the switch and triggers the warning on the OBC.

 

[LL i am]

jmo69 and Overboost are correct.
sensor do not touch coolant
sensor can be out and no coolant drains
sensor senses the magnet inside attached to the float