Thread: Low coolant alarm

I have a float switch in mine, too.

Yeah saw yours Ron, motivated me to do mine. I think its easier to copy the BMW system than to try and put a sideways one in though, less danger of leaks

Whats an MM plumbing fitting?

Originally Posted by ytt105

Whats an MM plumbing fitting?

male-to-male - one end screwed into the hole you make and the other end to screw a cap on to.

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Here's one end sticking out. The BMW tanks have a molded plastic thread sticking out here

I have been putting this off for to long so when all else is done this will be next on the list. Can you elaborate, the 26mm m to m fitting does the BMW sender screw directly onto it and seal? You chose to use the 109mm sender, how far down does it go and do you think one of the shorter 95mm ones would stay shut / off at normal coolant level. Where did you get a new sender for $10.

Originally Posted by wayneg

Can you elaborate, the 26mm m to m fitting does the BMW sender screw directly onto it and seal? You chose to use the 109mm sender, how far down does it go and do you think one of the shorter 95mm ones would stay shut / off at normal coolant level. Where did you get a new sender for $10.

All good questions. The brass male/male fitting was just a standard plumbing fitting from Bunnings, its just a thread on each end with a hole in the middle - the brass one looked like a good fit although I had to ream it out with a file very slightly as the float switch was fractionally too tight for the hole - there might be something around that's a more perfect fit but I didn't find it. The BMW float switch has a lip at the top, so the sender unit just 'drops' into the hole until the lip hits the top which has a rubber washer on it. It's then screwed down tight with the aid of a collet/collar. The float switch came with its own collet which I discarded as the thread on it was odd and I couldn't find anything to match it so made my own out of a plastic end cap. The plastic end cap is also from Bunnings and a standard plumbing fitting - I just drilled a hole in it to turn it into a collet with the top of the float switch sticking out.

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95mm BMW float switch (round pins) with the collet it came with to the left, just drops into hole then screw it tight. I used the longer switch with flat pins

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Float switch with collet on, plastic m/m fitting to left - hole was too small in the plastic one for the switch to fit through it so used a brass one with a bigger hole.


When fitted to a BMW the 95mm one sits very low in the tank due to it's mounting position and the slightly different design of the BMW expansion tank. The tank would have to be pretty empty for it to activate the switch. I figured they knew what they were doing, as my brass fitting sticks up some what more than the standard BMW setup, I opted for the longer float which probably ends up sitting at about the 1/4 mark (1/2 full mark would be about the standard fill point when cold), still higher than a 95mm in a BMW would sit though. The 95mm would probably still stay shut at normal coolant level but might activate from sloshing etc /shrug

I bought my BMW float switch on eBay for $10.75aud+ $6 p&p from USA - took 5 days to arrive

BMW Coolant Level Sensor E28 E30 325 528 7151: eBay Motors (item 290289527726 end time Oct-07-10 10:12:16 PDT)

edit: with the wiring make sure you either use a resistor or a relay with built in resistor (about 80ohms) - I killed my first sensor (the 95mm one) by accidentally putting too much current through it.

Finally put in a low coolant alarm. I had got together the bits for the BMW type float ages ago. While I was playing with it on the bench sorting out the relay connections I managed to Fry it.
Plan B... I had a float level sensor from e-bay cost $1.75 and a pair of Flashing leds in housings $4 the pair.
I placed the led`s one each side of the cluster bezel. Fitted the float into the expansion tank through the cap hole and stuck it to the bottom of the tank. Drilled a 2mm hole in the side of the tank to get the wires out then sealed with epoxy underwater sealant on the inside and out. I ran a live from the cigar lighter + feed, through both led`s then to the float. The second float wire to earth. No need for relays as the sensor is OFF when floating and ON when not, unlike the BMW type sensor. If the level drops I get 2 bright red led`s flashing which I would be blind to miss. Cost about $8.



[ame=http://www.youtube.com/watch?v=2XHsm3x7mkY&feature=mfu_in_order&list=UL]p38 low coolant warning - YouTube[/ame]