Coolant level sensor?
 

Is there one somwhere that tells me that the coolant level is low?

Nope, unless you have that option. The plug in the expansion tank replaced the low coolant sensor. That would be a good thing to have BTW.

I see the plug with a big C clip. What do I need and where do I get the coolant level option? How much new/used? Is it a float/reed switch gizmo or does it measure resistance?

Let's say I have a hypothetical slow coolant leak and I don't have a level sensor and I do not see coolant on the ground, what are the first signs and is it too late i.e. engine damage?

Where to get it and hook it up? That I do not know.

How slow of a coolant leak? I pop the hood on my car every time I fuel up, and do a visual. I had a slow leak, that soon turned to a part time drool. Water pump time for me. Keep checking guages and check the oil for the milkshake look.

The 126's I have looked at have a sensor in the side of the expansion tank. Is that not true of the 300D? The one I am most familiar with is a 1990 420SEL, not a deisel.

AFAIK, the 126 has the sensor but not the 123. Don't think it was an option either.

I'd have to look, but I'm almost certain this was an '86+ thing for MB. I can swear my SD does not have it, yet the SDL does 100% for sure.

None of my cars has that.

would this fit?
 

http://www.***************/search/product.aspx?sid=1teezt450axfdt55g05tfr45&makeid=800016@Mercedes&modelid=1195545@E300D&year=1996&cid =16@Cooling%20System&gid=2184@Coolant%20Level%20Sensor

Would this fit in the expansion tank hole after the plug retained by a C-clip is removed? Does anyone know what type of sensor it is?

Are you saying the one on the link I posted is the wrong one and the link you posted is the right one? Difference in price is 3 to 1.

Lance,

What year and model is the coolant level sensor link you posted from? Will it fit an 83 300D expansion tank?

I really want a coolant level sensor since it is the first line of defense against overheating the engine. If I have to make my own, I will.

I need to correct myself, there is a plug on the expansion tank, yet none of the 123's I've seen has it hooked up.

OK as far as I can tell from online searches, this level sensor

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2291DK2BB2320WOD0D&year=1985&make=MB&model=380-SE-001&category=All&part=Coolant+Level+Sensor

is from an 87 SDL. Does anyone know if an 87 SDL uses the same expansion tank as the 83 300D's? If so, I may be in luck. Looks like it has a float on a lever arm and with a magnet and a reed switch.

Here's the expansion tank plug from 83 300D

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1Q81CPNVK2330S0STI&year=1983&make=MB&model=300-DT-001&category=G&part=Expan.+Tank+Plug+Kit

which looks like it has the same mount as the 87 300SDL coolant level sensor. [http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2291DK2BB2320WOD0D&year=1985&make=MB&model=380-SE-001&category=All&part=Coolant+Level+Sensor

Can someone confirm? I want to order one but would hate to get the wrong one.