MyE28.com

Hey all...

Took my intake manifold off and found that I have a broken sensor that has 2 prongs and screws into the side of the cylinder head ... It's some sort of coolant sensor.. it almost looks like the fan switch sensors if you know what I mean......

I CANNOT FIND anything on this ....

That sounds like a coolant temp switch that lights the over temp signal on the coolant gauge? I have one on my M6 (in the coolant manifold) but have never seen one on an e28. All e28's have a provision in the cluster for an over temp 'idiot' light but it was never used to my knowledge. It would work just like the low fuel light on the gas gauge. Newer cars began using a combination switch/gauge for the same things. Perhaps a PO adapted this from a different BMW ?

That would make sense because my coolant light was on but the temp was fine... Idk what to do to replace it... It's pretty broke and I'm thinking that's where my coolant leak is coming from..

P.s this car has a very unknown history... But it's sad and I'm saving it lmfao

I have pictures idk how to upload them

Which one? There are several.

on a Lincoln the one back at #6 is tied into the HVAC to keep the blower off when the coolant is cold. I don't think BMW does this but I have no idea what might be in that spot, if anything.
The one forward of that, roughly at the #4 cyl is the cold start advance solenoid switch
one forward of that is for the EGR system temp switch
The front-most one where the upper rad hose connects is for the glow plugs and temperature gauge or idiot light. I think BMW uses the switch part to turn on the fan, Lincoln just tells you that you're screwed with a nice pleasant red glowing light of doom. You may or may not also get the idiot light, I have no idea.

gadget73 wrote: Jun 30, 2021 10:25 AM Which one? There are several.

on a Lincoln the one back at #6 is tied into the HVAC to keep the blower off when the coolant is cold. I don't think BMW does this but I have no idea what might be in that spot, if anything.
The one forward of that, roughly at the #4 cyl is the cold start advance solenoid switch
one forward of that is for the EGR system temp switch
The front-most one where the upper rad hose connects is for the glow plugs and temperature gauge or idiot light. I think BMW uses the switch part to turn on the fan, Lincoln just tells you that you're screwed with a nice pleasant red glowing light of doom. You may or may not also get the idiot light, I have no idea.

So it's right at cylinder 4 right below the intake bore.... Would you happen to have the part number?? I cannot find anything ... Fyi the whole head snapped off.. I'm guessing it was badly cracked for some time..

I *think* thats the 17 degree switch. If it is, 12631279721

https://www.realoem.com/bmw/enUS/showpa ... Id=12_1289

should be the link to all of those things, unfortunately it doesn't really show their physical location in the cylinder head.

The only thing that does is bump the timing below 17c for easier cold starts.

I totally missed that we were talking about a td for which I have almost no experience. So a temp switch nonetheless but not for a coolant idiot light as I tried to describe.

When you said your coolant light is always on even though the temp is fine I believe you are talking about the reservoir/expansion tank sensor that lights the check panel and not a light on the temp gauge. That is a low level sensor but the sensor itself has often gone bad simply due to age.

fwiw I think it is a good idea to have an idiot light for temp just as we have a idiot light for low fuel warning and low oil press. Most drivers only look at the speedometer and may not know what the other gauges mean. High temp is bad situation on these cars and BMW provisioned for it but didn't use it ?

if there is provision for that light but no connection, you should be able to wire that into the switch part of the front-most sensor. Confirm in the wiring manual but I'm pretty sure that kicks the electric fan on if the temperature hits a certain point. Would be nothing to also make it turn the warning lamp on as well. When I added an oil pressure gauge to my Towncar I modified the fittings so I have both the gauge sender and the idiot light switch. The red light is a little more in my line of vision than the oil pressure gauge is.

I have the opposite condition, the switch turns on a light but nothing else. On the to-do list is make it turn the fan on. Also simple, just have mount a relay somewhere and run a bit of wire. I just need to figure out where I can cleanly tap into that circuit so it doesn't look like a hack job.