Thermostat not opening? Bad sensors?

[jaredmac11]

I want to preface this thread by saying this is an E21 M42 swap. There could be a few issues here and I dont think they are linked but I want to make sure. The car runs flawlessly, except the following:

1) I dont think the thermostat is opening. I replaced it a year back and the engine sat as I worked on other pieces of the car, but its essentially brand new. The lower coolant hose is cool to touch and the upper hose is warm/hot but not super hot after a few minutes of idle.

2) the Temp gauge is not working. This could be my wiring though its fairly straightforward. All my other wiring was correct and this is the same wire color across platform... seemed like a slam dunk. I think its the temp sensor to cluster (inner-most sensor). I know yall cant help with non-factory wiring but what impacts would bad sensors have outside of no temp gauge? would a blocked thermostat impede the sensor from getting a reading?

3) If the ECU Temp sensor (outer-most) is not working as well, what will it do to the ECU?

Obviously getting the temp sorted is key, Im just curious if these are some-how connected; if Im overly cautious about engine temps and not letting it idle enough; or if I have a bum thermostat and bum sensors? My wiring could be off too so I will confirm that soon.

Going to pull the thermostat soon, just being lazy since I dont wanna order new gaskets and crap.

[jaredmac11]

thermostat was fine.

I had thought I bought new sensors, but I went through receipts and couldnt find one confirming I did. So I bought 2 new sensors and the gauge works now.

That was a huge pain in the ass to change with the intake and coolant piping. never again.

[dcig]

thermostat was fine.

I had thought I bought new sensors, but I went through receipts and couldnt find one confirming I did. So I bought 2 new sensors and the gauge works now.

That was a huge pain in the ass to change with the intake and coolant piping. never again.

How did you test the thermostat? I just took mine out and tested in a pan boiling some water. But it looks like mine didn't open, but I think my gauges were fine before hand.

I'm at the point of replacing most items cause I have the whole engine bay ripped apart at the moment lol

[jaredmac11]

I did it the lazy way to avoid replacing the gasket.

Without the sensor it was hard to tell, so what I did was buy an IR thermometer and waited til the thermostat housing hit close to 88 degrees then I noted the coolant level dropped and the lower radiator hose started to warm up.

You have an open system if both rad hoses are hot. You have a closed system if only the upper rad hose is hot.

If you have it in a pot of water and you're reaching the right temp, you have a bad thermostat.


edit: What symptoms are you seeing? The front-most temp sensor is for ECU. Innermost is for the gauge. If the sensor for the gauge is faulty it shouldnt read at all. If you are getting intermittent readings or a bouncy needle, it could be air in the system. If the thermostat isnt opening, you're going to have a high temperature reading pretty quick.