I'm the proud new owner of a really nice white 85 635csi I picked up today. I'm reading the forums and linked manuals but maybe someone can answer before I find it. : )
The coolant temp gauge on the dash is not working and I'm anxious to fix it so I can drive the car with confidence . The top of the thermostat housing has 3 or 4 sensors , one of which I'm assuming is the coolant sensor. Am I on the right track and which one is it ?
Thanks !
Have a look at the attached photo. The coolant temp sender that communicates with the on dash coolant temp indicater gauge is the two spade jobbie (unconnected in my photo) on the left.
The sender is comprised of two components:
1) a thermistor (the fat spade) wired to the temp gauge whose resistance will vary depending on coolant temp and so provide an analogue signal to the needle.
2) a high temp switch (the narrow spade) that will close if the temp coolant temperature reaches 243 F (Defcon 1 !! ) and will illuminate the dash idiot light.
Assuming here that your dash gauge needle is inert and stone dead then you can start to pinpoint the problem very easily. With the key in accessory position pull the connector off the fat spade and ground it to the water manifold. If the gauge needle pegs right then both the gauge and wiring to it are fine and the sender is pooched. If still no needle movement then either the wiring to the gauge is breached or the gauge itself is no good. The same test applies to checking the idiot light .
It would be best if you did not refer to this sender as a 'sensor' because the Coolant Temp Sensor (aka CTS and the baby blue one on the right in the pic) is quite a different animal and serves the top important function of relaying coolant temp info to the Motronic computer so that fuel can be appropriately metered to the injectors.
Ignore the cobalt blue sender with the black line running from it on the left of the photo as this is something I added . You will have in its place the stock charcoal cannister purge valve switch with two small vacuum lines runing to/from it.
The brown plug is the Thermo Time Switch (aka TTS) that controls when to activate the cold start valve. There is another sender on the end of the cylinder head right beside the water manifold. It controls the flux capacitors and should under no circumstances be messed around with.
Hope this helps and welcome aboard.
if your testing indicates a bad gauge, try cleaning the ground on the gauge (to the circuit board) and putting a slight bend in the threaded rod to make sure it's making good contact. had issues with both my tempand fuel gauges since this type of ground is a terrible design.
Wow thanks for the help. The small spade turns the idiot light on when grounded, the fatter spade only makes the temp needle twitch . It jumps a little but there is no real movement left to right.
Does this mean I'm pulling the cluster next? I really don't like driving any car without a functioning temp gauge. How hard is it to get the cluster out ?
Last edited by tbsbimmer; 05-14-2011 at 02:21 PM. Reason: added question
It's not very hard at all. Just a few screws and it pops right out really.
Here is how to remove the cluster, with pics:
http://www.z3bimmer.com/OffTopic/E24Bimmer//OdoGear/
Are the "SI" (Service Indicator) lights working? Any other gauges not working in the cluster? The Temp gauge goes through the SI processor, so if it is bad (Batteries dead or leaked on the circuit board) it may affect the temp gauge.
Thanks for the link, the SI lights are working , at least the yellow and 2 red ones to the right.
Ahh, those need to be reset, and if they don't reset, the batteries may be bad and the SI board could be your problem.
The green SI lights should come on when the key is first turned, all of them when first reset and then fewer and fewer as the time for service nears. When the cars starts the SI lights should go out.
When service is required, the yellow light comes on and stays on, along with an "Oil or "Service" light. If the SI lights are not reset, first one red light and then another comes on and stays on.
Resetting the SI lights:
http://bigcoupe.com/phpBB2/viewtopic.php?t=1669
Make sure you do the reset that corresponds with which "Oil or "Service" light is lit up.
Last edited by CW6er; 05-15-2011 at 01:07 PM.
I swapped in a used cluster today and the coolant gauge works now : ) as an added bonus so does the odometer
My coolant temp gauge does not work. When i turn the ignition it moves a little bit. Im after a full restoration everything was taken apart. I wanted to torque the head bolts after the engine warmed up and i saw the temp gauge not moving. The head cover was hot. I grounded the connectors but no luck. Only the idiot light worked. I took the speedo apart but saw no strange things.
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