Thermostat question

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Inferno
Joined: Sun 30 Sep, 2012 08:35
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  Z3 roadster 1.8
Location: Athens
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Thermostat question

Post by Inferno » Tue 01 Sep, 2015 16:27

I changed my thermostat about an hour ago because the old one had stuck open, the temp needle doesn't sit exactly in the center it is about 1-2mm to the left (colder). Does anybody knows why?

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Dino D
Joined: Fri 10 Feb, 2012 16:59
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  Z3 roadster 2.8

Re: Thermostat question

Post by Dino D » Tue 01 Sep, 2015 16:51

Will dig up a thread that explains the gauge behaviour and the dash test so you can see the actual temp reading (the gauge only shows a range, not actual).

Dino D
Joined: Fri 10 Feb, 2012 16:59
Posts: 376

  Z3 roadster 2.8

Re: Thermostat question

Post by Dino D » Tue 01 Sep, 2015 16:53

Here you go, hope not helps, very interesting test to run to see your actual temps:
http://www.zroadster.net/forum/viewtopi ... =5&t=37703

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Inferno
Joined: Sun 30 Sep, 2012 08:35
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  Z3 roadster 1.8
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Re: Thermostat question

Post by Inferno » Tue 01 Sep, 2015 17:01

thanks, i will try that later tonight!
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Inferno
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  Z3 roadster 1.8
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Re: Thermostat question

Post by Inferno » Tue 01 Sep, 2015 22:00

top code i saw was 2f, and the needle a bit to the left as the pic i posted above, so if i understand correctly i don't have a faulty gauge. new thermostat is mahle-behr and opens at 95c. is this how this particular thermostat works or something else?
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therealdb1
Joined: Tue 25 Jun, 2013 22:47
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  Z3 roadster 2.0

Re: Thermostat question

Post by therealdb1 » Tue 01 Sep, 2015 23:21

It's like that because that's the way it is.
You cannot expect a temperature gauge to sit exactly in the middle of full scale and it will generally move slightly up or down depending on several things e.g. engine load, ambient temperature, airflow around the engine. The gauge is measuring the temperature of that huge block of metal and the oil and the water at a single point where the sensor is located so it is only an estimate of what is going on under the bonnet anyway.
If the gauge indicates around about the middle that is normal operation. Don't start worrying until it is significantly near the blue or even more so the red.
However the link describing how to get an actual temperature from a hex code is interesting.

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Inferno
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  Z3 roadster 1.8
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Re: Thermostat question

Post by Inferno » Wed 02 Sep, 2015 00:04

Happy to hear that.
In my E36 sits always in the middle no matter what, same story in my Z3 before the replacement that's why i thought it might be a problem.

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Southernboy
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  Z3 roadster 3.0i
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Re: Thermostat question

Post by Southernboy » Wed 02 Sep, 2015 05:29

The temperature is taken by a sensor attached to the top of the radiator (left side if you are facing the engine) Perhaps the sensor is faulty ?
"Normal is overrated"
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Dino D
Joined: Fri 10 Feb, 2012 16:59
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  Z3 roadster 2.8

Re: Thermostat question

Post by Dino D » Wed 02 Sep, 2015 08:34

Southernboy wrote:The temperature is taken by a sensor attached to the top of the radiator (left side if you are facing the engine) Perhaps the sensor is faulty ?
Hi Barry,
Having replaced both temprature sensors on my 2.8 I can confirm that sensor on the side of radiator is actually the auxillary (electric) fan temp switch. I believe it is the case in the 1.9 too as I have fitted the switch from a 1.9 to my 2.8 (the 1.9 kicks the fan on at 80/88c low/high speed if the water temp leaving the radiator exceeds those limits. The standard 2.8 one is 90/99c).

The sensor giving the readout to the dash is located in the head on the intake manifold side (visible and accessible without removing the manifold). I am not sure on the 1.9 where it is but would assume it's also on the engine somewhere rather than the radiatior?

Since changing my temp sensor that gives the dash readout (and bleeding the system) my readouts are a bit lower but I'll still get a peak reading of 2F (113c) under heavy load or say in traffic. Of course the gauge is rock steady in the middle. However others get readings of max 99c so I'm trying to work out why that is.
I suspect there is still air as the 2.8 system is not a self bleed system and seems to need a few attempts..not sure on the 1.9.

therealdb1
Joined: Tue 25 Jun, 2013 22:47
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  Z3 roadster 2.0

Re: Thermostat question

Post by therealdb1 » Wed 02 Sep, 2015 09:35

As I said the temperature is being measured at one point in the cylinder head, not the radiator as that temperature will fluctuate every time you stop or move or the fan cuts in.
"Cool" water is being pumped into a "hot" engine through narrow ducts there will be all sorts of temperature gradients and possibly differences in temperature of several degrees at various locations around the system.
Temperature gauges are not calibrated and even the thermostats are designed to open at nominal temperatures not an exact figure. The cooling system is not a miracle worker and the indicated temperature will vary depending upon operating conditions.
If the gauge is somewhere around the middle under normal driving conditions don't worry and be happy! :)
Only start to panic when the gauge is at either of the extremes.

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