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  #1  
Old 01-07-2019, 11:49 AM
cigar1 cigar1 is offline
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Thermostat refuses to open on 2005 X3 3.0

I have a 2005 X3 3.0 with an overheating problem. The Thermostat remains stuck closed and the engine overheats after 5 minute warn up. I replaced the Coolant Temperature sensor in the lower radiator hose but the problem appears to be the lack of 12 volts DC at the thermostat heater connector at the thermostat housing. The voltage does not register more than .5 volts DC at the wire plug which connects to the thermostat so the thermostat will never open because the wax/gell does not heat up to allow the thermostat to pop open. Resistance across the thermostat heater element is 12 ohms which would draw 1 ampere current if voltage was present. I thought the new sensor would tell the computer to send 12 volts to the thermostat but replacing it did not change anything. The other temperature sensor by intake manifold appears to work as the instrument gauge registers normal cold and normal temperature at 12:00 o'clock position before heating up. The fan works when calling for A/C but if the A/C is turned off; the fan will not turn on even when the temperature gauge is heading to the red. If the thermostat heater was getting 12 volts and it did not open...then I would replace the thermostat, but indications are that an electrical signal is not telling the fan to turn on or the thermostat to open. Generic code reader did not set any codes. Don't have a good one. I am not a mechanic but can usually figure out simple things. This one has me stumped. Not sure if the temperature sensor at the heater core has any effect on this but I can tell you that the heater does not work either (possibly from the thermostat stuck closed). Can anyone point me in the right direction?

Thank you in advance
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  #2  
Old 01-07-2019, 12:11 PM
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Doug Huffman Doug Huffman is online now
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It is a wax motor not dependent on ECU mapped current for heat to open. The thermostat may indeed be stuck shut but it is not an electrical/ECU problem.
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Old 01-07-2019, 01:30 PM
cigar1 cigar1 is offline
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Thermostat refuses to open on X3 3.0

I want to thank Doug Huffman for his quick replay, however I do not understand what the term wax motor refers to unless the analogy refers to the wax melting which causes expansion thereby pushing the stem out with the the valve at the end which allows coolant water across the thermostat housing and if that be the case - it does require some electrical input from somewhere. There is an electrical plug attached to the front of the thermostat housing which causes the thermostat to open. The problem is no 12volt DC at the heater terminals of the thermostat. When there is 12 Volts present, the heater causes the wax to melt releasing the thermostat. When 12 volts is not present; the spring in the thermostat housing pushes the valve closed (shutting off coolant water across the thermostat housing). So, yes the thermostat is stuck closed but it is supposed to be closed when engine is cold and for sure when there is no voltage at the heater terminals of the thermostat heater element. If I can get 12 volts to the thermostat housing, I think it will be the fix. I have an E46 and when I check that thermostat, I have 12 volts at the terminals of the thermostat housing and that thermostat is not stuck closed and the fan works. Something controls the fan and thermostat simultaneously, I just cannot figure out what that mechanism is. I "think" the temperature sensor by the firewall on the block sends info to the instrument gauge and DME, but it appears to be working as the gauge registers in what appears to be norman fashion.

Also, the fan works with A/C "on" but refuses to turn on even when the temperature gauge is right next to the red mark at about 3:00 o'close position on the temperature gauge. I have replaced the coolant temperature sensor (today) in the lower radiator hose.

I sincerely hope this clarifies things a bit.
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Old 01-07-2019, 01:34 PM
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TL;DR

The electrics allow your ECU to open the thermostat earlier or farther than coolant temperature. Other than that it is conventional wax motor thermostat that opens in response to engine coolant temperature. Study "mapped thermostat".
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Scepticism is the chastity of the intellect, and it is shameful to surrender it too soon or to the first comer: there is nobility in preserving it coolly and proudly through long youth, until at last, in the ripeness of instinct and discretion, it can be safely exchanged for fidelity and happiness.
(The Works of George Santayana p. 65)

Eschew eristical argumentation. I am responsible for what I write, not for your understanding of it.
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Old 01-07-2019, 02:04 PM
cigar1 cigar1 is offline
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Thermostat refuses to open on 2005 X3 3.0

Again, I wish to thank Doug Huffman for quick response and took his advice to research "mapped thermostats". Am posting part of the article that explains the operation and if I understand it correctly, it still relies on the ECU for proper operation and not just engine temperature:

The design of the characteristic map thermostat is similar to that of a traditional wax thermostat. In a traditional wax thermostat, the wax is heated by engine coolant, at a specific temperature the thermostat opens, allowing coolant to circulate and maintain engine temperature. The main difference with a characteristic MAP thermostat, is the DME now has influence on the opening of the thermostat. Using an electronic heater to heat the wax element, opening the thermostat as needed.

So to reiterate, I have a "MAP thermostat" which has an electronic heater to heat the wax element. The problem is no electrical power at the wiring harness connected to the electronic heater which is inside the thermostat housing. According to the article, that signal is controlled by the DME. The coolant temperature does not control the opening and closing of this thermostat.

Can someone help me figure out which sensor is not telling the ECU to send 12 volts DC to the electronic heater? The same circuit controls the electric fan which doesn't work either unless I turn the A/C on.......then it kicks on.

The computer thinks the coolant temperature is cold enough to not heat up the wax or turn the electric fan on......and it keeps thinking this right up to engine overheat. Coolant temperature sensor was replaced by me today.
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Old 01-07-2019, 06:46 PM
cigar1 cigar1 is offline
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Thermostat refuses to open on 2005 X3 3.0

To Doug Huffman:

Yes, you are right! After hours of research, I have learned that the thermostat mostly operates as a wax motor (must be a nuclear term), and that the electronic heater control only activates under very precise and complicated conditions (one being under heavy load going in excess of 100 miles per hour). And even then it just opens a bit more, say for emergency cooling.

So I guess it is a wax motor with electronic assist booster.

Anyway, I believe the coolant temperature sensor (in the lower radiator hose) did not get hot enough to kick on the radiator fan because there was no hot coolant circulating through it.

I suspect a jammed shut thermostat or a water pump impeller is not impelling any hot coolant through it.

Either way, I am done working on this for my friend and he will be having it towed to a real mechanic.


But I learned a lot and I thank you for your succinct input.
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