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#1 (permalink) Old 01-07-2012, 12:17 AM
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High engine Temp via hidden OBD

i have a high temperature in my car as well, i don't get the overheating message but when i see the temp via hidden OBD it going between 90 deg to 105 deg but when i open the heater with the highest temp, the engine temp go down to 77 deg, so i don't know if the problem is from the temperature sensor or from the thermostat or from something else??? the fan also is not working when the temp go high.
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#2 (permalink) Old 01-07-2012, 11:51 AM
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Thats your problem - the fan should kick-in and draw the temp back to 90ish... 105 is above boiling point !!!
Get a live to the fan to test that it works without issues, if it does work ok then it is a temp sensor fault...
On many BMW's there are two temp sensors, one on the head and one on the rad to activate the fan !


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Last edited by Jack Dabsy; 01-07-2012 at 11:54 AM.
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#3 (permalink) Old 01-08-2012, 01:18 AM
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you right i have tow temp sensors in my car (2007 BMW 530i N52), i tried to replace the one located in the engine head but i still have the problem, the fan is working while the this sensor been disconnected on highest speed, but i have to try to replace the second temp sensor located in the hose inlet to radiator (it is also called fan switch) maybe the problem from it, what you think?? or the problem is bad thermostat?
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#4 (permalink) Old 01-08-2012, 07:29 AM
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Go for the fan sensor/switch...
If your bottom hose is mucho cool then that will be the thermostat/pump...


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#5 (permalink) Old 01-08-2012, 11:33 AM
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The way they design thermostat's these day's are to fail in the open position. I would double check what kind you have before you go ripping it out. If it fails in the open position then i would suspect the thermostat last. A few questions.

1. How dose the car warm up? normal? really slow?

2. Does your car have high temps when cruising on the freeway or is it normal temps?

3. Does your car over heat only when driving around town?

4. Have you checked your coolant level?

You say the fan still works when you disconnected the sensor? Okay great this still dosen't mean that the sensor is bad. They could have designed the system as a safety measure if the PCM loses a signal from the sensor it will automatically turn on the fan. But then....the mil light would turn on.

5. Have you checked your relay's?

Normally when something does not come on when it supposed to you have a open or high resistance somewhere in the circuit. I would check the fuse first. then the relay. Print out a wire diagram and follow the path of current. Find out where and open somewhere could cause a fan not to come on. Test to see if voltage is getting to your fan. If you notice that not enough voltage is getting to your fan. Then you need to find out where the high resistance is. Check for voltage drops. If you have no voltage going to your fan. Then you have a open. *Remember to always check for good power and ground in a circuit first.

If everything is healthy then I would start to test your sensors to see if they are bad. (notice i said test them not replace them....test them first).

Last edited by rivroshaun951; 01-08-2012 at 11:36 AM. Reason: Oops basics first.
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#6 (permalink) Old 01-09-2012, 04:52 AM
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thanks rivroshaun951 for your reply and your explanation, here is the answers for your questions:
1- i feel the car warming up little slow, it took about 10 min to reach 75 C.
2- the car has high temp in both of city drive and highway drive. Note that i am not getting the overheat message on idrive, its only on the hidden OBD menu.
3- as mentioned above.
4- the coolant level is ok.

yes the fan is working on highest speed when i disconnect the temp sensor located in the engine head so i don't think there is a problem with the fan electrical connections.
yesterday i checked the pipe hose inlet to radiator and it was cold while the engine temp is over 95 C, i still didn't check the temp sensor located on this pipe... So what you think, should i check it or the reason is from the thermostat???

5- i didn't check the fuses and relays because i already connect the car to code scanner and i didn't get any fault code, if there is any fuse or relays problem;for sure i would get fault codes right??
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#7 (permalink) Old 01-09-2012, 11:08 AM
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I am not a professional. This is just my opinion I could be wrong.

AHHHHH!!! you see grasshopper just like the men who created them. Computers can be lied to. Computers can be confused. computers can fail.

It is not a certain thing that a fuse or relay would cause a fault code. For example. a burnt fuse could still possibly allow current to run through it. It could have just enough resistance to prevent the fan from running and still not cause any fault codes. That's if the manufacture designed the system to work that way. When you are trying to solve a diagnostic problem such as this. Don't forget the basics. Check the Fuse and Relay's. Make sure they have the correct amount of voltage going in and out across them. make sure the relay is not sticking. I highly advise you print out a Wirering diagram. It's your road map. Without it you could get lost. Check for power and ground. You will kick your self in the butt someday if you don't make these basic fundamentals part of your routine every single time.

As far as the fan goes. Okay great it works fine so now.....whoa whoa whoa....

You said you were getting this information from your hidden OBD. Does this hidden OBD take the same temp reading from your idrive? What I mean to say is. Maybe the hidden OBD is taking the temp from some other sensor. OR it might even be calculating temperature instead of getting you an acutal engine coolant temp like idrive (or vice versa). Maybe it's not actually engine coolant temp coming out off the engine. Who knows. Sometimes computers are just funky like that and nothing is really wrong. Bottom line is your car overheating. Or is this hidden OBD thing just saying your running hot.

One other thing. if I read it right. the hose was cold going out of engine and going into the radiator (normally big hose on top of radiator). If this is what you found then I would believe the car would be running very hot to over heating. This means your thermostat is stuck closed and no coolant is flowing. Your idrive should have picked this up no problem. unless something is wrong with your idrive or........ a sensor.
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#8 (permalink) Old 01-10-2012, 02:51 PM
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Like I said Lol


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#9 (permalink) Old 01-13-2012, 01:15 AM
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Is it actually boiling? If not what is the worry?

I copied this below from elsewhere

"The temperature of the coolant can sometimes reach 250 to 275 F (121 to 135 C). The cooling system uses pressure to further raise the boiling point of the coolant. Most cars have a pressure limit of 14 to 15 pounds per square inch (psi), which raises the boiling point another 45 F (25 C) so the coolant can withstand the high temperatures."

The article suggests that 50/50 coolant/water boils at about 106C at 1 atmosphere sea level, but under pressure could go to 131 before boiling depending on the cap rating..

So could it be a faulty radiator cap?

Thermostat will open at about 85C so its possible that the hose is still a little cool when the temp is indicating 95.

How accurate is the temp gauge? Have a look at this link

Catalog

Basically if there is no steam coming out, the coolant level is not dropping, there are no bubbles in the radiator and there are no other issues, are we worrying about nothing? (Maybe the hidden OBD is hidden for a reason?)

Oh and don't forget the fan will run if the a/c is on too.
And of course the temp will drop if you turn on the heater. It is actually another radiator.
(I have at times used the heater on a hot day with all the windows open to stop a sick car from boiling)

Also like Dabsy said.

And rivroshaun951said
"Bottom line is your car overheating. Or is this hidden OBD thing just saying your running hot."

My daily is a Mitsubishi HSGR (but I wouldn't mind an e34 525i)
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