Temerpature gauge goes straight to max

Hi,

I changed a top gasket set on my L322 BMW V8 and the car actually started and ran!!

However......my temperature gauge went straight to max. I came across this thread

http://www.landyzone.co.uk/lz/f10/l322-4-4-temp-gauge-over-read-help-126636.html

,which has the same problems, I've contacted the gent who posted, does anyone have any ideas?

1) If it is electrical, how do I test it / check it?
2) I changed the thermostat as a matter of course (90,000 miles)

Charlie

been a lot of problems with new thermostat replacements recently view recent threads but sounds like a plug/wiring issue to me

wil2813 said:

been a lot of problems with new thermostat replacements recently view recent threads but sounds like a plug/wiring issue to me

Click to expand...

+1, have you trapped a wire during all your recent work, sounds if it's shorting to earth

Frankly I could have messed anything up - amazed it started first time.

Tom / Will, I agree it is most likely wiring. How would I go about diagnosing it (sorry if this is basic...)?

Charlie

if it helps,i had a rover 25 td a few years ago,i broke down and the temp guage shot round to max,i traced it to a broken earth cable,put a new one on -back to normal.

p.s. temp sensor to the wire case on top of the injectors is a pretty straight run...

td5nut said:

if it helps,i had a rover 25 td a few years ago,i broke down and the temp guage shot round to max,i traced it to a broken earth cable,put a new one on -back to normal.

Click to expand...

That's a point, have you reconnected everything you disconnected. It's Alan not Tom by the way.

funny things them old rovers friend had 1 years ago think it was a 620td or summit went in limp one day after loads of head scratching it ended up being a blown brake light bulb changed it everything good again

wil2813 said:

funny things them old rovers friend had 1 years ago think it was a 620td or summit went in limp one day after loads of head scratching it ended up being a blown brake light bulb changed it everything good again

Click to expand...

bluddy`ell,wot drewyer to a brake light bulb mucker?

I'll change my brake bulbs tomorrow, been limp for years.

tomcat59alan said:

That's a point, have you reconnected everything you disconnected. It's Alan not Tom by the way.

Click to expand...

Tom, yes all wires connected - I am assuming the temp sensor is the one on the water pump - not the tightest fit but definitely in. It's got 4 connectors in the clip....

Charlie

Not sure ANT, I'm a p38 man not a l322. Saint will tell you but I think he's away at the mo.

There are two temp sensors on the V8...the first one which is the most visible on the water pump, from what I can determine this is used to turn on and off the electrical cooling fan for additional heating.

The Second is mounted on the bottom radiator hose, this is called the radiator outlet temp sensor.

The Coolant gauge is driven from the one on the top of the pump, the ECU sends out a voltage on the Yellow/Green wire and then the ECU measures the return voltage on the Brown/Orange wire....

The sensor works on the Negative Temperature Coefficent which means as the temp increases the resistance decreases....so a short to earth on the Brown/Orange wire will cause instant temp reading in the read.

Pull up the hidden menu Test Number 7 on the message display and get the temp reading as a digital readout....

When my water pump went pearshaped I had the gauge in the red and the digital readout was -128!!!!

So...if yours instantly shot into the red then it is electrical...if it did it after a few minutes of running, it could be a massive airlock or stuck closed stat!

tomcat59alan said:

Not sure ANT, I'm a p38 man not a l322. Saint will tell you but I think he's away at the mo.

Click to expand...

hey tom you done deedpole recently

td5nut said:

bluddy`ell,wot drewyer to a brake light bulb mucker?

Click to expand...

nothing it was a fluke find, only after noticing the bulb out & changing it we actually realised it had fixed itself. spooky really but them were the days when you had to be a millionaire to own your own diagnostics.

wil2813 said:

hey tom you done deedpole recently

Click to expand...

Just before you 813.

Impressive...and thanks for the replies thus far

Saint.V8 said:

The Coolant gauge is driven from the one on the top of the pump, the ECU sends out a voltage on the Yellow/Green wire and then the ECU measures the return voltage on the Brown/Orange wire....

Click to expand...

I wonder why - 4 pins? I noted this youtube video that implied 2 pins were the in/out for the ECU and the other 2 pins were for the gauge, why they would be separate I don't know:

https://www.youtube.com/watch?v=eXNBlH0c4_U

Saint.V8 said:

The sensor works on the Negative Temperature Coefficent which means as the temp increases the resistance decreases....so a short to earth on the Brown/Orange wire will cause instant temp reading in the read.

Click to expand...

A standard thermistor I guess

Saint.V8 said:

Pull up the hidden menu Test Number 7 on the message display and get the temp reading as a digital readout....

Click to expand...

I'll look up how to do this

Saint.V8 said:

So...if yours instantly shot into the red then it is electrical...if it did it after a few minutes of running, it could be a massive airlock or stuck closed stat!

Click to expand...

It went straight up to red. Electrical it is.

As for fixing, I guess I just find the break using a multi-meter on ohms and trace back to that box containing all the wires that resembles the inside one of the green BT boxes in the street that look like an electricians worst nightmare!

Thanks for this - it was a sod to have this problem after a good 8 hours working on the car....

Charlie

Saint.V8 said:

The sensor works on the Negative Temperature Coefficent which means as the temp increases the resistance decreases....so a short to earth on the Brown/Orange wire will cause instant temp reading in the read.

Click to expand...

Saint,

I found the wiring diagram - thanks, image attached. Out of interest what do you think the black/red + purple / dark purple channel is for, one end is open?

Charlie

charliedurrant said:

Saint,

I found the wiring diagram - thanks, image attached. Out of interest what do you think the black/red + purple / dark purple channel is for, one end is open?

Charlie

Click to expand...

That is the for the Instrument Pack gauge....the purple isn't open circuit, it is the way they have drawn the IP box, it indicates that the whole IP and its inputs hasn't been drawn completely due to space so it only shows what is relevant to the system you are looking at. The convention is a box drawn with gaps just at this time the purple wire is shown entering at the point there is a gap!

If that makes sense!

Saint.V8 said:

That is the for the Instrument Pack gauge....the purple isn't open circuit, it is the way they have drawn the IP box, it indicates that the whole IP and its inputs hasn't been drawn completely...

Click to expand...

Thanks....it makes sense, however:

1) Why do you think there are two reference voltage lines?
2) One is earthed to the starter motor and one to the alternator. Does this explain why the temp during starting reads okay then when started goes to red?

Charlie