Fluctuating temperature

[AldridgeZ3]

I have recently had a problem with my temperature skyrocketing with no apparent explanation. Before this it was driving fine for short and longer journeys for about a year without any issues. It is a 1997 Z3.

I will start by saying that I have bled the system, the heating seems fine and the car has a new radiator, thermostat, water pump, temperature sensor (and a few other hoses etc) since 2019. Oil level is fine, oil is clean and no traces of water.

I first noticed the issue when I entered the motorway and it temperature shot up when I got up to 70mph. As I eased of the gas it came back down immediately, but when accelerated again the dial went straight up to red again so I limped off the motorway and she was fine.

Since then I have had the same issue several times but driving round town at 20-40mph. The gauge starts flickering erratically. If I keep driving for a minute then the temperature eases back and settles again. At idle she has no problem. When the temperature rises it does not do so gradually, it shoots straight up into the red as high as it can go and will cool down almost as quickly.

Has anyone had this problem? My next step, when I find the time, is to flush the coolant system incase there is some debris causing a small blockage. I wanted to see if anyone had any advice first.

 

[Robert Hill]

Use a laser temp to check engine temp see photo

 

[NZ00Z3]

Yes, the rate of change seems to be too quick for an actual temperature spike in the engine. Sounds more like an electrical problem.

I agree with @Robert Hill , Use a laser temp to confirm your engine's temp.

You can also monitor the engine temp while driving with the instrument cluster hidden codes. See this thread: https://www.bimmerforums.com/forum/showthread.php?736153-Test-Mode-Hidden-Codes-in-your-car!

There are instructions in post #1 and #12. Read them both and see which one applies to your car.

• If the gauge peaks when the cluster code does not, then its a gauge problem.
• If the gauge and the cluster code peak at the same time, then its more of a sensor problem

 

[137699]

Sounds like you have an airlock in the coolant system. Try bleeding it - see if it goes away...
Though often airlocks are caused by leaks - water out / air in.

 

[AldridgeZ3]

Yes, the rate of change seems to be too quick for an actual temperature spike in the engine. Sounds more like an electrical problem.

I agree with @Robert Hill , Use a laser temp to confirm your engine's temp.

You can also monitor the engine temp while driving with the instrument cluster hidden codes. See this thread: https://www.bimmerforums.com/forum/showthread.php?736153-Test-Mode-Hidden-Codes-in-your-car!

There are instructions in post #1 and #12. Read them both and see which one applies to your car.

• If the gauge peaks when the cluster code does not, then its a gauge problem.
• If the gauge and the cluster code peak at the same time, then its more of a sensor problem

Thanks this is very useful!

I have the 15 test one so I found this: https://www.zroadster.net/forum/viewtopic.php?t=20201

For test 5 it reads n0 t1 which I don't think is good. Though I am not sure how old these readings are. I am not all that savvy with the computer stuff. I suppose I will see if I can reset it to get a recent reading. (There are a few other test results that don't make 100% sense to me too.)

Not sure what my next steps would be if this reading is correct. I have been think about getting a temp gun like Robert Hill says.

I didn go for a drive the other days without any issue but I will keep investigating.

 

[AldridgeZ3]

*UPDATE*
Car has been perfect since June. (I am not aware that I did anything to fix it). Yesterday it played up again, same thing. Temperature shoots up all the way when slowing/stopping but cools insanely quickly. I tried to jump out at the lights to get a reading with the laser temp checker but by the time I had my door open it had cooled (temp was all good FYI).

I bled the system and it did not fix it.

Any ideas?

 

[hard top]

I just did a quick search online and it came up with this, might be of some help ?

The rise in temperature is due to the fan clutch not engaging the fan clutch until the temperature gets too high.
This is the first indication that the cooling fan clutch is going bad. If you replace the cooling fan clutch using the correct one for your vehicle, it should fix the temperature problem.

 

[the Nefyn cat]

I tried to jump out at the lights to get a reading with the laser temp checker but by the time I had my door open it had cooled

Got the feeling that it's an electrical problem , maybe with the temperature sender, and not an actual engine temperature problem. Cooling down before you can get out of the car doesn't sound right at all.

 

[AldridgeZ3]

Got the feeling that it's an electrical problem , maybe with the temperature sender, and not an actual engine temperature problem. Cooling down before you can get out of the car doesn't sound right at all.

This has also occurred to me since the speed of the temperature change seems too quick for thermo dynamics to allow... but I am terrible with all things wire and electric so I don't know how to diagnose / fault find / fix. Do you know where I could start?

It has also occurred to me that there is something (air/debris??) in my coolant system that can reach much higher temperatures and triggers the fluctuation when it passes the sensor but this theory doesn't seem right for a number of reasons.

 

[Andyboy]

A faulty viscous fan would result in low speed overheating.

 

[137699]

You said you bled the system.... when exactly did you bleed it?
Was it in June? As the fact that you have had no issue since June suggests the bleed worked for a bit - but over time if you have a leak you're gradually getting more air into the system until you get an airlock issue happen again.

Bleed will alleviate the issue temporarily, won't fix the issue - you have to find the source of the leak - engine hot & running - car in the air on a ramp - get underneath and check all pipework very carefully for signs of weeping.

 

[AldridgeZ3]

You said you bled the system.... when exactly did you bleed it?
Was it in June? As the fact that you have had no issue since June suggests the bleed worked for a bit - but over time if you have a leak you're gradually getting more air into the system until you get an airlock issue happen again.

Bleed will alleviate the issue temporarily, won't fix the issue - you have to find the source of the leak - engine hot & running - car in the air on a ramp - get underneath and check all pipework very carefully for signs of weeping.

I bled it yesterday. First thing I did when I noticed the problem reoccurring. No improvement. I wouldn't be surprised if it did have a very small air leak but there is no obvious evidence of it. (also like you say, bleeding would be a temporary fix if that was the problem)

Also N.B. On shorter drives (but when the engine still reaches running temp) these symptoms do not appear. Only seems to do it if the engine has been running for a while that day or has done several journeys.

 

[Rudyrov]

Try a new temperature sensor, maybe even take the sensor out first and clean it and the cavity it fits into to make sure that there is junk or what have you. Make sure that you get coolant out of the hole before you put it back. I have no proof that there is, just something else to try.

 

[AldridgeZ3]

I just did a quick search online and it came up with this, might be of some help ?

The rise in temperature is due to the fan clutch not engaging the fan clutch until the temperature gets too high.
This is the first indication that the cooling fan clutch is going bad. If you replace the cooling fan clutch using the correct one for your vehicle, it should fix the temperature problem.

I understand that there are a couple of basic tests for this (https://www.bimmerforums.com/forum/showthread.php?1424369-Fan-clutch-test) If I spin by hand when cold it won't even freewheel for 1/2 a turn. When warm it will spin a few times.... While the engine is running (at running temperature) I can stop the fan. So in theory this means the fan clutch is okay??

Try a new temperature sensor, maybe even take the sensor out first and clean it and the cavity it fits into to make sure that there is junk or what have you. Make sure that you get coolant out of the hole before you put it back. I have no proof that there is, just something else to try.

The temperature sensor is reasonably new. Although, I agree this does not guarantee that it is not faulty, however the rest of the time it gives pretty accurate readings.


**UPDATE*
This arvo I managed to get the car to sustain the high temperature while I ran around with the temp laser gun to get a measurement. All temperature readings are what they usually were:
* 60°C-80°C in most areas of the block
* no more than 95°C in the very hottest areas on the block
* the radiator varies from about 45°C-75°C depending on where I measure it.
* two main coolant hoses in and out of block on the thermostat read about 40°C-50°C on one and 60°C-75°C on the other
I am not sure what the usual external laser temp readings of other Zeds are but this seems to be standard for mine?

I also managed to get a video of the erratic flickering of the temp gauge but I cannot upload it because it's a mp4 file.

Also cheers for all the comments, all suggestions are and have been appreciated!

 

[the Nefyn cat]

All the temperatures are round about what they should be, the hotter of the two pipes by the thermostat housing will be the one heading to the top of the radiator, there should be a lowering of the temp as it goes down the rad and then back to the engine to get heated up again. If the gauge is flickering that would tell me that there's a problem in the electrical side of things, gauges tend to be made to read a fairly steady temperature to stop people panicking when they see the temp going up and down as the thermostat opens and closes.