[bus_ter]

Odd coolant temperature reading fault.

The last couple mornings the car has shown the coolant at 90C right from start. After 5 minutes of driving it suddenly starts reading normally (dropping to 30-40C and then building up to 90C over 10 minutes or so).

Anyone seen this before? It could go unnoticed if you don't pay attention to the gauge at the start of a journey.

I've always been suspicious of the gauge. Once warmed up it sticks at 90C religiously. Never deviating from this temperature regardless of outside temperature or how hard I'm driving. Makes me wonder if it's another ECU controlled 'fake' gauge rather than a genuine temperature sensor reading.

Oil temperature gauge does vary depending on conditions.

It's obviously an impossible value. But it also doesn't seem like a temperature sensor fault (why would it stick at exactly 90C then start reading correctly after 5 minutes). I'm leaning towards a software issue, but I'm only guessing.

 

[MR69 ALB]

This could be a number of faults and i would definitely get it checked out,
the fault is more than likely a duff sensor but the temp gauge does go down after 5 minutes of start up (sensors usually work or don‘t work consistently when they fail) this is a classic sign of air in the system which may be trapped in the thermostat housing right at the position the temp sender sensor is located On the highest point of the cylinder head, after five minutes of running the thermostat opens and fills the void with coolant Thus causing the sensor to read cooler.
depending where this possible air trapped is located This if not fixed could cause a hot spot within the cylinder head and cause warping and head gasket failure.

I don't want to be doom and gloom i am just pointing out other possibilities and have it checked out - no harm done either way prevention is better than cure.

Cheers Andrew

 

[GregW]

OP—that's not the way mine works at all. It starts off at ambient temperature and then rises. It usually stays close to 90°C but does vary in hot temps or sporty driving. As Andrew says, get it checked.

 

[bus_ter]

So I watched the coolant temperature carefully this morning. It doesn't start at 90C, but it gets there quickly. I'm sure it used to take 10 minutes or so from gentle driving. Instead it took about 2 minutes, then after a short while at 90C it goes back down to around 70C and then builds up normally back to 90C.

 

[MR69 ALB]

Hi Buster,
definitely sounds like low coolant or trapped air - Have it checked out mate or it could be very costly

 

[bus_ter]

Thanks for the help. I've emailed my dealer describing the issue as clearly as possible. I'll see what they say.

-------------
Hello Good Afternoon,

Please forward this on to the correct department.

I'm experiencing a change in behaviour of the coolant temperature gauge in my 2018 718 Cayman that may be indicative of a problem.

Normally I expect a gentle rise to operating temperature (90C) over 10 minutes or so from starting the car. However I'm now seeing the coolant temperature rapidly rise to 90C over a couple of minutes, and then start falling back down again to maybe 60-70C before then steadily building back up to operating temperature at the normal rate.

I don't believe this is correct behaviour and I'm concerned there maybe a coolant issue (air block etc?)
-------------

 

[bus_ter]

Well I haven't had a reply, yet.

However I think I may have 'solved' the issue. I nearly always start my car in Sport (I like the starting sound and how the car drives), however recently I've been leaving home early and so as not to wake the neighbors I've left it in normal.

Now it seems the car cools differently in different modes. In Normal it seems to try and warm the engine as fast as possible. In Sport it seems to be max cooling from engine start.

My theory is that in Normal mode the car maybe let's itself warm up before the thermostat is triggered and then starts the cooling. Thus seeing the quick rise in temperature, then drop, and build up.

In Sport mode the thermostat opens right away explaining the slow gradual build in coolant temperature (and general lower oil temperatures).

I've done a couple cold starts in both modes and so far has followed this pattern.

Can anyone confirm this??

 

[MR69 ALB]

Hi,
this does not ring true for any engines that i have been involved with, the engine cannot determine whether it decides to warm up quicker (unless there is a pre heat circuit which is sometimes Electrically assisted or on other engines a catalyst heated by fuel which is normally associated with vehicles operational in artic conditions)
sure there is a closed circuit that heats up quicker But that is so the heater works first to defrost windows and de mist, then the thermostat opens and the rest of the cooling circuit becomes one.
The engine warns up as quickly as you rev the engine There is direct influence over heat generated and How much pressure you press the gas pedal.

i think that your clutching at straws in trying to come up with an alternative explanation Of your fault, which clearly is a fault.
Rather than an email why dont you just swing by a local porsche dealer for their opinion on what is going on i would do this for sure as is my £70k that’s invested in the car.

Cheers

 

[Jack]

My experience is even if I start the car in SPORT or NORMAL, the water temp goes up quite quickly but it stays always at 90° degrees ... I never saw it less than 90° after reaching it...

There is something is not working correctly.

Different is for the oil temp (there is another 3D on that) in SPORT mode there is a mechanism of valves to increase the oil cooling

 

[bus_ter]

So eventually got an answer. This is normal and expected behaviour.

 

[718boxster]

sorry wrong thread

 

[987norway]

Hello,

Did any of you figure out what’s wrong?
My dad has this problem on his base 718.

Normal: water temp reach 90 relatively fast, then drops to 50-60, then builds up to 90. Maybe a couple of times before stabilizing at 90.
Sport: water temp may be a bit slower to reach 90, but does not drop.

The car was at the Porsche dealership a number of times last year due to this. Documenting, troubleshooting and waiting on replay from Porsche AG. They didn’t tell him why or what caused it to happen or even what they replaced, but they fixed it.

Now after a regular service at the dealership the fault is back. And the same process with documentation, troubleshooting and waiting on Porsche AG.

So any tips on what really is failing would be much appreciated. Could it be a failure in the changeover valve?

 

[bus_ter]

Hello,

Did any of you figure out what’s wrong?
My dad has this problem on his base 718.

Normal: water temp reach 90 relatively fast, then drops to 50-60, then builds up to 90. Maybe a couple of times before stabilizing at 90.
Sport: water temp may be a bit slower to reach 90, but does not drop.

The car was at the Porsche dealership a number of times last year due to this. Documenting, troubleshooting and waiting on replay from Porsche AG. They didn’t tell him why or what caused it to happen or even what they replaced, but they fixed it.

Now after a regular service at the dealership the fault is back. And the same process with documentation, troubleshooting and waiting on Porsche AG.

So any tips on what really is failing would be much appreciated. Could it be a failure in the changeover valve?

Hello,

Yes mine behaves exactly as you described. It never drops in Sport modes. But it does it in normal mode sometimes. It will reach 90C very quickly, then fall back slightly before returning to 90C and staying there for the rest of the journey. The car also needs to be completely cold for it to happen. If I've used the car a few hours earlier and the engine is still warm it never does it. You need to have a keen eye to spot it, and be watching the gauge for the first 5 minutes of driving away.

In the end I went to my local Porsche dealer and showed them a video I made demonstrating the issue. They told me it was completely normal and nothing to worry about. They also told me the coolant gauge was software manipulated. There's a range of temperatures (I can't remember the exact values but something like 75-115C) where the guage will always show 90C. If the temperature goes outside that normal operating range then it will start moving and show the real temperature. For example if the temperature raises to 116C (using my example range above) the temperature will start raising fairly quickly upwards from 90C. Likewise if the temperature goes above 75C at the start of a journey then drops below 75 for a few seconds and then goes back over 75, the gauge will show the temperature going to 90, falling back below 75 and finally going back to 90. But in reality the temperature has only changed a few degrees. I hope that makes sense?

It was about a year ago I noticed this behaviour. I've driven 10'000 miles+ since and I've stopped looking at the gauge. It's never once produced a coolant or engine warning message, and the engine has never missed a beat. I took their word that it was completely normal and forgot all about it.

At the time I remember thinking that if it was a hardware fault (like a dodgy sensor or valve), then why would it only do it in normal mode but not in sport mode? More likely the way the software controls the engine temperature and cooling was at play.

Now it's quite possible I've been living with a fault for a long time, and their information that it was normal was incorrect. If that's the case then I want to know about it!! So if Porsche turn round and 'fix it', please find out exactly what was happening so I can approach my dealer with some good information and evidence from Porsche.

 

[MR69 ALB]

Hello,

Yes mine behaves exactly as you described. It never drops in Sport modes. But it does it in normal mode sometimes. It will reach 90C very quickly, then fall back slightly before returning to 90C and staying there for the rest of the journey. The car also needs to be completely cold for it to happen. If I've used the car a few hours earlier and the engine is still warm it never does it. You need to have a keen eye to spot it, and be watching the gauge for the first 5 minutes of driving away.

In the end I went to my local Porsche dealer and showed them a video I made demonstrating the issue. They told me it was completely normal and nothing to worry about. They also told me the coolant gauge was software manipulated. There's a range of temperatures (I can't remember the exact values but something like 75-115C) where the guage will always show 90C. If the temperature goes outside that normal operating range then it will start moving and show the real temperature. For example if the temperature raises to 116C (using my example range above) the temperature will start raising fairly quickly upwards from 90C. Likewise if the temperature goes above 75C at the start of a journey then drops below 75 for a few seconds and then goes back over 75, the gauge will show the temperature going to 90, falling back below 75 and finally going back to 90. But in reality the temperature has only changed a few degrees. I hope that makes sense?

It was about a year ago I noticed this behaviour. I've driven 10'000 miles+ since and I've stopped looking at the gauge. It's never once produced a coolant or engine warning message, and the engine has never missed a beat. I took their word that it was completely normal and forgot all about it.

At the time I remember thinking that if it was a hardware fault (like a dodgy sensor or valve), then why would it only do it in normal mode but not in sport mode? More likely the way the software controls the engine temperature and cooling was at play.

Now it's quite possible I've been living with a fault for a long time, and their information that it was normal was incorrect. If that's the case then I want to know about it!! So if Porsche turn round and 'fix it', please find out exactly what was happening so I can approach my dealer with some good information and evidence from Porsche.

If you purchase a icarsoft por2 or equivalent you can actually monitor the true values of all sensors in real time, you will be surprised the amount of duff information that the display reads out, its more akin to (and the software is probably written by a descendant of) Goebbels propaganda peddled during WWII for the amount of incorrect make you feel good data it displays .

Cheers

 

[bus_ter]

You're not wrong. The heavy manipulation of the actual real temperatures doesn't help with diagnosing issues.

Ironically they've probably done this to stop owners worrying about the values shown..