Planet 9

Owen Birch · #1 07-03-2009, 11:30 PM

I've noticed in 105 degree traffic, the coolant temp per the gauge remains the same (about 177 degrees).

I used to have a Mazdaspeed 6, along with a DashHawk (which would tap into about any parameter in the car's computer). In traffic, the coolant temp would get up to 225, displayed on the DashHawk, while the car's gauge remained in the same place.

Are our cars super-cool, or is the gauge like most other cars that only move when the temp is REALLY high? I ask because the guage has temperature number readings, not the "Low, Normal, High" seen in other cars.

**Craig@Rennstore.com** · #2 07-04-2009, 12:03 AM

VERY typical for mfgrs to control the temp readouts via gauge to remain steadily the same - despite the actual changes.

**Gator Bait** · #3 07-04-2009, 12:37 AM

Yes, our gauge will not reflect anything except an extreme temperature change. Mine never budges from the middle either once it gets there.

**blueone** · #4 07-04-2009, 12:48 AM

As the others have said, the gauge lies. Any number of OBDII-based data collectors will show you the actual temperatures. I've sampled mine a few times and saw temps in the 195-200F last summer in traffic, yet the gauge stays centered. BMW does the same thing. Consider it equivalent to an idiot light of sorts.

**STLPCA** · #5 07-04-2009, 06:06 AM

As has been discussed in many threads, the temp gauge is little more than an animated idiot light.

Gator Bite · #6 07-09-2009, 01:06 PM

A real shame. I want as much info as I can get. But I guess Porsche got tired of owners making service appointments because the water temp moved a little.

I wonder if there is anyone within the club that could work up a software flash for our instrument cluster that would make it more real time accurate. Anyone know anything about this?

***Greywolf*** · #7 07-09-2009, 10:28 PM

I'd be interested in that too. Be nice if the analog speedo could be reprogramed to read oil pressure at the same time.

Mike Foxtrot · #8 07-09-2009, 10:33 PM

Exactly where in the cooling circuit does the gauge pick off the temperature? Coolant coming right out of the engine before it gets to the radiators will be very high. Coolant coming right out of the radiators will reflect the cooling that has taken place on its journey through the radiators and be low. So is the gauge telling you that the cooling system is working by showing the low temperature, or is it telling you the hottest temperature at the engine? If it shows the low temperature and if the coolant system has a lot of overhead and is well regulated by a thermostat and fans, it may not be surprising that the gauge doesn't move much.

So which is it?

Mike Foxtrot

**blueone** · #9 07-09-2009, 10:53 PM

Originally Posted by Mike Foxtrot

Exactly where in the cooling circuit does the gauge pick off the temperature? Coolant coming right out of the engine before it gets to the radiators will be very high. Coolant coming right out of the radiators will reflect the cooling that has taken place on its journey through the radiators and be low. So is the gauge telling you that the cooling system is working by showing the low temperature, or is it telling you the hottest temperature at the engine? If it shows the low temperature and if the coolant system has a lot of overhead and is well regulated by a thermostat and fans, it may not be surprising that the gauge doesn't move much.

So which is it?

Mike Foxtrot

Coolant temperature sensors are always somewhere in the engine, normally in the coolant output path. I haven't found a diagram for exactly where they are in the Porsche engines. There are two, one for the engine control computer and one for the dash gauge. They must be very easy to access because the labor time for replacement is essentially zero, according to ALLDATA.

Owen Birch · #10 07-10-2009, 01:05 AM

My beef is that the gauge displays numbers not "Low Normal High". Because it displays numbers, it should be accurate, which it clearly isn't (sometimes by a lot).

Mike Foxtrot · #11 07-10-2009, 03:40 AM

Perhaps someone with a IR temp sensor gun can "shoot" the radiator while the engine is running and see how close it comes to the gauge.

Mike Foxtrot

ul2fly · #12 07-10-2009, 04:58 AM

I was thinking the same thing, sitting in 104 deg traffic the other day with a/c blasting. But I quickly remembered the time I had the car on the track in 100+ temps last summer without any issues at all, our cars have got a very good cooling system to put up with track use under high temps so I would not be too worried. Also the fan in the right side vent will regulate engine bay temps as well.

Stay thirsty my friends...

**blueone** · #13 07-10-2009, 10:47 AM

Originally Posted by Mike Foxtrot

Perhaps someone with a IR temp sensor gun can "shoot" the radiator while the engine is running and see how close it comes to the gauge.

Mike Foxtrot

What would be the use of that? Because you think there will be a correlation between the gauge and the actual coolant temperature at the radiator? For one thing, you'd have to remove the underbody cladding just to see the hoses to zap them with the IR thermometer. Why bother when you can just hook up an OBDII data collector, hardware or software, any one will do, and get the sensor input the engine management system uses? Then you can know the coolant temp +/- 1F. This is what several of us have done and posted the results. Also, incidentally, this is the data source used to regulate the continuously variable fan speed.

Mike Foxtrot · #14 07-11-2009, 12:40 AM

I think we are beating this thing to death. The original post questioned the accuracy of the gauge. I just thought that if you separatly determined the temperature of the coolant where the gauge picked it off and compared it to the gauge reading you would have the answer. I have tracked my car and even pulled my trailer over mountain roads at temperatures over 105 deg F and the gauge always pointed straight up. For all of its almost 50k miles, the coolant sight gauge in the trunk of my '06 S has not varried at all. So I guess the system works. I will, however, become worried if the temp gauge goes past vertical.

Mike Foxtrot

oscaput · #15 07-11-2009, 03:58 AM

As others have noted the water temperature gauge is not accurate or linear at all. I have observed the OBD readout to be as high as 210 degrees with a ScanGaugeII reader while the needle stays pegged at 175.

When I purchased my 07 used about a year ago it had a faulty temperature sensor which would work until the temperature (according to the OBD readout) was around 125 degrees or so. Typically I would get a warning of a faulty sensor at this point which would go away once the temp was over 175 degrees. It would occasionally generate a CEL code as well. This became particularly troublesome when I parked after driving and tried to resume driving after an hour or so. If the actual water temperature was between 125 and 175 and the OBD would read out a value of -40 degrees. If the engine didn't start right away it would flood out as I presume the electronics would set the fuel mixture for a winter morning start. Several times I was forced to let it set for a while until a accurate temperature value was being sent. The problem was solved by replacing the sensor although it was a bit of a pain as I live 60 miles from the dealer and it required two trips - one to confirm what I knew to be the problem and have the part ordered and a second trip to replace it with a need to have it stay overnight so the coolant was cold and they could drain it.

**Yancy** · #16 07-19-2009, 10:26 AM

I'm a historic bitcher about this one (drives me crazy that Porsche has an idiot light with a needle on the dash).

I have a Scan Gauge II installed which shows the actual coolant temperature (the one the DME uses...) and last weekend I hit a new record.

Actual coolant temp: 214 degrees F. Dash gauge reading: 175. (overheat is at 225...)

That should have put the needle more than half way to the red zone (from "normal" which is pointing straight up).

I would recommend getting something like the SGII (or other ODBII reader you can leave installed) if you care to know how hot your engine coolant actually is. Another interesting stat I have displayed along with coolant temp is the intake air temp. That can be a good indicator of your engine compartment temperature, which I find informative at times...

Gator Bite · #17 07-19-2009, 02:34 PM

You guys know I love Porsche, and routinely defend them on stuff. But this is a freaking joke man. No oil pressure, no oil temp, no voltage, no water temp. What do we have? Tach, Speed and Fuel. Is this a sports car or not?

**AJK** · #18 07-19-2009, 09:33 PM

Agreed!!!!

***alan93rsa*** · #19 07-20-2009, 08:44 PM

I just got back from a 3 day weekend at Putnam Park with my new 09 CS - PDK/PASM. Never once did the needle exceed 175. Even sitting in the pits with the fans cycling off and on after a hard 30 minute run.

Jim Michaels · #20 07-20-2009, 09:22 PM

I sense a new Porsche option: the Complete (and truthful) Gauge Option; $1,090.