Variations in temp guage readings?

When I read my owners manual I find no clear definition of what is normal temperatures at normal running. The book goes from zero is for an engine not running, and then goes to red light just to the right of the 250 degrees point. It also states that the red light will come on at that point. For me that's more than hot enough to flash red lights. Another vague reference is that the needle should be pointing straight up. Using the guage and needle as it exists...in 80 degree weather and driving in city traffic my needle is just to the right of the 8 (in 180) and touching the 0. In heavy stop and go traffic, freeway or street, the needle moves to middle of the 0 and stays there. In air temps below 75 to 80, the temp sits to the right side of the 8 and off the 0. When the engine is running hot (in the mid 0) and I turn it off and then turn the ignition on but not starting the engine, the fans come on but it doesn't feel like that much air is being pushed through front of the vent holes. Is there another exit where the hot air is vented? In comparison, my GTI sits and 180 all the time and never moves except to go to 0 when not running. Coolant is clear and fine and up to level. Oil is fine and one notch below full. Curious what others are experiencing in 3.4 engines in mild to hot weather.

My 03 c4 reads 185 all the time. Hot or cold out, Slow or fast riding. Warms up quickly too. Couple miles and it's right there. Hope that helps.

Generally the 04 C2 sits right here after the initial warm up idle. Cold or Warm Weather, sea level or + 10,000'.

Seriously?

On the hottest days of summer mine will point straight through the zero. Normal out for a drive temp is straight through the 8. R

Quotes source post: 13011980

The temp gage is a crude indicator of actual engine temperature. It is little better than a warning light but it does at least show one the engine temperature is at some elevated level and one can then know after a while longer the engine is fully warmed up. If you want to know what the coolant temperature is your car may have the ability to display the coolant temperature via the A/C display. There is an A/C button sequence to activate this and to then select the coolant temp for display. I think all 3.4l models support this, but don't quote me. The AC Climatronic unit is actually manufactured by Audi. There is some sort of serial data stream (not CAN) that allows the AC unit to display engine parameters. This works on 1997-2000 boxsters. To switch from F to C: Hold down the recirculating button then push both the temperature + - buttons. To access diagnostics: Hold down the Recirculating & Air up buttons for 5 seconds. The + - buttons go up and down through the list of "c" codes. The center vent button switches the left display between the "c" code and its actual value. Press the Auto button to exit. Here is a list of what can be seen: 0c - ERL 1c - Oil Temp? 2c - Inside temp. Sensor mounted in the aspirator assembly at the side of the dash. 3c - Outside temp. Sensor located inside the air inlet of the A/C unit. 4c - Outside temp. Sensor located in front grill of the radiator. The data is fed to the Climatronic from the instrument cluster. When not moving, the instrument cluster OBC temp display retains it's last setting until moving. This is to prevent heat emanating from the radiator affecting the temperature sensor. The A/C unit uses the lower of the two outside air temp values in determining fresh-air temp. 5c - Outside temp. (matches with OBC outside temp display) 6c - Coolant temp. 7c - Footwell discharge temp. 8c - Sun sensor (dash top) 9c - Sun sensor. 10c - Passenger compartment fan speed. 11c - Passenger compartment fan voltage. 12c - Temperature mix Flap command 1=COLD, 100=HOT 13c - Temperature mix Flap position 14c - Central Flap command 15c - Central Flap position 16c - Footwell/Defrost Flap command 17c - Footwell/Defrost Flap position 18c - Recirculation Valve command 1=OFF, 100=RECIRC 19c - Recirculation Valve position (feedback) 20c - Vehicle speed in kph, updating only once per second. (real speed, not speed+safety margin as in the speedometer) 21c - Engine RPM in hundreds. This too only updates once per second. 22c - ? 23c - ? 24c - Sun sensor, exterior lights switch & panel lights control (term. 58 & 58d voltage) - used for A/C panel display illum. 25c - ? 26c - ? 27c - ? 28c - Fan speed? 29c - ? 30c - Engine run time in seconds (255 max.)(=0xff) 31c - Timing counter 32c - Displays test 33c - Software version? Mine states 3.4 34c - ? 35c - Outside temp. from inlet sensor (filtered?) 36c - temp? The claim is this works for "Boxsters" which is true but I believe it also works for early 996's. Or you can buy an OBD2 code reader/data viewer/data logger and view the engine coolant temperature in real time. What you will likely find, as I have when I've done this, is the coolant temperature varies quite a bit. It can be "low", around 185F on a cold day at a steady highway cruising speed. Or it can be "high", in my Boxster's case up to 226F on a real hot day around town, on the highway even. Depends upon how high the ambient temperature is.

Quotes source post: 13012427

Many many thanks. John

Quotes source post: 13011980

My, my1999 3.4 runs virtually identical to yours. The left edge of the 0 equates to between 190 - 200 degrees F (I think) which seems to be "normal" for this engine. I'm seriously considering putting the third radiator in during this "offseason" as I'm going to be doing some suspension work as well, so the car will be up on jack-stands.

More 996 paranoia. I watched the temp like a hawk with the temp hack. Would go between 93 and 104 Celsius depending on temp and driving conditions. That was between the 9 and 0 and past the 0. So to summarize...what you are seeing is normal. Ignore it.

^I don't think it's necessarily "paranoia"^... More like healthy respect for an overheat situation that could leave you with a repair bill in the $10 - $20,000.00 range. Personally, I haven't done the "temp hack", but I do keep an eye on my temp gauge for signs of unwarranted movement... :-)

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Me too. But I'm not sure what good it does. I can tell you based on my expeirence even with a radiator fan non-functional neither my Boxster or my Turbo manifested any indication at the temp gage there was a "problem". The only times I've had the gage needle climb to regions the needle has never been before was after hitting road debris with the Boxster and busting a radiator. The cloud of coolant vapor behind the car gave me a clue to what was to come even before the temp gage needle reacted. Same with the Turbo after hitting a mule deer. Long before the needle reacted I knew I was going to have to park the car on the shoulder and call for a tow. Even the loss of a serpentine belt might not have the needle budging much at least at first. If the water pump stops spinning no coolant flows past the temp sensor and thus the temp sensor won't register the severe build up of heat in the coolant in the heads. One is likely to spot vapor from a head gasket or head failure before the gage needle reacts.

I always go through a "new to me" car worry period. Finally got to do a good drive today, a run with about 40 or so PCA members through the Santa Monica mountains. Car ran nice a cool, the needle was right in the middle of the gauge...and the driving was aggressive. Later, going home in bumper to bumper Saturday afternoon traffic...mid to high 80s air temp, the needle climbed to the middle of the 0 and stayed there. Some track time and wet skip pad time at an Alfa Club driving school will complete my settling me in with the car.

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FWIW, I added the third radiator last year. It makes a difference at highway speeds ... otherwise, not so much. That's reasonable, I guess, given that there's no fan behind it.

A a strictly scientific experiment, I drove through the desert at 90 to 100, over 110 degrees F. Temp stayed pegged at this spot.

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Shortly after I bought my car out in Illinois and drove it home to Long Island, I was poking around under the engine lid and noticed that the coolant was a little below the "min" mark when cold. So, the following day as I was driving past the local Porsche dealership I dropped $50 for a gallon of "the Pink stuff"... After topping off the coolant (Between the min/max mark) I inadvertently screwed the cap on crooked... Suffice it to say, that the next time I drove the car a sufficient distance to get it up to full operating temp I wound up losing quite a bit of coolant. In addition, that light came on and the temp gauge did rise quite a bit - so I know it works...Good thing I bought that Gallon of coolant

Cuda: So the speed limit is elevated in the desert compared to "normal" areas?

Might be time to replace the coolant cap. I have had to replace the cap on both of my cars. A newer cap has a part # that ends is "02" or "04". (Might add I have had to replace the Boxster's oil filler tube cap twice now. Both times it was leaking at idle. The cap seal gets worn/old and the cap doesn't seal 100%. Figure replacing the cap every 100K to 150K miles...) Unless there is sign of coolant leaking out -- there is anti-freeze residue -- if it is just the cap leaking -- which is "common" -- all that is being lost is water vapor. So to top off the level all that is needed is distilled water.

+1 What Macster said. In addition when installing the new cap make sure you get it tight. Last year I swapped to the new "04" cap, thought it was tight...it as not. Water went everywhere! Reinstalled the old cap(tightly) but continued to smell coolant after pulling into garage with very slow coolant level loss. Went back to new cap, installing tightly. Problems solved! When you think it is tight, give it one more try and don't cross thread.

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No, the cap was fine (new part # - replaced by p.o)... Total user error on my part. Fortunately I was being "paranoid" and glancing at my gauges once in a while (I thought that's what they're there for...) and there was no lasting damage done! 😎