Weird temp gauge readings this AM

[5chn3ll]

My 996 has been parked for a week or two for...reasons. I need to get it smogged and the drive cycle still isn't done, so I drove it to work today in cold-for-me (approx. 50 degrees F) weather.

My office is only about 10 miles from my home. While cruising at about 70 on the freeway, I noticed that the temp gauge was reading abnormally high, pointing at the tick mark between 180 and 250. There was no other indication that anything was wrong; the low coolant indicator wasn't flashing, and nothing smelled unusual. I clicked on the AC to force the fans on; no change. I turned off the AC and turned the heater to full to use the heater core to cool things off; no change.

I pulled off at my normal exit and went to 7-11 as usual to buy some caffeine. The car was parked for no more than 3-4 minutes. When I fired it back up, the temp gauge was pointing straight up in its normal position, and it remained normal for the rest of my drive to work. There's no way it was parked long enough to cool off, and I don't think it makes sense that it would run cooler during surface-street driving than at 70 on the freeway on a cold morning.

I've never seen the temp gauge read that high before (I have the center radiator installed; it's always been nearly impossible to get the car too hot). I didn't mess with the HVAC controller to read the actual temps, but I will if I see this happen again.

Has anyone else ever noticed this behavior?

[32wildbilly]

My 996 has been parked for a week or two for...reasons. I need to get it smogged and the drive cycle still isn't done, so I drove it to work today in cold-for-me (approx. 50 degrees F) weather.

My office is only about 10 miles from my home. While cruising at about 70 on the freeway, I noticed that the temp gauge was reading abnormally high, pointing at the tick mark between 180 and 250. There was no other indication that anything was wrong; the low coolant indicator wasn't flashing, and nothing smelled unusual. I clicked on the AC to force the fans on; no change. I turned off the AC and turned the heater to full to use the heater core to cool things off; no change.

I pulled off at my normal exit and went to 7-11 as usual to buy some caffeine. The car was parked for no more than 3-4 minutes. When I fired it back up, the temp gauge was pointing straight up in its normal position, and it remained normal for the rest of my drive to work. There's no way it was parked long enough to cool off, and I don't think it makes sense that it would run cooler during surface-street driving than at 70 on the freeway on a cold morning.

I've never seen the temp gauge read that high before (I have the center radiator installed; it's always been nearly impossible to get the car too hot). I didn't mess with the HVAC controller to read the actual temps, but I will if I see this happen again.

Has anyone else ever noticed this behavior?

Never seen that behavior. How many times have you had the gauge cluster out to change the lighting? Maybe something got "compromised". Or perhaps the temperature sensor is getting wonky. I vote for #2 swag.

I call BS on "While cruising at about 70 on the freeway." unless of course this was a traffic jam situation.

[Dr_Strangelove]

You really need to find yourself in a situation where you're dead certain the car is not overheated but the gauge is displaying an incorrect reading...

It sounds almost like the behavior of a bad Oil Pressure Sending unit where the needle will display a higher-than-accurate number. But I have not come across many threads on the damn other place nor here about Coolant Temperature sensors going bad. Though - with this car I wouldn't be the least bit surprised it's capable of it.

I'll stay tuned for further troubleshooting.

[5chn3ll]

That's exactly what I was thinking when it was completely normal after restarting...

It sounds almost like the behavior of a bad Oil Pressure Sending unit where the needle will display a higher-than-accurate number. But I have not come across many threads on the damn other place nor here about Coolant Temperature sensors going bad. Though - with this car I wouldn't be the least bit surprised it's capable of it.

[5chn3ll]

I've had that stupid cluster apart countless times - but not in the past year or two.

And there was traffic, so unfortunately 70MPH was about right.

Never seen that behavior. How many times have you had the gauge cluster out to change the lighting? Maybe something got "compromised". Or perhaps the temperature sensor is getting wonky. I vote for #2 swag.

I call BS on "While cruising at about 70 on the freeway." unless of course this was a traffic jam situation.

I'm not going to sweat it until I see it happen again.

[gnat]

It's been too long, but our's did that once. I could be misremembering, but I think it was found that the thermostat valve was sticking. I just remember that it did it, I took it to my Indy, it didn't cost a fortune for a change, and it hasn't happened since.

[5chn3ll]

I wondered about that too, since it has been sitting for a bit...but I assumed the temps would continue to climb if the tstat was stuck closed. I'll keep an eye on it.

It's been too long, but our's did that once. I could be misremembering, but I think it was found that the thermostat valve was sticking. I just remember that it did it, I took it to my Indy, it didn't cost a fortune for a change, and it hasn't happened since.

[gnat]

I wondered about that too, since it has been sitting for a bit...but I assumed the temps would continue to climb if the tstat was stuck closed. I'll keep an eye on it.

It's been too long, but our's did that once. I could be misremembering, but I think it was found that the thermostat valve was sticking. I just remember that it did it, I took it to my Indy, it didn't cost a fortune for a change, and it hasn't happened since.

I want to say that Jake once said that if it was stuck closed you'd never know as the temp is taken on the cold side rather than the engine side. Again I could be completely misremembering though.

IF I am remembering our issue correctly, I don't think it was completely stuck. Just not opening completely so the coolant wasn't circulating as well as it should. This led to coolant staying in the motor longer and getting hotter.

[FRUNKenstein]

So, a weird electrical gremlin on a 20+ year old 996.

Clearly mice.

(I misspelled "ignition switch" above)

[5chn3ll]

Heh.

I performed a full Italian tune-up on the way home from the office, and no shenanigans were noticed.