Okay, this may take a minute to explain. Yesterday I'm drive the 30th in Austin when my A/C starts cycling cold and warm. I look at the temp gauge and it was steadily rising as I'm looking at it. I pulled into a gas station immediately and turned off the engine. I opened the hood and the engine did not appear to be extremely hot, no steam, coolant leakes, or smells. I did notice the fans would not come on with the ignition on. One fan came on when I turned the A/C on full blast. So I sat for about 1.5 hours and then put a bag of ice on the intake. When I check the temp again, according to the gauge, it was at 210. I t would not go much below that. I started the car and it started fine. I drove it a mile to Autozone, without A/C, to buy a multimeter. I checked all fan relays, fuses and temp sensor input voltage. All were good. I started to drive home, approximately 1.5 hour away and again without A/C. I continued to monitor the gauges. The low coolant light came on so I pulled over again. The coolant was fine. I noticed when the voltage would drop slightly, the temp went up and the oil pressure went down a little. However, as long as I was moving, the temp stayed constant (210), as it should as you don;t really need fans if the car is moving. I get home and start checking things again. The fans work, relays are good, temp sending unit is good and coolant is good. I read the owners manual and it says if the low coolant light is on and the temp gauge indicates hot then the engine will go into limp mode and can be driven up to 50 miles this way. The engine never ran bad or lost power. Nothing did as you might expect from an overheating engine. I checked the alternator and battery, all fine. Any ideas? I'm at a loss as to why this may have occured. Thank you for reading this.

 

The temp guages are not that accurate so as long as it sticks at 210 youare good . My car when it warms up to driving temp according to its guage is 210 all day and I got my fans kicking on early and a manual fan switch just from a long time ago .

That being said the only time my car went over 210 was when I did a cam swap and swapped the two small hoses underneathe the radiator cap (steam line , and overflow lines) . Lucky me I was just testing and was keeping an eye on the guages . So I did some reading about it and it turns out you can switch these two around and can ride for hours but as soon as you turn on the ac it will heat up .
Not too sure howthismay apply to your story but this is my experience and that of another that was read during my time of wondering about overheating .

 

The stock guage is a POS, I knew it was a dummy guage but its worse than most people think. I had my car on the dyno and the tuner said hey your cars getting warm and I'm going to shut it off to let it cool down. The car was at 228 degree's and the stock guage was reading just below 210 apearently it takes somewhere around 240-250 before the guage shows anything above 210. Found out only one of my fans is working. So now I need to figure out whats exactly wrong. If your guage is climbing higer than 210 it is really really getting hot, so beware.

-William

 

Thanks guys. I bought a new thermostat today and will get a sending unit tomorrow. The last time it "tried" to overheat and I replaced a fan relay. All was fine after that. This is really puzzling. The car never acted like it was overheated. The owners manual says it's overheated if the low coolant light is on AND the temp gauge is reading hot. Then the computer cuts out cylinders to reduce the heat and thus power. The manual clains to allow the car to be driven up to 50 miles like this. I don't see how. If it's hot, it's hot, pull over immediately. Anyway, still diagnosing with no results as to what may have caused this. Thanks for you input and time. Fly low.......

 

The car is fixed as far as I can tell. I changed the coolant, replaced the thermostat, added water wetter and changed the oil. I started it up and once I verified the coolant level I monitored the temp. It started to overheat in the garage. At the third line on the gauge (approximately 240 degrees) I heard the left fan come on. So I turned off the engine and replaced the relay to the right fan (relay number 1) and the fan came on while the engine was off. I then started the engine again an monitored the temp. It stayed just below the 210 mark, even with the A/C on max. I then drove her down the road and verified the temp. It is just fine now.

I understand what everyone is saying about the gauge being inaccurate and only being a "dummy" gauge. However, while watching it today I could see it fluctuate in small increments. It may not be accurate but, it appears to attempt to register an approximate temp. This may not be so. This is just my opinion.