Please help! Weird overheating
 

Hello all,

I read through many thread here but not one really relate to my exact problem. My car is a 1998 XJR, and I get a slight overheating in this hot summer heat. The temperature gauge would slowly go up past the middle if I have my car in park and sitting with the A/C on. The moment I start to drive off and shut off the air, the gauge drops back to normal.

Since a few weeks ago, I've been noticing very small puddles under the car direct underneath the front below the pullys. However, I cannot pinpoint exact where it's coming from. I've had to top off a few times, although it hasn't really been to the low warning point except once. I believe I may have just been topping it off out of paranoya because of the one time it came up with a red low coolant warning light because everytime I topped off, the coolant level is around or a little above the middle in the reservoir. Therefore, I may be overfilling that reservoir.

But with my overheating problem when I have my a/c on when parked or stopping for around 5 minutes and the temperature dropping back to normal once driving off and shutting off the air. Does anyone have any idea what that may be? Plus, the small leak; has anyone experienced this before and may be able to help pinpoint where it's leaking from. Thanks much in advance!

When it is idlling and the A/C is on, and it is overheating, are the fans running?

Do you have an OBD reader that will show you what the temperature is? The dash unit is inaccurate beyond mid-range.

For the leak: can you smell coolant? Look to the water pump, all hoses, including the short cross over pipe, check the thermostat housing area. My best guess: water pump is failing causing leak, overheating, and loss of coolant.

Run a search against all of the key words, above and you will learn a lot and where to examine your car.

If you search the archives you'll see a lot of people saying not to trust the temperature gauge. I agree with Jim above, get an OBD reader so you know what the real temperature is. I have an Ultragauge, and I keep it hooked up and sitting in the ashtray most of the time. Of course I also have the Realgauge mod too, but anyway, don't trust the temp gauge ! Make sure the coolant lines running to the reservoir are crossed - many posts on this. Also, the crossover pipe in the front sometimes gets old (plastic) and starts to drip, and there are heater hoses under the supercharger that can get old and leak. Then there is the coolant coagulation problem when orange and green coolant are mixed. Just don't let your engine get toasted !

I do not have a reader that can read temperature. While it is overheating with the A/C on, both fans are running. As for the leak, I can smell coolant.

I will recheck everything mentioned and do more research with those key words again. By the way; What is coolant coagulation and the effects/symptoms of it? I can't remember if the fluid was green or orange when I added the orange fluid to it.

Thanks very much for your help guys!