Hey everyone, so I've been here before on an old account and you were all very helpful, hoping to get some help again.. I drive an 03 g35 coupe.. My car at idle doesn't really overheat, a few fluctuations while idle but always goes down on its own, while I'm driving slow or just stepson acceleration, the gauge will rise and the more speed I pick up the temp gauge goes down.. When the gauge is close to red, there is no burning smell or smoke from engine when I pop hood, it doesn't seem like it's overheating but I have no idea... Any suggestions? Or ideas why?

I'd start with thermostat and/or water pump. At idle your engine isn't doing much but as you're moving engine start to heat up. As you're moving if the thermostat is bad it will not flow coolant like its supposed to...when you go really fast and notice the temp go down is maybe from more air rushing through radiator and faster revving engine is forcing coolant to flow more at higher speeds.

Ok, what is the easiest way to check the thermostat? And I just noticed when it slowly starts to overheat, if I Rev engine and let off.. It normally cools down, which is what you said.. But wouldn't that mean it's not the water pump and more a thermostat issue?!

Yes Thermostat would be the first thing I check. As you rev the engine it can still move a good amount of coolant even if the water pump is bad or going bad.

Cooling temp sensor/sending unit

So if it was the cooling temp sensor, would that mean my car is not actually overheating.. Just the sensor is causing the gauge to spike?

Correct. It's just giving a false reading. It could be something else, so I'd change the sensor asap (or may be able to test it with a voltometer) to be sure. It's only like $30 tho so I'd just get a new one to be sure. It is most likely the sensor.

Easiest way is to put it in a pot of water, put it on the stove and see if it opens when the water gets to the proper temp.

Thanks for this!

Thanks for replies guys... So the thermostat is good... Checked it... How do I check the water pump?? Aside from coolant or water on ground, I heard something about ac system... It's ice cold.. But doesn't warm up even when set to 90°...

I'm having the same problem as well and definitely would like to know what is wrong.

A simple way to check that the water pump is in fact pumping water is to take the radiator cap off (only when the car is cooled off). Start the car and wait for it to warm up. Once it has reached temp you should start to see water flowing by the cap opening. If not there are one of two possibilities.

1. The water pump has completely failed. From what I've seen of the construction of the VQ's pump, that doesn't look probable. From the pictures it looks like all metal construction.

2. The thermostat is not opening. I know you said you checked it, but this is the most probable, easier and cheaper of the two options to fix. Put a new thermostat in before you start tearing out the WP.

Ok so I'll replace thermostat anyways and see if that helps.. But if the thermostat was bad and wouldn't open... Wouldn't that mean that it would overheat at any point, whether I'm idle or moving???

Correct. You'd seize the motor in a matter of minutes. You can run it with no thermostat if you wanna see if that that has any effect.

Dude you might want to replace the temp Sw. And thermostat. I had that issue with my S13 and the temp sensor/sender was the culprit.