How does the clutch effect other components of the car

My car had started to overheat while at a stop light. My letting out the clutch I noticed the temp started to decrease? Was this a coincidence or would that actually help?

Also I have also wondered if letting out the clutch when going down hill or at any time I am coasting would that effect gas milage?

No connection between overheating, and clutch pedal depressed, or not depressed at stop light.

When you say “letting out the clutch” I conclude you mean depressing the clutch pedal

Don’t coast with the clutch pedal depressed, don’t roll downhill in neutral.

The declining temp was almost certainly related to you starting to move - thus pushing air past your radiator.

Chances are that your cooling fan and/or some part of that system (maybe a fuse or relay) have gone. If you watch you’ll likely notice the temp rise whenever you sit still and fall whenever you start moving. You should have someone check that out before you overheat the car and damage something.

Ditto. Perfactly described.

He didn’t say he started to move, just said he let the clutch out (sitting at a light in neutral was my conclusion)

Several miles of continuous driving (not stop-and go) would be required for the effect of moving air would be noticed. I know we can debate how far,and long you have to drive to bring the temp down on a car thats overheating due to non-operating electric fans (he didn’t even say the car had a electric fan) but in my experience the effect is not immediate.

Surely we will have to wait to see if the OP returns to tell us whether s/he noticed this after moving or while still sitting. You could be right that it was sitting still, but you have to admit that air movement makes more sense than the clutch. (I’ve always seen more or less immediate drops in temp with fan problems, but I’ve also always driven tiny little econoboxes).

I’ll bet that as you were letting out the clutch, you were also pressing on the accelerator as you would naturally do when starting out from a stoplight. When the engine speeds up, the water pump moves more coolant through the block.

I would want to know how old your radiator is rather than anything about a clutch. The fan motor may not work (FWD).

Why should you not go down hills in neutral?

Define what overheating means to you in this case. It may not be overheating at all and may just be getting a little warmer. Sometimes watching those gauges too close is the problem.

The mileage change with or without clutch going down hill depends.  Different cars act in different ways and different hills and speeds also make a difference.  

Some modern cars cut the fuel totally off when the accelerator is not depressed and the car is moving fast enough to be turning the engine above idle speed. In this case you save fuel by leaving the clutch out.  

On other cars this is not true and fuel will always be feed to the engine. This complicates things as some times depending on the grade and length of the hill and your car and what gear you are in.

That said the difference is generally very very small and not worth the work. In addition it is generally safer to leave the car in gear, especially if it is an automatic.

Because you don’t have as much control of the car. Especially if there’s a problem. In MOST states it’s illegal.

Thanks for all the answers and posts. To clarify when I came to a stop light and the car was stopped I did put the car in neutral and released the clutch. I noticed the temp starting to drop. When I pressed the clutch in and put the car back in gear the temp started to rise but that was also at the same time the light changed and then the air movement helped to lower the temp. Again thanks for all the help.

I wonder if you have an electrical problem relating to a ground. The negative cable of the battery is attached to the engine block. On many cars, there is a strap from the engine to the body. The engine sits on rubber mounts electrically isolating it from the chassis and body. If the ground between the block and the chassis isn’t good, then the ground may be going through the clutch. Assuming you have an electrical gauge for coolant temperature, a weak ground could vary the voltage the gauge receives when the clutch is depressed and then released. The engine probably isn’t changing temperature, but the gauge reading is changing.

At any rate, check the ground between the engine block and the body of the car.