Engine Overheating

Does the coolant fan come on? Does the vehicle lack power when driving. It does have a rev limiter. Did you remove the rad cap and check level there?

I would start by replacing the thermostat first. Thats the logical problem and cheapest to do. Let me know how you make out after the thermostat

Which engine? And have any tests been done to see what is wrong?

What's the question and symptoms?

You haven't mentioned anything. How much water did you have to add? How long could it have been low? Do you see white smoke from the tail pipe? Does the radiator fan turn on intermittently? Does it only overheat when stopped in traffic or does it happen at highway speeds too? Is it not overheating at all now that you added water? What happens to the temperature of the air from the heater when the engine runs hot? Does the air burn your hand or is it rather cool? Do you see any puddles underneath the front of the car where you park it?

These are the kinds of things a mechanic would check to make a diagnosis. Since we're on a computer, you're going to have to provide all those details and observations.

Not referring to the air conditioning. If it overheats again, feel the air temperature from the heater. If it is really hot, at least we know it's circulating which means the coolant is going to the radiator. If the temperature is not hot enough, lack of circulation is the problem and that can be due to low coolant level.

You should not fill the reservoir to the top, just to the "max" line on the side. Most certainly there was some air in the cooling system so some of what you added went in there when you stopped the engine and it cooled down. It sounds like the cooling system and fan are working properly, and loss of coolant was the cause of the overheating. Fan problems will cause overheating only at slow speeds. A radiator plugged on the outside with a butterfly collection will cause overheating at higher speeds.

The thing to do now is keep an eye on the coolant level in the reservoir. It will go up shortly after stopping the engine because the heat is still going into the coolant and causing it to expand. After about a half hour the level will drop quite a bit but it should stay above the "min" mark.

If the level drops a noticeable amount in a few weeks or less, dye can be added to see where it's going. After driving a few days, you search with a black light including at the tail pipe. The dye will show up as a bright yellow stain. If it takes a month or more for the level to drop a quart, what leaks out could be evaporating fast enough to not leave a puddle. The dye will show that up too.

Also check at the 4" long rubber hose hanging down on the passenger side of the firewall under the hood. You might have to crawl underneath to see it. The open end will be formed into a thin slot. If you see dye there, the heater core is leaking. Typically that will get worse real fast and won't leave you guessing. Dye at the tail pipe means a head gasket is leaking. When that gets bad enough, you'll see white smoke from the exhaust.

Sounds like hose. May have been caused by thermostat but not likely.

Either case should not be too expensive. But you dont say what expensive to you is?

There could be several problems, like a faulty water pump, something simple like a bad radiator cap. Or a plugged heater core, you should have it pressure checked, then they can determine where your problem is, most people would automatically assume a bad head gasket, but that usually is accompanied by bad performance and even white smoke coming from the exhaust