Liquid Temp Sensor

So here is what I'm planning to do. I am wanting to build a monitoring system for a car's cooling system. I want to put a liquid temp sensor in the out flow of the radiator to see what the temp of the coolant is going into the engine and then display that info on a small lcd screen in the cab.

My question is what sensor would be best to use to actually submerge into the coolant and seal up. It would obviously be under the pressure of the cooling system so it would need to stand up to high pressure and high temps (above boiling temp of water). I've had the idea of using a copper wire and have it submerged into the coolant and then coming out and using some temp sensor to get the temp of the copper wire. And I'd obviously have to water proof and heat proof the sensor since it will be in the engine bay and subject to high temps (especially on hot days) and water proof for when it comes in contact with any form of precipitation.

you can measure the temperature on the outside, using thermal glue, like the one used to glue a cooler on a CPU.
And do some isolation on top.

Most metals are good heat conductors so the temp measured outside will be almost equal to temperature inside.
There is a small delay as the metal has to heat up/cool down

So unless you want every fluctuation in real time measuring on the outside is as good as on the inside. And will give you less trouble with sealing the thing, waterproof etc.