I would buy a Honda Civic. You can get new ones for around 20k. Im not sure how much they are, they are great on Gas too and very very very reliable. I would go Honda anyday over anything personally

If you want a faster car you will have to get one with a 6 cylinder engine. Some 4 cylinder engines are faster than others but in general 4 cylinder engines aren't fast. You can tell when a car has a 4 cylinder engine as it makes more noise starting up and when you drive. I can tell a car has a 4 cylinder engine when I hear it start. Like you said in general Toyota and Honda's are reliable. The Chevrolet Impala is reliable too but avoid model years 2000-2002 as they are known for numerous problems but from 2003-2005 they are more reliable. If you want a fast Impala avoid the base model with the 3400 or 3.4L 4 speed v6 automatic that has only 180hp, its a very slow engine and underpowered for this car. I know because I had a 2004 Impala with that engine. In the Impala get the LS or police model with the 3800 or 3.8L Series II 4 speed V6 automatic. Its much faster with 200hp and the engine is more reliable. I had one of those in a 1996 Pontiac Bonneville and the car was fast. For 2004-2005 there was an SS Impala with a 3800 or 3.8L Series II supercharged V6 with about 230hp. On the downside the 3800 Series II v6 4 speed automatic is well known for head gasket issues and is a common complaint with GM vehicles with that engine.

Preform tests using these tools before you do anything. Cooling system pressure tester kit Compression tester kit They are on free Loan-a-tool at Autozone. You pay full price for them and then when you're done you return them for a full refund. You want to rule out any major problems before proceeding to lesser problems. To answer your question; no there's a separate sensor for your gauge usually listed as a "Temp Switch".

At the risk of hurting your feelings, I would suggest you just upgrade to a newer vehicle that would naturally have more power than you 03 Pontiac. If you do all you have planned you are going to be spending somewhere in the area of $3,500 to $5,000 on this eight year old vehicle. Once you put that much additional power to all the other mechanical devices of your drive train you are setting yourself up for some other major expenses.