Hi, I use a Nissan Altima 2002. Sometime ago the car overheated badly and I had to change the top cylinder with gasket including radiator from single cell to double cell. It worked. But another problem occured; the rpm became higher than normal making the car to rev up and down when at park or neutral. The engine sounds is also higher than normal. What do you think I should do?

Also.........

Best Practices

• To prevent an expensive, recurring problem, the integrity of the entire cooling system should be inspected and tested when a head gasket is replaced.
• During this repair, the cylinder head(s) will need to be inspected and machined. Additional repairs may be needed after the inspection, which can add several hundred dollars to the repair and are not included in the RepairPal estimate.
• Cylinder head gasket replacement often occurs when the engine has high mileage; several additional parts may be needed during the repair. These may include cooling system components (hoses, water pump, radiator, thermostat, etc.) vacuum lines, timing belt, ignition wires, and more. These will be in addition to the RepairPal estimate above.

Sounds like your thermostat may be stuck closed. When the car is at operating temperature, does warm air come out of the vents inside? If it's blowing cold air, then change your thermostat.

you are looking at a head gasket

Were the parts installed correctly? All wiring harnesses plugged back in? Did the Nissan quit running before parts were replaced? The overheating may have blown a head gasket.

If your car runs well, then the head gasket must have been the problem for the no start condition. The head could have warped causing a leak which caused the overheat condition, which lead to a further damaged head gasket.

4 cyl. cars are known for this problem, but it happens to V-8's as well.

Watch those coolant levels in 4 cylinder cars, especially.

A car when overheats means two things: (1) Timing may be off including electrical (2) bad head gasket. Chec for code reading with a OBDII reader to be more .
May need a tune up!

Which engine ? Put a drain pan under top radiator hose. There should be a cast part attached. Remove, you will see thermostat, pull install new, clean old gasket off, install new gasket with ORANGE HIGH TEMP PERMATEX SILICONE, re-assemble

what colour smoke? if white, you may have a blown head gasket, remove the radiator cap look for signs of oil in coolant, if low top up with water and start engine,if coolant is trown from radiator this confirms same, also look for external coolant and oil leakk on cylinder head.you can also check cylinders by re moving spark plugs cank engine and see if coolant srays out holes

Replace your radiator.

You might be lucky and only need a new radiator cap. The seal may have gone bad. If not there may be a small crack in the plastic of the radiator. It also sounds like you may need a new valve cover gasket. It's hard to tell without seeing what you have going on. :) Hopefully this helps get you going in the right direction.