'02 Nissan Sentra overheating question

120k miles. Loses coolent, but no apparent leaks. Oil is not milky. No extra exhaust as far as I can tell-live in Colorado, pretty cold.

Heater- barely works now. Dash temp gage also can go up while stopped at a light. Ideas? How do you know if (a) head gasket is bad, (b) water pump is bad, © thermostat is bad?


a) perform a pressure leakdown test. If the headgasket is bad the cylinder will fail to hold pressure.

b) look underneath. If the water pump is leaking you’ll see the drip path. A system prssure test is also a good idea. That should expose the leak no matter where it is.

  1. a bad thermostat won’t leak unless the gasket is bad, highly unlikely. A bad T-stat will either prevent the engine from warming up (if it’s stck open) or cause it to overheat (if it’s stuck closed).

Well, 2 things:

If the cooling system has air in it, it will over heat, and any extra coolant that you add to the overflow will get sucked in the next time the car tries to cool off.

If the coolant is vanishing from an internal engine issue, it is going into one of two places:

Combustion chamber is one place. If it goes there, the engine burns it while running. You should be able to smell it in the coolant, or see a large heavy white cloud if there is a lot being burned all at the same time.

Engine oil pan is the other place. You should be able to look at the oil dipstick, and see if the oil looks milky, or too high of a level.

The only other places the coolant can leak from would lead to a puddle on the ground, or all around the engine bay.

One thing that you can consider doing would be to buy one of those cooling system flush kits that you splice their plastic hose connections into the heater core system, and have the cap loose or off as you fill the radiator, and then fill the system the rest of the way from that connection point to eliminate the air pocket between the engine and the heater core.


Thanks much for the replies. I should also have asked – how would I know if the heater core is bad or plugged? The heater seems to work fine if I give it a lot of gas or keep the rpms up. ?

The fact that the heater works fine at higher rpms shows that there is air in the system. At idle or low rpms, there isn’t enough pressure in the cooling system to force water into the heater core, but once it gets past a certain rpm, then the water pump can push water up there.

This is a common issue on a few different Nissan cars, where the heater core is higher up than the engine and the water pump. You just need to have the cooling system bled in a special way to get all the air out, or try the modification I mentioned in my earlier post.