2001 sentra 1.8l 179,xxx on the cluster but im told the cluster was replaced so could be more. this is my girlfriends car so i dont really know too much history on it. im not sure if all these problems are related or not so here goes. no heat at idle, every so often it will stumble when started after sitting overnight with heavy gas smell, and on two occasions it did not start for her in the morning the first time she told me she had less the a 1/4 tank of gas so i put 5 gallons in and it started right up the second time i went there after work it went to start then died and started up on the second turn of the key. the cel light comes and goes always with the same code p0300 and runs perfectly once running. heres what i have done over the past 4 month new plugs it had the wrong ones in it they where about a 1/4 inch too short and it did away with all the codes but the random missfire code but it showed no symptoms of a missfire, new batter and alternator, new radiator, and i changed the thermostat to day to try and get the heat to work correctly and it did for about an hour but now there is no heat at all it will go warm for a few seconds then go cold again. now heres the tests i have done cooling system pressure test held pressure for over an hour with little loss of pressure. it also held pressure on its own after sitting for eight hours there was still pressure when i removed the cap. compression test 150, 145, 145, 155, cyliner two is deff flooding, pulled the fuel rail all the injectors are firing and dont seen to be leaking, and there is no fuel coming from the vac line on the fpr someone please help im stumped

 

The thermostat could be stuck in the open position
The heater core could be clogged
The flap that directs the air over the heater core is not properly directing air.
Coolant level is low inside the radiator.
Water pump is not circulating water.

 

According to me, there is some leakage in your radiator distribution lines which are around the engine. Coolant level doesn't matter anymore...

 

turns out it was a head gasket took about 8 hours to do its all fixed