If I loosen the oil filler cap on the V6 in our 2001 Gallant there is a great deal of air pressure internally. Feels like a pulse when the cap is completely removed.

Is this normal, and if so does anyone know why? Every motor I have ever seen ran with a vacuum connected that kept negative pressure.

Just a little confused,

Thanks

 

yea, thats normal, the engine requires pressure to circulate the oil from the crank case / oil pan to the valve cover, if your worried about to much pressure built up you might want to make sure to replace your PCV Valve. To much pressure built up in the crank case case is caused by blow by or compression leaking around the pistons in the cylinder, which is then caused by foreign objects (pebbles, metal shaving) inside the cylinder wearing away crevasses in the cylinder wall.