What would cause air to blow back out of oil filler cap while running 2001 nissan altima

Yes, perfectly normal. The top of the engine is connected to the bottom of the engine by holes that allow the oil which it pumped under pressure to the valves and rockers to drain back to the sump. In the bottom of the engine you have the open cylinder bores with 4 pistons running up and down 1,500 times per minute (rpm). This creates a lot of air movement and why the has to be a breather. No one ever take the oil cap off with the engine running!

Possible causes Missing or loose fuel cap Incorrect fuel filler cap used Fuel filler cap remains open or fails to close Foreign matter caught in fuel filler cap EVAP canister or fuel tank leaks EVAP system hose leaking Fuel tank leaking

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If you mean oil coming out of oil cap the answer is No

there will be,if it shoots the cap off while you are unscrewing it then you might have an issue,but oil will come out with car running and cap off

You could possibly have air trapped in the heater core. The easiest way to bleed it out is to jack up the front of the car till the radiator fill cap is higher than the upper heater hose using a funnel that fits snuggly in the filler neck of the radiator, fill till you have about three inches of coolant/antifreeze above the filler neckthen run the car at about 1500rpms until no more bubbles are evident. Also turn the heater onto face on low speed and feel if heat starts comming out.

You will need R134a, and a filler hose. Charge the system on the low pressure side, it should have a blue cap on the charge point.
Your filler hose will only fit the low pressure side, just in case the cap has been removed.

Hi!
It appears we have an Air lock scenario and you will need to perform a system Bleed.
Park the vehicle on level ground, when cold remove coolant filler cap, start engine and leave to idle, turn heater on full and blower to max. When engine reaches operating temperature watch and listen near coolant filler, keep clear as gurgling and hopefully a boil over should occur. Top up with very warm coolant and wait as it may do it again.
Check for heat inside vehicle if warm replace coolant cap but keep an eye on temperature gauge as the ~Air lock may have moved on from heater matrix/core so proceedure needs to be carried out again from COLD.

Please press the Blue button to appraise my FREE Efforts, Thank You!
Paul 'W' U.K

Hya!
You need to bleed the cooling system.
To do this park on level ground, when cold remove coolant filler cap, start engine and leave to idle.
Have plenty of warm/hot water available, when engine reaches operating temp it may appear to boil over so keep away from coolant filler, top up with warm/hot water and wait as it may bubble over a few times before settling.
Replace cap and hopefully back to normal, Remember your Anti Freeze?
Good luck,
Paul 'W'
Oner~EDson(:0) {#><U.K.