knocking noise under hood?

You said that it sounded like that when you turned it off? None of the choices in the answers above would match that (except one).

What it actually sounds like, is what's called dieseling. That's when the timing is set too low on your car or you don't have high enough octane gas in it. What it does is after you turn the car off, it still has gas left in the cylinders and with the retarded spark, it fires late. So the car tries to continue to run, but doesn't have the steady ignition to do it. What you have is a knocking noise, which is sometimes followed by a "rattle and wheeze" from the engine when it finally quits.

This is also caused, as I said, by too low octane gas. Try plus-grade first and if it still does it, try premium for awhile. It should clear up. If not, get someone to check the timing and reset it to factory specs. It's not dangerous for you car, but it can be extremely annoying. Especially, when it progresses to where the car will continue "knocking" for like 5 minutes after you cut it off!

Check one other thing: turn your radio off and roll your windows up, so that you have quiet in the car. While driving at 45-50 miles and hour, step down hard on the gas. If you hear a "pinging" or "rattling" noise coming from the engine, then it's definitely the timing or the gas.

As for the oil all over the engine, it could be that the valve cover leaks which is also very annoying, but unless you're losing a significant amount of oil from the engine, it's not a major thing, just very messy. (Most older cars have this problem)

By the way, for all you armchair mechanics on here: any internal problems with the engine would cause a hammering or loud knocking noise WHILE the car is running, not when it's turned off. Quit scaring the lady with your total ignorance of how cars with your symptoms act and sound.

Oil all over the place can come from the valve cover cap (where the oil is put in the engine) it may have come off or is loose. You say there is enough oil on the dip stick but you may be seeing water and oil mixed and thus thinking it is full of oil. Look at the dipstick in bright sunlight and look for a milky substance on it. If it looks like that you may have a blown head gasket or leaking intake manifold. A leaking head gasket could blow oil out. If you recently put oil in the engine did you use Engine Oil? I saw a car where the person put Automatic Transmission Fluid in the Engine Crankcase, (a very bad idea) and the engine would not shut off and it was banging and jerking and sounded like it was all over for the engine. Hope it isn't a rod being bent by water in a cylinder.

More than likely it's your valves tapping. Even though there is enough oil in your vehicles oil pan, it doesn't mean that ALL the oil is being circulated through the engine. You may have a clogged oil pump or something, which prevents oil from being shot to the top part of your engine. Lack of lubrication will end up in a seized/locked up engine. Find the jerk who sold you the car & ask them what the previous problems were. If it was a dealership, then you've got them for a lemon law violation.

Sounds like a Timing issue and some moderate oil leaks,as long as you keep the proper oil level,it can leak 'till pigs fly.You can go to just about any quality parts store,tell them the year make and model,they should have a service manual for it.

If it does not velocity up with the engine revs, it must be a loose exhaust or some thing that knocks with the vibration, or in line with hazard the fan hitting the shroud if it fairly is an electric powered fan. i do no longer understand what to do different than to get on the floor, and look below. Wait till the vehicle is chilly, and notice if the exhaust is loose (you will possibly might desire to jack it as much as gain). look on the fan and shroud and notice if there is any sign of it hitting something. yet my funds's on the exhaust. you will possibly be able to additionally be waiting to tell by potential of shaking the tailpipe; in case you pay attention it hitting something, you will comprehend.

You have either a bad connecting rod bearing(ever heard the expression that I just threw a rod?) ; or a bad main bearing.

If you had a bad valve related problem; then you would have a tapping noise instead of a knocking noise. So some of the other answers you received are wrong ! ! !

Instead of looking for a cheap olds book; you should be looking to sell your cheap olds ! ! !

ok a knocking noise can be alot of things try to listen close and an old remidy is to take a stick but watch where you put it put it near where u think the noise is and when it gets louder that will tell u very close such as the water pump or could be a fly wheel or rods knocking or altinater or a pully just put your ear to the stick and listen to pin point noise

you need to give us more specifics on that car. Year, miles, make, model, type of engine.

but it sounds like you blew a gasket and a piston rod OR you snapped a timing belt. None are good news, sorry to say. Basically means the engine is TOAsT.

If the car is over heating , your oil pump has went out or is going out. that will cause your car to knock and it still shows it has enough oil.

I confirm Goyo's answer--and say it's one of the best I've seen. For all you backyard mechanics diagnosing from their computer chairs, STOP scaring the poor lady!