Fluctuating Oil Pressure

My husband and I know very little about cars. We know enough to fill the gas tank, tire pressure, changing oil and other fluids, and that's about it. (We're planning to take an automotive course at the local college come next Spring). Anyway ...

We have a 1992 Chrysler Fifth Avenue that has 120,000 miles on it. The car is actually in great shape and wonderful condition aside from this problem that just started about two weeks ago and now seems to have gotten worse. (Of course, it would have to get worse since we can't afford to take it in for another few weeks.)

A few weeks ago, we noticed this noise coming from under the hood. Now, please forgive my ignorance in not knowing the technical terms for the parts under the hood, but I'll do my best to describe it. (I looked for an image online but couldn't find one :() When looking at the engine from the front of the vehicle, right in the center is this large silver ... er ... thing. For some reason my mind keeps telling me manifold cover but I'm not sure if that is correct.

While the engine is running, it sounds like there is a rock or metal rod being smacked up and down rapidly in there. Closest way I can try to describe the noise is if you were to put metal playing cards in the wheels of a bike so they made noise against the spokes while riding it.

Today we had a 500 miler round trip journey to make but after the first 30 minutes in the car, we decided to turn around and come home. The oil gauge kept fluctuating, pretty steeply too. Before head back home, we pulled into small gas station and checked the oil. It was a quart low so I put in a quart. We waited a few more minutes then hit the road again. We continued to watch the oil gauge but again, it continued to fluctuate. It'd remain in the middle (between the high and low) then would suddenly plummet almost all the way down toward the Low end. Then it'd slowly rise a little, then drop again.

There is no smoke coming from the exhaust. There is nothing else other than what I have just mentioned here in this post. Does someone maybe have an idea of what's going on beneath the hood? If so, is it an expensive repair job? I'm hoping someone may be able to educate me a little here and help me out with information or even suggestions as to what it may possibly be that is causing this.

All responses are appreciated. Thank you :)

The top of the engine is not getting enough oil for some reason. That would account for the clacking which is probably in the valve train somewhere.

It could be your oil pump or even a loose pick up tube at the pump.
A good mechanic will temporarily install his own oil pressure gage and let it run and see what's up.

You probably haven't done any damage to the engine, but I'd drive it around town and as little as possible until you get it looked at. If it gets worse or the gage goes to zero, park it.

Bob

Welcome to AF.

Thank you for all the detail you included on your post.
I would agree that it seems as if the oil pump or the oil pump drive shaft has a mechanical problem.
oil pumps often do not last the life of the engine and, as I recall, on these engines are replaceable without removing the engine from the car.

If the oil pan has to be removed for replacement, I would suggest the mechanic inspect a couple of the crankshaft and connecting rod bearings. These bearings are "plain" that is they are simply spinning metal surfaces which rely on a film of pressurized oil to keep them apart. If the supply of pressurized oil (provided by the oil pump) disappears even for a few seconds, they can become excessively worn or damaged.
If they are mildly worn and/or scored, a mechanic could quite easily polish the bearing journals and replace the bearing shells, while the oil pan is off.

Thank you so much, both of you, for your responses. As I mentioned before, I can't take it in for a few more weeks when we actually have money to pay for the repair, but if it turns out to be what you've both suggested, is this an expensive repair?

Here is a step by step guide to do the oil pump replacement.
http://www.autozone.com/addVehicleId,1755001/initialAction,repairGuide/shopping/repairGuide.htm?pageId=0900c1528005df6e

My guess is a real mechanic would want $500-700 for the work, including parts.

$500 - 700 sounds about right considering it'll tie someone up for 4-6 hours @ around $75 per hour and possibly $100 - 150 in parts. Be warned that other things may come up especially if the bearings need replacement, but expect incidentals like belts, maybe a tensioner.

Which is not bad for a car that age if the rest of it is in good shape and you like it.

Bob

Let me ask you something... is the noise more like a "snick snick" like a sewing machine, or is it more like a "clock clock" like someone hitting the cast iron engine with a hammer?

If its the first, the above responses have it covered. If its the second, you have a spun bearing in the bottom.

Both require attention. Leaving it unchecked may cause MAJOR damage. Put it this way; right now its probably an inexpensive repair. If it drops too much oil pressure and the engine locks up, it means replacing the engine. The added kicker will be that remanufactured engines require turning in your old one as a core. If yours locks up or more damage occurs, it won't be a viable core and you'll have to pay a bunch more.

Unless you can really nail down what is happening, a loss of oil pressure can be a BIG deal. Park it.

Well, I don't know what a snick-snick from a sewing machine sounds like since I don't sew, lol. But, the noise reminds me of a lifter tapping only it sounds more like metal banging against metal. Like if someone where to bounce a metal basketball in place against a metal floor. That's the best analogy I can give to describe the noise.

And thank you all so much for your informational replies. You're really helping a lot.

Well, I don't know what a snick-snick from a sewing machine sounds like since I don't sew, lol. But, the noise reminds me of a lifter tapping only it sounds more like metal banging against metal. Like if someone where to bounce a metal basketball in place against a metal floor. That's the best analogy I can give to describe the noise.

And thank you all so much for your informational replies. You're really helping a lot.

If you really want to pin point the noise, take a piece of wood dowel about 18-24" long, put it to the runninng engine where the noise is and put it to your ear. An old broom handle works great. Like a poor man's stethoscope. Watch out that you don't get mixed up in the belts with it, aside from that it works very well to separate noises out. Put it on things like the alternator and you can hear the bearings running.

I think you're right on the money with it being valve train related.

Bob

We'll try that. But before we do, I'm a nurse so can I just use my extra stethoscope that I have?

We'll try that. But before we do, I'm a nurse so can I just use my extra stethoscope that I have?

They do make ones for automotive diagnostics, yours should work, but take a precaution and pad the end at first with something to filter out the volume, it might be VERY loud.

Bob