Ok, so this is what I have been noticing, and I would like to know if anyone has any thoughts or ideas. I thought my little vehicle was doing better, but unfortunately it still has a similar problem. I will give you all of the symptoms and see if anyone can diagnose this problem. The radiator fluid reservoir tank has a leak in it, and I am currently waiting for the replacement, when I start the vehicle there is a clanking sound as it runs. I checked the oil and it appears to be low, and there is no leak at the oil pan or the oil filter area. Oil still seems to be coming out of the oil filler cap area even with a small whole in the filler cap to relieve some pressure. As you drive down the road the speedometer will start going hay wire, for example jumping from 40 mph down to 20 mph to 30 mph to 40 mph etc. At first I thought the speedometer problem was due to the speedometer itself being faulty, but replaced the speedometer with a new one, and it still jumps all around, but when the car is in cruise control, the speedometer will start to go haywire but it also sounds like the engine is also going haywire along with the speedometer. When you make a turn, the oil light on the dashboard will illuminate and will go out when you start driving straight again. The vehicle now has a hard start up in the mornings, where I will try to start it at first, and it wont turn over, but second time is the charm. Any thoughts will be much appreciated.
“I checked the oil and it appears to be low”
Can you elaborate? How low, and what did you do?
“clanking sound as it runs”, that could indicate major engine damage, specially if you let the oil run low.
Re the speedo, it probably runs from an output on the transmission. the real mechanics here will probably comment further. The engine sounds while in cruise control is due to the bad speedo. Don’t use cruise control until you get this fixed.
Put A Fork In It?
Sorry, but that’s my first instinct, here.
It seems that that this vehicle has more problems (some possibly catastrophic) than one should consider fixing on an 18 year-old car.
Without knowing about the engine condition (blow-by & knock/rattle), the PCV system, the speedometer (speed sensor?) problem, engine going haywire, dashboard illumination, starting problem, etcetera, it’s only my guess.
This car cannot be operated low on oil! That’s for sure!
CSA
Hex? Consider yourself lucky that this rig is even moving. Or was. Usually a neon has a 4 yr life before the junkyard.
Try changing your PCV valve, but don’t get too optimistic.
My guess is that the clanking sound is bearing knock and the oil coming out of the oil fill cap is due to blowby, a term that describes combustion gasses blowing by the piston rings. That blowby pressurizes the crankcase and, if extreme, can cause enough pressure to force oil back up the return paths through which it normally runs back to the crankcase after lubing the camshafts.
In addition, if you’re losing oil and it isn’t leaking, it’s burning. That happens because the cylinders and oil wiper rings are worn, the rings’ tension is tired (that’s what pushes it up against the cylinder walls), and perhaps the rings are gummed up with crudded up oil gump.
The oil light coming on when you corner is because the oil is being allowed to run low. That may also be the reason the engine is shot. The system maintains pressure by drawing oil up from the pan through a straw-like “pickup tube” the end of which needs to remain immersed in oil. When the oil is allowed to go too low, the oil going up against the inner wall of the oil pan from inertia lowers the level below the pickup tube and the engine is essentially starved for oil.
In short, all of your symptoms together add up to a worn out engine. Sorry.
I’d do a wet/dry compression test, but I suspect it’s academic at this point.
To elaborate on the low oil finding, I would fill up the engine with oil in the morning and by mid-afternoon, the oil would be low already, and there would be oil all over the reservoir cap as though it was pushed out of the engine from that spot. I know that is where the oil is coming from, because I wipe it all down to as clean as possible, and in mid-afternoon it is full of oil again.
You are getting excessive pressure in the crankcase and that is pushing out the oil. Simple solution might be the PCV valve, so change it of clean it in solvent.
More complex problem could be your compression rings are worn and allowing compression to blow by the rings and that adds pressure in the crankcase. Solution is an engine tear down and rebuild that isn’t really cost effective in an old Neon. It then becomes an add oil and run 'er till she won’t run anymore scenario.
Have you ever hooked up a mechanical oil pressure gauge, when the engine had the proper oil level, that is?
Have you performed a compression test?
Hooked up a vacuum gauge at idle?
None of those will take long, and it will tell you a LOT about the mechanical health of your engine
How long has this situation been going on . . . ?!
To elaborate on the low oil finding, I would fill up the engine with oil in the morning and by mid-afternoon, the oil would be low already,
Can you elaborate on that? How many quarts? Are you using the dipstick or just filling up the engine? Driving from morning to afternoon could be 600 miles, how much driving?
First I would follow those who have suggested to change the PCV valve. They are inexpensive and easy to replace!!!
Second, if you need a quart of oil…add it. Don’t drive and find that the oil light goes on in turns. It goes on because you need oil. If the light goes on, pull over and add whatever the dip stick indicates it is low. The low mark and the low oil light does not mean “add oil sometime in the next week”.
I’m unsure what you mean by the “clanking on start up”. This could be evidence of the lower end being starved of oil at some point, or it could be as simple as a loose heat shield. Or as in my truck, a loose baffle in the exhaust resonator.
If you have run it extremely low on oil before, you most likely have ruined the engine beyond repair. Or at least beyond what the car is worth.
The hard starting may be a mistake in terminology. You turn the key, the engine cranks (turns over) then it either starts or it doesn’t start.
If it turns over but has a hard time actually starting , the rings may be weak from a oil starvation episode and the compression is low. The compression may be just at that edge where it may start…or it may not. Weak rings again would not be worth the expense of fixing this.
If you turn the key and it does not turn over (as my description states) then you most likely have bad connections at the battery. Remove the cables, clean the posts and terminals with a proper Battery post & terminal brush and re-tighten the terminals.
Third, the jumping speedo is most likely from a corroded plug in the back of the speedo or at the VSS (Vehicle speed sensor) on the Transmission. Check and clean the connections…it may even just be loose.
Yosemite
Someone must have put a hex on my 1998 Plymouth Neon</b
Yeah, Chrysler
While I’m not a Mopar fan (never cared for their styling), in this case it sounds in reading the thread like the engine was hexed by oil neglect. To me it’s important that the OP understand the part that neglecting the oil level (or other problems) could have played in the current problems. Understanding that could prevent a whole lot of future problems in his/her future cars.
The crankcase – that’s the part that holds the oil – is designed to have a partial vacuum when the engine is running. So one quick test you could do, remove the oil filler cap, start the engine, and hold a piece of paper (8 x 11 or at least big enough it won’t get sucked into the engine, be sure to hold onto it) over the filler hole. The crankcase vacuum should hold the paper tight against the oil filler hole. If it doesn’t, there may be something wrong with the crankcase ventilation system, possibly a faulty pcv valve. Not an uncommon thing, and easy to fix. As mentioned above, there’s other more expensive possibilities too.
I wouldn’t be surprised if the problems on this engine don’t extend FAR beyond a pcv valve
And I’m not blaming mopar
I’d be surprised if they DIDN’T! But for $6 it’s worth a shot. There’s a .00000745% chance I could be wrong. 
Truth is, a gummed up PCV valve won’t cause the clanking, the occasional oil light when turning, and only too much blowby could force the oil past the fill cap.
mountainbike
I agree with you and all the others that a pcv valve should be the first step on this engine
In fact, don’t even bother to test it first . . . just replace it
Certainly sounds like there’s something amiss with the pcv system. Meaning perhaps the valve isn’t the only problem
To elaborate on the low oil finding, I would fill up the engine with oil in the morning and by mid-afternoon, the oil would be low already,Can you elaborate on that? How many quarts? Are you using the dipstick or just filling up the engine? Driving from morning to afternoon could be 600 miles, how much driving?
@Nevada_545 Your reply gave me the sick image of the OP filling the oil until it reaches the top of the valve cover.
I replaced the PCV valve along with the hoses with all new parts. What I meant by the filling up the engine with oil is that I drive 10 to 15 miles a day, and I check the oil in the morning when it is cold, and the dipstick indicates it is up to the proper markings, when I check the oil in the mid-afternoon, I make sure it has completely cooled before checking, and when I check the oil level the oil level is below the add-quart mark. I make sure the oil is at the proper level everyday, and I am doing my best to make sure that it does not get too low to cause any engine damage, but the cost of replacing the oil almost everyday is getting costly. I took the car to a local mechanic and he told me it might be the water pump going out, the oil pump, or another internal problem.
You have to add a quart every day after 10 to 15 miles of driving? There has to be a major oil leak somewhere.
The water pump would not be the problem. The oil pump could cause low oil pressure, but not a large loss of oil unless a seal was leaking. Then you would find a puddle where you park.
What is the history on oil changes on this machine.How many miles between changes. And how many miles on this thing.
Yosemite