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Voltage Meter High AND Oil Issues

I drive a 1995 3.1L V6 Pontiac Grand Am SE.

I’ve been disconnecting my battery often to work on my car. I’ve had a lot of problems with it shutting off on me while driving but after replacing all 3 ignition coils and the crank sensor it seems as though I’ve fixed the problem.

In the process of fixing the problem of shutting off, I had a mechanic replace the alternator. It kept shutting off, so I had the crank sensor replaced because it was throwing a code. It stopped shutting off, so the first mechanic was nice enough to take the alternator off and give me a refund for it when he changed my brakes. With both the replacement alternator and the original/now-installed alternator (which was put in about 2 years ago with a new battery), the voltage gauge on the dash is running high (about 15.5 volts). Before it ran at a steady 13 volts and though the gauge is about 1-2 volts from the red zone, I don’t want to be constantly overcharging my battery. I’ve been told that the voltage regulator in the alternator may be bad, but I find this unlikely considering I noticed the high voltage with both the new and the old alternator.

My understanding is that when the key is in the “ON” but not “START” position, the dash voltage meter reads the battery’s voltage, but when the car is running it reads the alternator’s voltage output. Is this correct?

When it’s reading the battery’s voltage it reads about 11-12 volts. Then when the engine is running it reads about 15-16. 17-18 is the red zone, so that’s why I’m worried. Do you think that the alternator is putting out more voltage because the battery voltage is low before starting (not sure if 11-12 volts is low or not)?

What else could be causing this besides a voltage regulator?

Also: I plan to take it to AutoZone to get the battery and alternator checked but I won’t have the chance to do so for a few days, so some ideas in the mean time, would be much appreciated.

How old is this battery?
Go forth with the planned tests. Expect to buy a new battery.

My alternator died about 2-3 years ago, at which point I got a new alternator and battery.

If I need a new battery, I suppose I can deal with that if that definitely fixes the problem.

I’m just concerned because this car has about 182k miles on it and I’ve put about $600 into repairs in the past month (ignition coils, crank sensor, brakes, rotors) and I don’t want to keep dumping money into it right now. I’m a grad student and have a bunch of expenses coming up and won’t be making nearly as much come May when my assistantship runs out. I have just enough set aside that given my upcoming expenses I could afford a $3000 car and have seen about 3 in my area that have less than 90-100k miles and I’m wondering how much I should keep putting into repairs.

Another concern is that my oil pressure is fluctuating. It used to be steady at 40 psi all the time, and now when I first start it hovers very slightly around 40 but after a bit of driving it goes down to about 25 when I’m not accelerating and climbs about as high as 50 when I am accelerating. I’ve been told that this is normal, especially in older cars. I’m just concerned because it used to always be at 40 psi and now it’s not.

You’re correct about the battery voltage readings with the key on/engine off and while running, etc.

The 15-16 volt charging rate is too high. If the problem is not related to the voltage regulator then it could have something to do with the circuit between the alternator and battery or a junction terminal problem.

The former could be a blown fusible link. The latter could be corroded connection at the junction terminal. There should be a smaller wire cable from the battery positive terminal leading to a threaded stud that should be under a plastic cover near the battery. All electrical power except the starter motor windings go through this terminal and a poor connection could possibly lead to an alternator charging a bit stupid. It can also cause an engine to quit intermittently or not start on a random basis.

What needs to be known now is what the charging voltage is at the battery itself when the engine is running.

The engine is tired. That’s why your oil pressure is wavering. As the engine wears, one of the side effects is that it has greater difficulty maintaining oil pressure at idle. And before you ask, it is NOT repairable by replacing the oil pump. The problem is wear surface wear, not the oil pump itself. You can try a higher base weight oil. Might help, might not. Can’t hurt.

Buying any vehicle in that price range will carry risks unless you know its history. Unless you’re buying from a relative, IMHO you’re better off to keep the $3K and use it as necessary to keep the ol’ Pontiac running. Better a known safe vehicle with a bit of old age symptom than a vehicle with a high potential for hidden problems some of which might be safety related.

I don’t have a multimeter or anything to test the charging voltage. Is this something AutoZone can test for me?

Also, I noticed that the bolt that locks the cable to the positive terminal on the battery is a bit stripped. When I tighten it, it’ll slip past and go loose and I have to re-tighten it into its sweet spot (does this make sene?)? I know you’ll be inclined to tell me I’m an idiot for not replacing the bolt earlier (rightfully so) and probably also inclined to diagnose that as the problem. But I always make sure that the bolt is tight when I’m done. Could this be causing the problem?

It could be. If the connection is high resistance, the voltage as measured by the gage will be low. The good news is that the bolt is easy and very cheap to change. Mention it to the tech that tests your battery and charging system.

Don’t for a moment think you’ll be judged for anything you say or do (or don’t do) about your car. I and many others here learned long ago not to judge others. I may know a bit about cars, but your subject of expertise is probably one that I’d be totally ignorant in. And believe me, there are a LOT of subjects that I’m totally ignorant in. We’re here to try to help, not to judge.

Besides, idiots don’t ask questions. They assume they already know everything. You’ve already proven you are no idiot.

Post back with the test results.

Go to Harbour Freight and get yourself a digital voltmeter–they are only about $5 these days. In fact, they just offered a coupon for a free one with any purchase I think. It’s not going to be the quality of a $300 Fluke meter, but the price is right and they are surprisingly accurate. (and expendable) Everyone should have one in their toolbox.

Check the voltage at the battery with the meter and see if it matches what your dash gauge says. If the dash gauge is accurate, I would suspect one of 3 things are wrong, as other people have pointed out:

-Your battery is weak and causing the alternator to run at full output to try and charge it.
-The regulator (whether in the alternator or handled by the ECU) is bad.
-You have a bad ground or other connection somewhere–either at the alternator, at the battery, or possibly at the ECU if it regulates the voltage.

Charging at this high a voltage is not good for your car’s electronic systems and I would correct it as soon as you can.

Everyone is steering you right! Make sure all connections are clean, corrosion free, and tight. Make sure the grounds on the engine and chassis are clean of rust and tight.

I’m leaving to go to AutoZone in about 45 minutes. I’ve never used a multimeter before, so I’m apprehensive that I won’t be taking accurate measurements.

Can you guys coach me through exactly what I should ask the tech at AutoZone to check? Also, are they generally pretty patient and willing to test multiple things on your car? Will they try to sell me something I don’t need?

My mechanic is very backwoods and though sometimes after taking my car there, the problem isn’t fixed, they never dupe me into replacing something I don’t need to.

They test the charging system with an automatic device that loads the battery and test the alternator output. Bad or loose cables can cause the alternator to put out to much voltage. A multimeter is easy. Black lead on the black battery cable and the red lead on the read battery terminal. It will then display the voltage of the battery. If the car is running it will show the output of the alternator.


Buy a set of those side terminal bolts at your local Autozone. It may very well be the end or your problems

More than likely the threads in the battery are striped.

The bolt is made of steel. The threads in the battery are in lead. So the threads in the battery will strip out before the bolt.

Replacing the battery so there’s good threads where the bolt can be fully tightened may get rid of all the electrical issues.



We have tons of GM side terminal battery vehicles in our fleet

It has been my experience that the battery bolt threads strip, and the internal threads in the battery itself are fine

We stock those battery bolts, for good reason

I’m not saying you’re wrong

I’m just speaking from experience

Okay, I’m kind of freaking out right now. Let me give you a run down of what happened.

I went to AutoZone, they tested my battery and alternator and said that I needed a new battery. I installed a new battery and terminal bolts. The voltage gauge on the dash is still reading high (about 14.5-15.5 volts). So I ran to Walmart and bought a multimeter.

As I was going through town to go home (lots of traffic and red lights), my car was running hotter than usual (200 degrees when it normally runs about 150 degrees or a little less). The oil pressure was going down to about 10-15 psi when I was idling and up to 40 psi when I was accelerating.

I started the car back up after getting gas and the thermostat was reading about 15 again and my oil pressure was a bit more normal (about 20-25 idling/not accelerating and about 40 when accelerating).

When I got home, I noticed my engine smelled funny (almost like burning rubber, but I know I wasn’t stressing my brakes or anything). Then I noticed that there was black crud that was a little wet to the right of where I put oil in my car. I’ve attached a picture. It seems to all be right around where that cable plugs in.

Another notable thing is that when I turned off my car at both the gas station and when I got home, the oil pressure gauge nor the temperature gauge dropped to zero. I’m not 100% sure but I think they normally do drop with the rest of the gauges when I turn the car off.

I used my new multimeter to test the voltage with the car on and off. My battery is putting out 12 volts and my alternator is generating about 13.6 volts.

Any insight into the oil pressure/temperature issue or the voltage issue is much appreciated!!!

Is that most likely oil? I’m not 100% sure. And as far as I know, burning oil is a very bad sign.

Where you see the oil is the PCV valve. Remove the PCV valve and try shaking it. It should rattle. If doesn’t rattle replace it.

The coolant temperature fluctuation is from a bad thermostat. The thermostat is rated at 192 degrees. This means that the thermostat doesn’t open until coolant reaches a temperature of 192 degrees. Once the thermostat opens, then it’s up to the cooling system to keep the coolant temperature under control with the water pump, radiator, and fans. Once the thermostat opens, the coolant temperature can rise to 210-250 degrees. Depending on the ambient temperature.

The oil pressure fluctuation can be normal on an engine with a lot of miles on it. The rule of thumb is there should be 10 PSI of oil pressure per every 1,000 RPM’s. Or. the by-pass valve in the oil filter is malfunctioning.

On the charging system, with the engine off the battery voltage should be 12.5-12.7 volts. When the engine is started the alternator should be putting out 13.5-14.6 volts.

So, from what you’re describing, the PCV valve should be replaced. The thermostat should be replaced. Try replacing the oil filter to see if that fixes the oil pressure reading. If not it could be normal if the engine has a lot of miles on it. On the battery/charging system? Drive the vehicle for a while to see if the battery voltage stabilizes at 12.5 volts or greater.


What Tester said. I think that you’re suddenly being hypersensitive to things. 13.6 out of your alternator is just fine. That black sludgy stuff has been there/building up there a long time. The oil pressure behavior sounds perfectly normal to me. It’s supposed to drop at idle and go higher when you accelerate. What you said about the temp is that it used to read 150 degrees but now is up to 200. As Tester described, 200 is normal. 150 is too low.

Anyway, I think you’re suddenly hypersensitive.

I have 182k miles on my car, so I guess I should just accept the oil pressure fluctuation. It just worries me that it got down close to 10 psi today. My oil and oil filter were just replaced two days ago.

My car is still a little warm. I just turned it off about an hour ago. Is it safe to take off the PCV valve while my engine is still warm?

Sorry for my ignorance and my determination to work on this myself. I just don’t want to spend any more money taking it to the mechanic.

If the engine has been off for an hour, you can remove the PCV valve.