Just driving down the road today and noticed oil pressure gauge suddenly drop to 0. When accelerating, the gauge goes back up and then back down to 0 when driving at steady speeds. Also, in Park and I press accelerator, gauge goes up...until I let off the pedal, then goes back down to 0. What is going on?



1997 Ram 1500 SLT Club-Cab
4x4, 5.9L, LT285-75-16 Michelin's

Now that sounds like a sending unit failure, eather that or your out of oil.

Yeah, sending unit; unless you're getting dangerous noises from under the hood.

No bad noises and oil level is fine. Where, exactly, is the sending unit sensor under the hood?

I think it's found at the rear of the intake manifold to the right side of the distributor.

I think it's found at the rear of the intake manifold to the right side of the distributor.


To: fredjacksonsan. I have a '98 Dodge Ram with a fluctuating oil
pressure gauge. I wonder what it could be? The
sending unit or oil pump? I want to try to take the
sending unit out and install a hand held pressure
gauge to see if it fluctuates on it. What do you think
it could be?

Thanks,
Steve.

Does it fluctuate between driving and idling, or does it fluctuate while the engine is at a steady speed?

I think it fluctuates between driving and idling. That is when I notice it. It drops sometimes to just below 40 and then goes back to about 50 or 60. Sometimes it does not change at all at idle. I noticed yesterday it did it when I put the brakes on.
Any clue will help. No noise from the engine. Should I worry or just let it be?
Thanks for the reply.
Steve.

I think it fluctuates between driving and idling. That is when I notice it. It drops sometimes to just below 40 and then goes back to about 50 or 60. Sometimes it does not change at all at idle. I noticed yesterday it did it when I put the brakes on.
Any clue will help. No noise from the engine. Should I worry or just let it be?
Thanks for the reply.
Steve.

Also I failed to mention that it has 175,000 + miles on the engine.

With that many miles, some fluctuation may be expected. I've had both 318's and 360's (5.2/5.9) and after many miles they too had some fluctuation in the oil pressure, most notably at idle.

A new oil pump will likely solve the problem, and IMO certainly can't hurt if you intend to keep the vehicle.

As long as it's steady while under load you should be ok. And 40psi at idle sounds like it's enough, but dont' quote me on that.

Thanks for the info on this. I think that I will eventully put a new oil pump on as I plan to keep it for a while. Like you said, it won,t hurt. I wonder if I should try using an oil for higher mileage?

Can't go wrong with synthetic for your engine. Runs cooler, might give higher mpg.

Thanks. I will use the synthetic on next change. I need to get better gas mileage. I estimate at about 10 - 11 mpg. I would like to get some ideas as to make it better.
When using synthetic will I still go by the same weight of what it is now?

Yup, same oil weight for sythetic as recommended by the manufacturer.

Is the inside of your tailpipe black and wet? If so, you might have a bad O2 sensor, which would cause your truck to run rich. With overdrive you should be getting a bit more mileage (unless you put on larger tires than stock)

To: fredjacksonsan. Yes you are right. I checked the tail pipe and it was black and had water in it. I will check into getting the O2 sensor repaired. I do have bigger tires. They were on when I puchased the truck. They are 285- 16 and I checked as to what they are suppose to be. They should be 245. I wondered if tire size would make a difference in gas mileage.

fredjacsonsan: How many 02 sensors do I have? It is single exhaust. I've been reading up on them and you are right. It will make the vehicle use more gas. I will change them out.

Thanks for the info. You are a big help to me.

Steve.

fredjacsonsan: How many 02 sensors do I have? It is single exhaust. I've been reading up on them and you are right. It will make the vehicle use more gas. I will change them out.

Thanks for the info. You are a big help to me.

Steve.

I failed to mention that I have the Haynes auto manual for this truck.

Steve, you're welcome; glad to help out. A lot of the info I'm passing to you I've gotten on this site.

In any case, glad you figured out the O2 sensor; it's an easy replacement, a plug for the electrical and unscrewing the old one (but the old one may be in there quite tightly).

Larger tires often cause lower mileage for two reasons:

1) Harder to turn, engine works harder

and

2) Less revolutions per mile, so your odometer registers less miles traveled for the same distance, so it throws off your mpg calculations.

Keep in mind that tire height is what's important for the mpg consideration. If you have 285/xx/16's, what is the middle number (aspect ratio)? A tire with a 285 width can be the same height as a 245 tire.

Check these out for tire size comparisons. The first one also gives you the % that your speedometer and odometer will be off:

http://www.1010tires.com/TireSizeCalculator.asp

http://www.dakota-truck.net/TIRECALC/tirecalc.html

Oh yeah, and for the O2 sensor(s) look under the truck, near the catalytic converter(s). I think there's only one on your model, after the cat, but there could be one before and one after. Also, if you have 2 cats then you'll likely have the same setup both sides.

Just getting under there and looking will give you your answer; sorry don't know for sure.

Hey fredjacksosan. I've changed both 02 sensors today. I hope I get better gas mileage. Two sensors cost me about $125.00. I hope it is worth it. My wife asked me how they had cost and when I told her she was like " how much"!? As for the tires, well I don't know for now.

Thanks for the feedback.

Steve.

Sure thing...

My 96 318 Did The Same Thing...i Replaced The Sending Unit And Havnt Had A Problem Since

Just to update fredjacksonsan: It seems that my truck is running a lot smoother since I changed the 02 sensors. Before it seemed to have a rough idle. Now it is more of a smoothe idle. Later I will change the oil pump and see if my gauge problem goes away.

Thanks again!
Steve.

Just to update fredjacksonsan: It seems that my truck is running a lot smoother since I changed the 02 sensors. Before it seemed to have a rough idle. Now it is more of a smoothe idle. Later I will change the oil pump and see if my gauge problem goes away.

Thanks again!
Steve.


To pissedriteoff: Didn't that sending unit set you back a bit? I was going to do that to my '98 360 until I found out it cost $34.00. I guess though you have to do the proccess of elimination. I am a maitenance worker and I have to do that on my job sometimes.

Sharter.

Sending unit's probably a lot cheaper than a new oil pump. Easier switch, too.

Got the new sending unit today, along with the socket to fit, for 34.80 at NAPA. Getting ready to change it out now, let you know how it went.

:thumbsup: Hope that solves the problem. If not, you've got a new sending unit. (One advantage of replacing things is that you usually don't have to ever replace them again)

That is true. When I first bought my truck The battery was dying on it. It was a fairly new battery so I had it and the alternator checked. Battery was weak and and alt was good. Then I charged the battery and it lasted about a week then dead again. So I had all checked again and the guy at the parts store said that my starter may be pulling down the batt. So I bought a new starter. Well Same problems again. So I consulted an alternator shop and he told me that I had a short somewhere.
I began pulling fuses and when I pulled them at the main box under the hood I found the problem under it with naked wires. I taped them up and no more dead battery. So I ended up with a new starter.

Okay, changed out today. Gauge is working steady again, but I noticed that when my truck is idling, the pressure is reading about 30 or little more maybe and when driving down the road, it's showing 40-45. Before the old gauge started flopping around, it always stayed around 40-45. Is this a problem or just a good reading again since the sensor was going bad before? Oil level is fine.

Sounds like it's reading right. A drop in pressure is to be expected with an older motor. It still wouldn't hurt to replace the oil pump; but if the pressure goes right back up to 40-45 as soon as you hit the gas, I would drive it that way.

Just out of curiosity, how tight should the oil pressure sensor be tightened down when you put it in. Not to sound stupid, but I snugged her down pretty good when I did mine.

Sorry, but I don't know the torque specs.

Just tight should be good enough, no?

Yep, my backyard mechanic built-in torque wrench says, "Tight, but not TOO tight".

:D

snug and not too tight is good on that, if you ever need to replace it again, and its too tight, it will probably break. oil pressure is lower at idle than at operating rpms. it should never go under 20 or over 50, if it does, you got some problems.

Thanks, guys, then everything is doing just great.

To fredjacksonsan: Hey man. Haven't talked to you in a while. It seems my oil pressure gauge has settled down a bit. It is not as erratic as it used to be. I've done nothing to it. I'm thinking of trying some engine cleaner or flush. Maybe the screen on the oil pump could be a bit stopped up. Just a little update for you. Everything else seems OK for now.

Catch ya later.

To fredjacksonsan: Hey man. Haven't talked to you in a while. It seems my oil pressure gauge has settled down a bit. It is not as erratic as it used to be. I've done nothing to it. I'm thinking of trying some engine cleaner or flush. Maybe the screen on the oil pump could be a bit stopped up. Just a little update for you. Everything else seems OK for now.

Catch ya later.

Yeah hey, what's up? (sorry bout temporary thread hijack)

I'm thinking there could have been some impurity or clog at the entrance to your pressure sensor. Maybe if you take it out, clean it, and reinstall it would settle down?

(I hate intermittent problems, they're frustrating)

/temp hijack