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Oil Pressure Fluctuations- 1995 RAM 2500 5.9L 2x4

Hi Folks… me again, but no Tranny questions here!

I think the wire to my oil pressure gauge might be shorting or loose, since the needle sometimes swings from 0 to the middle unexpectedly for no apparent reason. However, during my recent 350 mile trip back from FL to North GA, I noticed that while “stable”, the pressure seemed to be ever so slowly dropping to the 1/4 area of the meter. I checked the oil level at every stop and it was never more than 1/2 quart from full. It did seem somewhat “black” given that I changed it and filter about 1,200 miles ago. Also, it seemed the oil was somewhat “channeling” on the dipstick… hard to explain, but it wasn’t 100% coating the dipstick like I’d normally expect and seemed like wouldn’t “stick” to it. Anyway, there wasn’t any foaminess that would seem to indicate water in it… and I’ve never used any oil additives.

What can cause reduction in oil pressure? After sitting, it seems normal for a while after start-up but then tends to drop. It is possible there is some kind of “sludge” clogging something? The tranny repair guy told me that some oils contain unacceptable amounts of paraffin (a WAX)… told me to never use Quaker State and that he recommended Valvoline. He was “amused” when I told him I use the Walmart brand… Tech or something in the blue bottle.

Of course, I’ll change the oil THIS week… is that likely to resolve any problems? What else can cause loss of oil pressure? From what I can tell the engine seals are OK since there are never any “puddles” underneath. Any thoughts are appreciated- thanks.

What kind of driving do you do?

Extremely short distances, where the oil doesn’t get hot?

Stop and go?

How often do you change the oil?

How many months and how many miles?

How many miles on the vehicle?

The swinging needle is almost certainly a flakey sensor, gage, or connection, but the pressure dropping as the oil warms is a sign of wear. The oil pressure is developed by the pump pushing the oil through the small small between the bearing surfaces and the corresponding wear surfaces. As the surfaces wear, the spaces become larger and the fluid flows through easier, especially when it warms up and gets less “viscous”, which is a fancy word that means resistant to flow. Pushing warm,. thin oil through larger surfaces, the pump has difficulty maintaining pressure. The oil flows through too easily.

Unfortunately, there’s no simple test for this. A compression test will only indicate the condition of the rings and cylinders, it will not tell you the condition of the critical bearings.

The “channeling” as you’ve termed it, might be dilution of the oil by “blowby”, combustion gasses passing by worn rings. Again, a sign of wear.

What you may want to do is have the oil pressure tested. And be sure to describe the problem completely to the tech, so he can know what he’s actually looking for. If, in fact, the pressure is dropping as it warms up, you might want to try using a higher base-weight oil. That might be just enough to allow the pump to keep the pressure up. On a vehicle this age, I’d be reluctant to invest in a rebuild.

Oh, and the “wax” thing? forget about it. Any oil that meets your manufacturer’s specs and has the API and SAE seals is good oil. And I know Walmart does, 'cause I’ve checked; I’ve used it for many years. And I’ve never worn out an engine, even after hundreds of thousands of miles. I’ll spare you a dissertation on waxes in oils, but ignore that.

Super Tech is not going to hurt anything. Valvoline and Castrol may be the favorite brands but engines have been known to run a long time as long as the oil doesn’t run really low.


Answers… I’m in the “Mountains” of N. GA. Usually 20 - 40 miles per single outing, twice a week WITHOUT the 7x16 very heavy trailer, and then big trips once a month 100+ WITH the trailer. Not much “stop and go”, but LOTS of “up and down”. Truck has 128K miles… and I very recently paid big bucks to have the transmission rebuilt.

the Same Mountainbike

Thanks very much for your reply of 10Feb14 regarding oil pressure on a 1995 RAM 2500 pickup- it was detailed and informative.

When you say that you “wouldn’t invest in a rebuild”, did you mean replacement of a Main Bearing? After watching a video on “low oil pressure”, it agreed with YOU that the oil pump probably is NOT the problem, but rather a worn main bearing. In your estimation, is that a “very expensive” repair? Also, I’m not certain what or even if there is a difference between a “rod” or “crankshaft”, but it was also suggested that the “rod” might need to be replaced.


I will first try using a heavy-weight oil… is 30W about the most viscous? Does this seem like a problem that would occur with 128K miles? I just had the transmission rebuilt (expensive!) and need to decide how to proceed with this oil pressure problem. Does it help to tell you that there is absolutely NO burning smell, no smoke whatsoever in the exhaust or suspicious noise coming from the engine? I will call my mechanic to schedule an oil pressure test… is this something that requires them to drop the pan or anything “expensive”. Perhaps I should FIRST replace the oil pressure gauge “sender unit”, right?

I value and really appreciate everyone’s thoughts on this… now the gauge goes to zero when I stop, then back up to around normal at “speed”. I don’t want to exacerbate a problem if one exists… its just odd that there are NO other signs of problem.


I’d get the pressure checked with a mechanical gauge. Also change the oil and filter and use the thickest oil recommended in the manual. Use a quality filter like Wix or a Mopar filter, not the no-name parts house special. If the mechanical gauge indicates near 0 oil pressure at idle when warm, it’s a good sign that your engine bearings are pretty worn. Your engine is pretty young at 120K to need bearings, but this happens when poor quality oil is used and not changed frequently enough.

As long as the oil pressure gets to normal or close though off idle, you can probably keep driving it indefinitely. Eventually though, the oil pressure will get worse and you will need to rebuild or replace the engine. If you catch it before it gets really bad you can probably get away with just throwing a new set of bearings in the engine without doing anything else to it.

Help me understand channeling, like only on 1/2 the dipstick? You may be picking up residual oil in the tube and not getting a true reading.

Thanks for the follow up post.

A “rebuild” involves more than a bearing replacement. The way the engine is assembled, there is a “crankshaft” that runs the length of the engine to which the pistons are attached via connecting rods, commonly referred to as “rods”. There is one for each cylinder. And where the rod is connected to the crankshaft, there’s “rod bearings”. The pistons slide up and down the cylinders, using “rings” around them to prevent the explosion of the combustion from blowing by the pistons. That enables the explosions to push the pistons down and, since they’re connected to the crankshaft via the “rods”, turn the crankshaft.

The crankshaft itself is bolted to the engine block. It turns in what are called “main bearings”, or “mains” for short. There will be one at each end and one (in a V8) every two cylinders.

These systems contain channels built in to allow oil to be forced by the oil pump to squeeze between the bearing surfaces and the crankshaft surfaces (and rod surfaces) that ride on them. That pressurized film of oil is what the wear surfaces of the crankshaft and the rods ride on. If the space into which the oil is being forced wears too big, the pump can havetrouble maintaining the pressure, just as you’d have trouble maintaining the air pressure in a balloon if there were a hole in it. The “thicker oil” suggestion is worth trying. It might make it a bit more difficult for the oil to flow through the wear spaces and allow the pump to maintain the pressure.

A “rebuild” involves removing the engine, removing the oil pan, removing the engine’s “heads”, disconnecting the connecting rods from the crankshaft, pulling the pistons out toe top, removing/inspecting/replacing/refinishing the rod and crankshaft bearings and corresponding wear surfaces, replacing the “rings”, and reassembling… however, the cylinders need to be inspected and measured with the pistons out and either rebored (if wear is excessive) or honed. Honing is a process that creates controlled scratches in the cylinder surfaces to enable them to hold oil properly and break in properly.

In short, you cannot simply remove and replace a bearing and correct a low oil pressure problem. It isn’t that simple.

I’ll skip discussing the work that needs to be done to the “heads” for a proper rebuild. I hope the description I’ve given has been sufficient to describe the magnitude of the “rebuild” process.

I think the first thing to do is have the oil pressure checked with a separate gage.

Oil pressure sending units like all mechanical devices – especially those w/rubber diaphragms* – eventually fail. That would be my first suspicion, a failed or failing sending unit. You could e ask a mechanic to use a known good shop gauge in place of your sending unit to compare against the reading you get, or just install a new sending unit and see if that fixes the problem. Me, I’d be inclined to the latter of these two options.

I’ve noticed oil sometimes doesn’t uniformly coat the dipstick on my car and truck. Usually that happens if I pull the dipstick soon after the engine has been running. Or if I re-install the dipstick several times during the course of a test. If I look at the dipstick in the AM before the car has been used that day, that isn’t a problem. The dipstick is uniformly coated then, and easy to read.

  • Ever wonder why there is a “g” in diaphragm? English is quite a challenging language!!

If you changed the oil and filter 1,200 miles ago, try just changing the oil filter.

You may have gotten a bad filter with a defective by-pass valve.


Some good info and advice given already. Here’s another vote for replacing the sending unit. If the pressure was truly 0 at idle, the valvetrain, at the least, would have become abnormally noisy. Did you hear any unusual noises?

Good question, George. Perhaps for the same reason there’s a “ph” instead of an “f” in the middle. Language of origin. I think.

@the same mountainbike: "In short, you cannot simply remove and replace a bearing and correct a low oil pressure problem. It isn’t that simple. "

Actually, it is just as simple as that in many cases. Obviously it’s not going to be as thorough as a full rebuild. But if the engine runs well and isn’t burning oil, you can put a set of bearings in it and correct an oil pressure problem in a lot of cases. And if you haven’t waited until the engine is knocking, you don’t have to worry about getting the crank ground or using oversize bearings. (still a good idea to check for wear and out of round though) I have personally done this.

Is it as good a solution as a professional rebuild? Of course not. Is it a lot cheaper and easier than a full rebuild? Most definitely.

Point made, oblivion.

I don’t think the OP understood the situation. I felt he thought it was as simple as just changing a single bearing, and don’t think he understood what was involved in changing bearings. While I don’t support or recommend the approach you describe, I acknowledge it as a possible… albeit 50/50 risky… solution. Might work, but I wouldn’t bet on it. Especially on a 5.9L Ram engine.

Re: Why is there a “g” in diaphragm? TSM replies …

Perhaps for the same reason there's a "ph" instead of an "f" in the middle. Language of origin. I think

@TheSameMountainBike … I did a little research in the Oxford English Dictionary … “diaphragm”, is Latin and Greek derived, first appeared (with an “e” at the end for some reason) in the context meaning a partition in devices in 1665, in a treatise authored by the famous scientist Robert Hook.

From OED

< Latin diaphragma, < Greek διάϕραγμα, the midriff, primarily ‘partition-wall, barrier’

1665 R. Hooke Micrographia : “The Ray…passes also perpendicularly through the Glass Diaphragme.”

As reference to the body part the word first appeared in 1398 as “Diafragma”. In this early version, there is no “ph”, replaced by the more commonsense"f". But no matter what, that damnable confusing “g” remains … lol …

I never did understand English. The rules are all just kind of made up.
Physics is so much more logical. Physics will do what it will do, and it’ll always do it. All we need to do is figure out why. Doesn’t matter what we write as “laws of physics”. The physics couldn’t care less.

OK… so all you guys are totally AWESOME for the great suggestions. “Mountainbike” is correct in assuming that I am a total NOOB… and I truly appreciate how he explains things in reasonably understandable way. I definitely agree that I should replace the “sender” unit FIRST. I’ll “try” to do this myself, since there are good videos and instructions “out there”. Also, I WILL replace the oil and filter with 30W… unless a heavier grade is even available. Summer is coming, so I don’t need to worry about sub-zero temps for the next six months.

Worst case… I’ll talk to “the shop” about replacing main bearing vs. total rebuild. Sadly, I just don’t have a lot of $$ right now, so I need to do as much as I can before hitting the $55/hour help. Going to the shop, if necessary, “armed” with information you’ve provided and the stuff I’ll try first is sure to save them time… and ME MONEY. I owe you all a beer!

PS That green stuff coughed up from your lungs… PHLEGM… why isn’t it spelled “flem”?

You don’t want to use straight 30 weight oil in your engine. All this will do is cause accelerated engine wear at cold starts. Use the oil specified by the vehicle manufacterer.


Thanks for the compliment. I make it all up as I go along…

Let us know how you make out.