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oil pressure low

jfabert

jfabert

1/2 ton status
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South Ogden, Utah
to start off its a 87 350 176k miles. i have never had pressure issues before but during a 250 mile trip when I stopped in traffic I noticed my oil pressure at about 15. before this after it warmed up it would only go as low as 20 at idle after a long run. now after only a 10 mile drive on the freeway at idle it is getting around 10 or less and at cruising speed its 30ish. its not really consistent either at times. when its cold it will be at 60 and other times around 30. I did replace the sending unit about 6 years ago cause it was leaking. also the truck sat for a year while i was gone and my wife would start it up every month and warm it up but when i changed the oil after i got home it had some chunks in it. i ran some seafoam in the oil for about 600 miles then changed it again. it runs fine and i dont have any noises from the motor. i have read on here to use a manual gauge to check the pressure and see if they match. i was just going to replace the sending unit again just in case it got a chunk of crud in it and turn the motor over with it removed to flush out the fitting then get a manual gauge if it stayed the same. could I have spun a bearing and that would be causing this and could i check that with out pulling caps on the crank. and if i did how long can i expect the motor to last just driving 20 miles round trip to work. i moved for work so i dont have another vehicle right now and need to figure this thing out. any tips would help. also i have always used 10w30 oil in it.
 
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Could even be the gauge itself.

Even if it is only readin 10 psi hot idle...it could still go a long time. The engine 'needs' 10 psi per 1000 rpm as a minimum.

Rene
 
Make sure your temp is not acting up, varying temperatures will affect oil pressure.
Always double check a pressure problem with a mechanical gauge.

Unlikely you have spun a bearing without hearing something.
If it is a mechanical problem, since it comes and goes, I would be suspicious of the pressure valve in the oil pump.

When you say chunks.......Chunks of what? Metal would be a bad thing......

Also, slightly related, check your muffler and exhaust pipes. I'll bet that the metal is paper thin if not full of holes.

I hate to say it, but depending on how she did it, your wife might have done a lot more damage than if you had just let it sit.
Engines produce acids when they run. When the engine is cold, this acid accumulates in the oil, and passes out the exhaust as vapor.
Starting a cold engine produces lots of these acids. And fills the oil and exhaust with them.
Running the engine until it says warm, does not boil them out.
The engine has to run at operating temperature for a good period of time for them to get out.

On a cold day, you can see liquid dripping out of the exhaust for quite some time after the engine is up to temp.
The chunks were probably sludge caused by lots of moisture built up in the oil.

I would change the oil and filter again and watch to see if it comes out normal.
If so, consider switching to a synthetic, maybe in 10W40 or, better yet, 20W50.
The synthetic at that weight will still cause less friction than your regular oil at 10W30, and will maintain pressure much better.

Putting a synthetic in an older engine should not be a problem. I switched my truck at 180K, and still had plenty of pressure at 250K when I swapped the engine because of a warped head.

Plus my 1948 8N tractor loves the stuff.
 
yes it was sludge that came out. it looked it had built up on top of the oil. i did replace my t-stat last weekend because it was starting to stick. i was thinking that would be the cause of the low psi when it was hotter but the psi is still low and the temp is normal. ill take a look at the pipes tomorrow after work. so will any manual oil psi gauge from the parts store work to check it with or should i be using some other type. ill try the heavy weight synthetic oil also this weekend. thank you.
 
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I would replace the sending unit just in case the sludge has affected its ability to read accurately. I used to have an E350 van that needed a new sending unit once every 18 months or so, and I knew it needed replacing when it started showing symptoms similar to what you're describing.
 
We frequently cut open oil filters to learn more about the condition of the engines we are servicing. There is a cutter made specifically for this, kind of like a tubing cutter. If you have bearing problems it will show up as fine metalic particles.
Kurt
 
The 350 I had in my '72 K5 years ago would show a huge drop in oil pressure after a long ride (like my 1.5 hr commute to work each day!) when I'd stop at the end of the exit ramp after a 70 mile highway beating...I noticed it a lot more when I changed the oil to Amalie 10W-30..I was not happy to see the gauge drop below 10 psi at idle and only hit 35 at speed,where I used to get no less than 20 psi at idle hot,and 40-45 lbs at 2000+ rpms..this had an aftermarket mechanical gauge,I even tried another one in case it was the gauge lisleading me..but it was OK,and I blamed the oil..

I changed the oil to Castrol 20W-50 and the pressure returned to its usual readings,no more dropping to near zero after a long ride..I assumed different oils have different viscosity at high temps,and evidently the Amalie had viscosity breakdown a lot more than the Castrol did..I stuck with the Castrol and never had any engine troubles as far as lube related...other guys I've talked with have had similar results when they started using cheaper oils ,and they went back to Castrol or synthetics ..
I noticed using a 2 qt oil filter on my Blazer helped the oil pressure stay higher ,probably because it helped cool the oil more,and cooler = higher viscosity..
 
thanks guys for the help. i have always used regular Mobil oil in it and this last time i used Mobil Clean 5000. i will try out the 20w50 synthetic and see what happens.
 
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jfabert said:
thanks guys for the help. i have alwase used regular Mobil oil in it and this last time i used Mobil Clean 5000. i will try out the 20w50 synthetic and see what happens.
Click to expand...

didn't know they made a 20/50 synthetic, the thickest i have found so far is 10/40 :dunno:
 
I used regular Castrol,not synthetic..that was back before we HAD the choice between the two!..I think regular petroleum oil has more viscosity and stays thicker than synthetic does,I've seen engine with high mileage lose quite a bit of pressure when switched to a synthetic,but regained it when the owner went back to the regular oil he had used before...I'd stick with regular oil in a high mileage engine that has some wear,maybe add some LUCAS or Marvel Mystery Oil Oil Stabilizer to give it some additional viscosity and wear protection..
 
:D
diesel4me said:
I used regular Castrol,not synthetic..that was back before we HAD the choice between the two!..I think regular petroleum oil has more viscosity and stays thicker than synthetic does,I've seen engine with high mileage lose quite a bit of pressure when switched to a synthetic,but regained it when the owner went back to the regular oil he had used before...I'd stick with regular oil in a high mileage engine that has some wear,maybe add some LUCAS or Marvel Mystery Oil Oil Stabilizer to give it some additional viscosity and wear protection..
Click to expand...


this is something i watched closely with my two trucks here when i switched them to synthetic, the one truck has over 225k miles on it, with no major mechanical problems in it's life, still doesn't burn any oil, may leak a tad, but in the, so far, 4000 miles we've driven it with the synthetic 10/40, it's only down about 1/4 quart. The pressure gauge did act alittle weird at first, but i blame the sending unit, not long after, it steadied out and has been around the 45psi mark most of the time, alittle higher when cold.

My Burb has a brand new motor in it with less than 5000 miles now, i switched shortly after the break-in period and the pressure is about the same in that one, with being alittle higher when cold.

There was an apparent sound change in the way the motor sounded when running when i switched, some may not believe this, but i listen very closely to my motors, very tedious to their working condition, just the way i am. It just seemed to run alittle smoother, quieter.

Still, i won't be switching back to conventional oil anytime soon, and both trucks running Mobile 1 filters.
 
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I switched to Castrol 20w50 last Sunday. The pressure stayed at or above 30 at hot idle until today. I had a longer than normal drive to work because of the weather and it was dropping down to 15 again. I was finally able to find the right oil pressure sending unit and replaced it today after I got home from work but have not drove the truck around since. Just started it to make sure it was working with no leaks. I am going to go back to 10w30 but add Lucas synthetic stabilizer to it this weekend. This was the wrong time use that thick of oil. It is getting down to the single digits here and it does not run worth a damn now. It acts like I'm dragging a overloaded trailer now. Bogged down bad. Next if the new sending unit don't fix it I'm going to get a manual gauge to see if my gauge or wiring is bad.
 
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Update, After I replaced the sending unit I drove for it for a 230 mile trip. The oil pressure stays consistent now but still at hot idle in gear it is dropping to 10psi and in park it is just under 30 psi. Im starting to think that with all the sludge that came out of it that possibly the pickup is getting clogged. After I run it for a while the psi drops but if it sits for 30 min or so and I start it back p the hot idle psi is back up to normal until I drive it around a little. My next step is going to be dropping the pan and replacing the pickup and cleaning out the pan. Also online there is a oil pump kit that comes with a drive gear, gear and shaft assembly, pressure relief valve and pressure relief springs, 3/32 in. x 3/4 in. pin, oil pump drive shaft retainer. Is this something that can be replaced easily and can fix the pump if it has issues?
 
I'd just buy a new oil pump,if your going thru all that work..the housing of the old pump will have some wear too,especially if it had lots of sludge as you said..and new gears wont fully fix that!..it is somewhat normal for oil to lose viscosity as it heats up,and that shows up as pressure drop on the gauge..the 10 psi for every 1000 rpm's is what most engine builders say is the minimum pressure,sounds like your right on the verge..might not hurt to pull off a bearing cap and see if the bearings look scored or worn while your in there...if your bearings were a bit loose or worn,a new oil pump mihght help restore the pressure,but a lot of oil will get flung out of the bearings and could lead to smoking or other troubles..I stay with stock oil pumps too,I have seen "high volume" or high pressure ones give grief rather than improve anything more than once=--often the engine needs other mods to usde one sucessfully..
 
I have dropped a couple of oil pans now due to very dirty engines and clogged pick-up.

One i actually did myself, as i cleaned out the top end to remove the sludge deposits and whatnot, i tried to prevent stuff from dropping to the pan, but failed in that. Was on a '95 Dodge Intrepid, got everything on the front of the engine fixed, which was a real fun job i might add. took it for a drive and all was fine for a bit while going up and down my street, then the oil ilght flickered a couple of times, and a few more passes down my street, it stayed on. I pull it into my garage, hit park, open the hood and it sounded like a Diesel engine. The top end was clattering pretty well.

Ended up dropping the pan and sure enough, more hardened crud was in the pick-up screen. Cleaned out the pan, screen and whatever else i could do while there, sealed it back up and the oil light went off and the motor was as quiet as brand new.

Dads Aveo was a lack of regular oil changes, 130k miles may have seen 4 oil changes, had to replace a transmission, and while running in the driveway, it just didn't sound right to me, again, clattering.

Decided to drop the pan, was pretty easy on this one, and saw all the crap in there, and BARELY any opening on the pick-up screen. I chewed his ass out for lack of maintenence, had to teach him a few things, cleaned out the engine, changed the oil twice within a 1000 mile period, then finalized it with 10/40 synthetic, and top end filter. Motor still going strong, quiet as new and not burning any oil either.

If you're going to drop that pan i would also suggest going ahead and replacing the oil pump, it's one of those "might as well since it's apart" deals i look at when working on cars. If i can afford it really:D

and yeah, 20/50 in cold weather is not friendly to the motor, i found this out one year when i lived in Flagstaff, Arizona. Tried to start the motor when it was like 4* outside, really slow starting and the motor even sounded like it was struggling to stay running. Also needed to add more antifreeze to the mix too i found out one morning when the radiator froze up:doah:





check this out, Fordum is wearing off on me here :doah:
:D
 
I was just looking at the autozone web site and noticed a replacement it fairly inexpensive. I am going to install a new one. What do I need to torque the cap back down to. I have never done any internal work so is there anything I will need to do to make sure it goes back on right and do I need to put anything on the bearing before I put it back on to make sure it wont get messed up when I start it back up?
 
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