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Oil pressure question

Orange85

Orange85

1/2 ton status
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May 10, 2009
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Location
Wisconsin
Story:

I have a 327 in my truck that has been a really good motor up until recently. I noticed a few weeks ago that the oil pressure isn't where it should be, so I haven't been driving it or starting it. Now today I started it up (I start all my vehicles every couple weeks and let them run and get hot so moisture can go away) and I have 15 pounds at cold idle (30* outside) so I knew there was something wrong. But all of a sudden it just dropped to zero, I heard some noise and shut it down not even seconds after I heard it. Then the pressure came back when I started it again. (No noise)

I have worked this motor hard so I am suspecting something is wrong and not something that is a fluke.

Question:
What would cause the pressure to drop and come back and just drop off again repeatedly? It does this if I leave it running also. I was thinking bearings but I thought that if it was a bearing the pressure would stay gone.

I also changed the oil filter thinking maybe something was an issue there but no difference other than the pressure went up to 20 pounds and then promptly dropped to 0.


Any suggestions would be greatly appreciated. If it is bearings I am just gonna build the 4 bolt 350 I have access to.

Thanks,
Shawn
 
I am curious what kind of noise you heard when the pressure dropped to nil.

I would verify the oil pressure by putting a new mechanical guage on the engine before you assume too much. The quick dropping and returning pressure is not a common problem when a engine is failing in my experience.
 
Sounded like a lower engine noise. Verified no oil pressure when I pulled the valve cover and had no oil coming up top. To me it sounded like a rod bearing went bad but only for a second. When I started it up again there was no noise and when the pressure dropped again there was no noise. It wasn't valvetrain noise.
 
Well, I guess it does sound like a rod or main bearing has failed and the pressure drop comes from when it spins out of position and dumps the oil or blocks the oil galley and thats when you get the low pressure reading.

Pull it out and build up a new one.
 
Thats the plan I think, got an engine to swap in for the winter I think. Buddy has a parts truck that I can get the engine for cheap from... So Build up over winter to have ready for next mudding season...
 
It could be the pressure relief valve in the oil pump giving you issues. If it were a bad bearing the pressure would not come back. The oil pump is designed to give a certain amount of oil pressure before the bypass spring is overcome (fail safe so you don't have too high of oil pressure) but the clearance between the cam and cam bearings, crank and rod/main bearings is what will dictate how much oil pressure the engine will make (the tighter the clearances the more oil pressure you'll have and the looser the clearance the lower the pressure will be).
 
I suppose it could be the loose oil pickup tube working its way up and getting smacked back down by a rod cap.......
If your truck is such that the pan can be dropped without a lot of trouble, might be worth while to check the pump.
 
I've seen a few small blocks do the same thing--and it was the oil pump's driveshaft ,that has a nylon "collar" that joins the driveshaft to the oil pump shaft,that had broken and it allowed the shaft to slip in and out of alignment with the oil pump shaft ,and cause it to stop pumping!..they sell a heavy duty steel collar to replace the crappy nylon one ,Sealed Power,Melling,etc have them listed and they only cost 5 bucks or so...

Of course if the engine was starved for oil long enough,you might now have some bearing or lifter troubles--be best to take a main and rod cap off while the pan is off and inspect them for wear or any sigh of having "spun"....might as well replace the oil pump and the driveshaft collar while your in there--last one I bought was a stock replacement for a 305 at Autozone,it was only 12.99 for the pump,about 10 more for the steel collar and a new driveshaft for the pump..
 
Well today I had some free time after work so I pulled the pan and put in a new High Pressure High Volume pump and cleaned the pan.

When i dropped it, I saw what looked like mud on the bottom of the pan. Also it smelled like gear oil for some reason. And no I did NOT put gear oil in it. I put lucas in at the last oil change but I have never smelled it. Does that smell like gear oil?

The pick up tube and screen was bent upward but I didn't pay attention to see if it would have been above where the oil level would be or not.

Anyway I put regular 5W30 semi synthetic in to clean it out for about 15 mins and then changed the oil again.

Now I have about 75-80 psi at cold idle and about 60-65 at warm idle. It rises and falls with rpm's like it should. Also no engine noises that I can hear. So I hope this will hold it over for awhile.

Edit: Also I had the steel collar with a roll pin in it for the oil pump drive shaft so I saw no need to change it.
 
Lucas does have a slight odor something like gear oil--but so does some newer motor oils,I've noticed that myself when I watch my friend drain oil from customers vehicles doing oil changes..maybe synthetics stink like that sulpher smell gear oil has?...I know used Quaker state stinks more than most other brands,I've seen it gell up like jelly more than once too!..
 
Ill have to pay attention next time I have some lucas in my hand. I used Castrol 10W40 the last time cause it was getting colder and that stuff didnt even pour out when cold, it came out of the oil pan like molasses lol
 
I used to use Castrol 20W-50 in my older V8's years ago,that stuff wouldn't even pour out of the bottle if it was below 20 degrees,looked like maple syrup!..the engines always started with it though,but sounded like nothing got lubed for the first few minutes..I liked it because it seemed to not burn as much or leak as fast as thinner oil,and it kept my oil pressure higher in hot weather...
 
I can't remember where i either read it, or heard someone tell me, the reason the manufacturers are going with thinner oils now, is because the oil technology is much better these days, much better lubricant, and the thinner oil gets to lubing much faster during those start-ups, it moves easier and gets to where it needs to be real quick.

I did have some 20/50 in a high mileage motor several years back in the Burb, then relocated to Flagstaff, Arizona shortly before winter hit, i went out one morning to start it when it was like 4*, and it had a hard time starting, cranked real slow, once it did get started it just sounded like it was struggling, not missing, just lugging, like it was under strain.

I swapped out that oil the next day for some 10/40 and it was much better.

I would always run the 20/50 because i lived in Phoenix, so seeing those extreme hot days, it always seemed to work good especially with all the highway driving i did.

I'm currently running a 10/30 full synthetic and it starts and sounds just fine, just went somewhere alittle while ago and it was 17 degrees out.

Now i need to work on the cooling system, stupid thing won't warm up completely :doah:
 
That is one of the advantages to synthetic.
I saw a demo where standard 10W30 oil would barely pour out the bottle at some low temp, and the same in synthetic poured out like it was summer.
 
Fordum said:
That is one of the advantages to synthetic.
I saw a demo where standard 10W30 oil would barely pour out the bottle at some low temp, and the same in synthetic poured out like it was summer.
Click to expand...
well even the conventional 10/30 is going to pour out better than 20/50. it is a much thinner oil, i couldn't use it in that higher mileage motor, cause the valve seals were toast and i would go through a couple of quarts between oil changes.
 
I switched from the Castrol 20W-50 to Castrol 10W40 for winter but we will see how this goes with the 5W-30 in there for now.
 
I liked to use 20W-50 or SAE 30 or 40 oil in warm weather in my old trucks with high mileage,especially if they used a bit of oil between changes....some cars I had were so worn out the engines consumed a quart every 250-500 miles,but by using 20W-50 or the straight weight oils,along with a additive like Lucas or STP,Motor Medic,etc,I could go close to 1000 miles before I had to add a quart..those engines were "loose" too,without the thicker oil I'd get lifter clatter and piston slap,and if I tried using a thin oil like 10W-30 the oil pressure would drop quite a bit...

I have read in many articles on oil that thin oil DOES lubricate more thouroughly than thicker oil,even in my aincient Audels motor manual "bible" from 1941 stated exactly that--they only had straight weight oils then,SAE 10 was the thinnest and Dodge reccomended it over all other weights ,excepting hot weather high speed driving when they reccomended SAE 30 or 40W oil...

I suppose with todays higher precision ,engines are built "tighter" than ever before,and only thin oil will penatrate the close tolerances and lubricate properly...cant say I've seen any engines that starved for oil due to someone using thicker oil though,but in cold weather you definately can hear the difference if you run thick oil VS thin in the first few minutes after a cold start..

I prefered to use the thicker oils and let my engines warm up a few moments before driving in cold weather,because the engines with lots of wear needed the thicker oil film to maintain oil pressure when hot..the Audel manual stated "For low speed high load use a thick rich bodied lubricant is prefered,but for high speed low loads a thinner lubricant provides better lurication"....todays synthetics are great for cold weather as they dont gel up like regular petroleum oil will,but I hesitate to use any in an engine thats real high mileage that had never seen synthetic before,it might be "slippery-er" but I dont feel it has sufficient viscosity to keep loose bearings quiet and keep oil pressure up where it belongs...cant justify the expense either,really..
 
diesel4me said:
,but I hesitate to use any in an engine thats real high mileage that had never seen synthetic before,it might be "slippery-er" but I dont feel it has sufficient viscosity to keep loose bearings quiet and keep oil pressure up where it belongs...cant justify the expense either,really..
Click to expand...

i just switched two vehicles here in the family over to full synthetic, one car has over 140k miles, and the truck with the 4.3 has 230k miles. So far no problems, they both sound better running, not burning any oil, no leaks.
I had a difficult time with the price difference as well, but the way you need to look at it, being twice as expensive, you don't need to change it out for twice the interval, maybe a hair more, so it realy works out to be about the same price, except your getting better lubrication and a more stable, non sludging oil.

Maybe change out the filter still every 3000 like i just did on the car, but the car we just changed a few weeks ago went about 7000 miles and was just barely lookin to need to be changed, i was suprised.
The pick up is running on about 4500 right now, still lookin good and running and sounding fine.

I'm pretty much sold on the product :D
 
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