That's what happened to my sbc. One of the symptoms before knocking like a SOB was no oil pressure at idle. Sometimes it had it, then none all together.
The old rule of thumb for sbc oil pressure was 10 psi per 1000 rpm. Your idle speed is likely under 1000, so 6-8 psi would probably be acceptable as long as the pressure is coming up with the rpm. Bob
I agree. I'd surely put an idiot light on it, change to 40-weight and listen for ominous noises. Chances it'll run a long time by keeping the oil in it and not beating the **** out of it. Maybe turn up the idle a tad. Bob
I know all of you will think I'm nuts, but I had a 350 in an OT 73' Datsun pickup and had started to have the same issues. Just started to run heavier oils in it as the pressure was slowly going away, started with straight 40 wt. When I finally sold the truck about 2 yrs. later I was running three qts. 50 wt and 2 qts 60 wt motorcycle oil. Every time I would raise the oil wt. at oil change it would get a little oil pressure back. I ran the piss out of that little truck on a daily basis, never a knock or any problems. Best I can say is it was just slowly wearing out. It had 160,000 miles on it when I put it in that truck. I even drove it to the ranch I used to hunt at an hour and a half each way a time or two.
I used to do that with my s**** metal haulers in the '70s. 40 wt... then 50 wt and I'd call it quits with Valvoline 60 wt blower oil. Tossed in some supplements like STP and that Alemite CD2 if it was an oil burner as well. Bob
Pop the pan, check bearings, you need to look at the upper halves as thats where the rod bearings get hammered, pop out a main bearing and look at those. I had the same symptoms on my Pontiac 400 . I checked the bearings and they looked like new even after many 12 second blasts down the 1/4 mile and 15 years of reving the **** out of it on the street. This was with 10.5 :1 compression. Well I took the pump off and there was grit between the pressure relief ball and seat and the teeth and face of the gears were scored a bit. I replaced the pump and I was rewarded with 25 psi at idle and 60 psi at cruise. No damage to the engine. Oh and cold I had 40 and warm 0. Before replacing the pump. This wasn't gradual , it dropped suddenly.
GM specs call for 40lbs of oil pressure @2000 RPM. The warning lights don't come on till 3lbs. The idle number is way to low for me as I'm sure is for you. I've read on other threads in here about having low oil pressure when using a Fram filter. Really don't believe that's the problem,would be a kick in the *** if it was though !!! Might be worth a try especially if your running a Fram !!!
You need to check clearances on the mains and rods, how much side clearance on the rods and something often overlooked, the cam bearings.
As much as no one wants to hear that a rebuild is in order, my guess is that is exactly what you are looking at! However, the suggestions that you switch to a straight viscosity oil rather than the multi-grade you have been using could gain you some extra time on the engine without the fear of the no oil pressure at idle you have been dealing with. I know this for a fact as I have been dealing with the same scenario on my 389" Pontiac in my '63 Bonneville. If I use milti-grade oil, the pressure will drop to zero after the engine has been running for a while. At speed, the oil pressure is good. By merely switching to a straight 40 wt. oil, the pressure never goes much below 8-10 pounds at idle. While this is only a band-aid for your problem, it will give you some time to get your ducks in a row to deal with the rebuild you are definitely facing. Good luck...
Sounds like bearings a little loose to me. If you want to fix it, your probably gonna have to pull the engine down and replace them (main/rod/cam bearings). If you just want to patch it up until later a high volume oil pump will make you feel better when you look at the gauge. I might try a straigt weight oil too. I'm really clueless when it comes to oil, but I've read that multi weight oils are really the bottom number viscosity with additives to make the oil flow slower (not thicken) when the oil gets hotter.
A small block with 10 psi at idle and 40 psi running down the road will last even if you beat on it to 5000 rpm.If the oil pressure jumps up to at least 30 psi at 1500 and 40 at maybe 2500 rpm ,you're good to go.If it runs ok,doesn't smoke,use 20/50 oil and turn up the idle until you see 10 psi.Of course if the pressure continues to drop there is a serious problem.
If it was not a SBC or a Flathead Ford I would say you have a serious problem but both of those motors can go a lot of miles dispite having little or no oil pressure at idle! As long as you have decent (35-40) oil pressure at driving speeds don't worry drive it like you stole it until it blows up then rebuild or replace it. Taking the oil pan off "just to have a look" will likely do nothing except get oil in your eye.
I'm with truckedup. Low oil pressure at idle is common SBC complaint. Oil flow is way more important then pressure anyway. There's been numerous posts on this subject on this and numerous other sites. As long as you meet the 10# of pressure per 1000 RPM I'd drive the wheels off it. So have numerous others. Putting in high viscosity oil is no fix. Save your time and money and leave it alone. If you want oil pressure stretch the pump spring (just kidding). When I was young and dumb I stretched it so much that my oil pressure gauge would peg on hard acceleration. Adjusting the solid lifters made a mess. Back in the day, a friend of mine had a 55 Ford Mainline line with a worn out 390 Cadillacin it that had little or no oil pressure. He drained the oil and filled the crankcase with Motor Medic to raise the pressure so he could sell it. What a Douche.
Messing with the byp*** isn't gonna help low pressure at idle. Without looking at the engine, the problem can't really be diagnosed. But I'm guessing the OP is gonna have to move more oil or tighten up the clearances to get more pressure at idle.
Famous last word, "lemee take the pan off to check my bearings", which also reeks of a on-your-back bearing change job. I've had countless 283 Chevys that I ran for years on sheer neglect. Once you open one up, be prepared to **** or fall back. Bob
Plugs meaning the oil galley plugs. They are like real small cups, like mini freeze plugs. When the block is originally machined, the p***ge needs a path for the machining, but once built, the hole needs to be blocked off. You could put a new oil pump, cheap enough, just the labor to pull the pan to get to the pump. A new byp*** would be easy to install and check, it is right inside above your oil filter. I am with the rest that your engine just has some excess clearance and that is why the low pressure at hot idle. Unless the engine is something extra special, I would just run 20w50 oil and let it be. At idle it does not have any real load on the engine. Zero or a few psi pressure does not mean no oil flow. Pressure is resistance to flow. Since pressure comes up when you increase rpms, all your oil system is working. Just the clearances are enough that at hot idle, it all flows out and no resistance.
The byp*** that sets the oil pressure is in the oil pump. The filter byp*** could possibly cause problems, but it's not as likely as the pump by p***. It should be closed at idle unless the spring is broken or the by p*** valve is stuck open. But the oil pressure wouldn't come up with the RPMs, if that were the case.
Right, I was thinking the filter byp***. Correct the oil pump byp*** is in the oil pump housing. Fingers typing faster than my brain...........
ok so I pulled the pan, I didn't see anything clogged in the screen, I am seeing a little sludge at the bottom of the pan by the drain plug but not much. I am also seeing what appears to be some br*** shavings at the bottom as well. this concerns me. (should it)? I think I am going to change the oil pump make sure the pick up tube is on tight put some 40 wheight in it and see what it does. Should I do something different or something else?
you have the pan off you can slip a set of bearings in easy, at least pull some bearing caps off and see how they look, use some plastic gage.
If you have br*** shavings they came from someplace? Most likely some of the bearings are worn down to the br*** or copper.Since you have already opened this can of worms Inspect and if they are worn replace the bearings.
Had a new motor lose idle oil pressure after only 2000 miles. Pressure relief valve in brand new oil pump was sticking.Im damn happy I tore the whole thing down to find it....live and learn.
Old Wolf is right. Br*** shaving in the oil is a sure sign that your bearings are worn somewhere in your engine. Popping a rod cap is no big deal. You should be able to see if the babbit is worn off the bearing. Also if this is really a rebuilt with low miles, I'd be a little su****ious of sludge in the pan. Whatever happens don't feel that you are alone. We've all had our share of "rebuilds" that ended up bad, broken or a boat anchor.
Do not use 40wt. This is too thick and takes too long to circulate when cold. This is a sure way to kill your engine sooner than later. Use 10-30 when you find the problem. Make sure you check the tops of the rod bearings as this is where detonation will hammer them.
I had this same problem with a 400 pontiac years ago. The stock oil pump had a sheet metal cover (10 gauge maybe?) The cover had distorted between the 4 bolts and was leaking volume and pressure between the cover and the housing. Changed it to a high volume pump with a cast cover that was approx. 1/4" thick, which cured the low oil pressure at idle. Before the fix, the oil pressure gauge fluctuated up and down almost in sync with the tach. I always look at the oil pump I'm going to run for this problem.
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