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Actually I've had an engine that had low oil pressure; about 2 lbs at idle and maybe 8 pounds at 2k if we were lucky. It was caused by a lifter that had a bad piston/plunger.
did the pressure resolve it self as the engine warmed up? As I got to thinking about the time frame and considered this as an explanation for low pressure at startup only.
No, it would get worse. As the oil warmed, the pressure dropped until there was virtually no pressure. I changed the pressure relief valve and spring, oil pump, rod and main bearings, oil grade, you name it. Finally I checked the lifter and one was bad. I couldn't believe it.
No, it would get worse. As the oil warmed, the pressure dropped until there was virtually no pressure. I changed the pressure relief valve and spring, oil pump, rod and main bearings, oil grade, you name it. Finally I checked the lifter and one was bad. I couldn't believe it.
is there any way to identify a lifter not building pressure without removing the intake?
Hard to say. In this case...and if I had known what I was looking for, I may have gotten a clue by the fact that there was little to no oil coming from that pushrod. But with <8 lbs of oil pressure, there wasn't a lot coming from any of the pushrods and it was variable. Realistically, probably not. You could try to use a scope and other tricks, but for a real confirmation....I think you'd need to pull the intake.
Hard to say. In this case...and if I had known what I was looking for, I may have gotten a clue by the fact that there was little to no oil coming from that pushrod. But with <8 lbs of oil pressure, there wasn't a lot coming from any of the pushrods and it was variable. Realistically, probably not. You could try to use a scope and other tricks, but for a real confirmation....I think you'd need to pull the intake.
Don't believe it. Here's why: The orifice that allows oil into the lifter body is about .040. You could remove all the guts out of the lifter body and the "leak" would be the equivalent of that .040 hole. No way can enough oil get through that orifice to affect oil pressure whatsoever. Now if the lifter comes completely out of the bore, then the gallery is wide-open and THAT will affect oil pressure. But not a single lifter. No way.
Sorry, but a single lifter did it. AMC 304. 2 psi at idle....change the lifters (and cam while in there) and had 30-40 PSI at idle.
I agree with your recommendation to check the pan, BTW.
So I think I found the cause of my noise and oil pressure issue. Now the bigger question is why? What on earth would cause oil to go from a dark amber to this in under 500 miles? I used Mobil 1 full synthetic 5W-30 on my last change.
The next question is how do you clean this out once I figure out the cause?
Last edited by Space387; Jul 19, 2018 at 12:14 PM.
Slow leak with nothing on the ground. Did a compression test on the heads and a leak down of the coolant system about a month ago, the cranking pressure was from 185 to 195psi and the coolant leaked out at about 1psi per hr with nothing dripping. I figured that could have been from the seal on the test device as we had to use the adapter cone.
I pulled the intake to look and I'm not sure I see a leak here or not.
I am getting the feeling I still need to pull the heads
* Did forget to mention the 4 inboard bolts for teh 4 coolant ports where hand tight. Not backed out just had very little tension on them to break free.
Last edited by Space387; Jul 19, 2018 at 03:27 PM.
Slow leak with nothing on the ground. the coolant leaked out at about 1psi per hr with nothing dripping.
* Did forget to mention the 4 inboard bolts for the 4 coolant ports where hand tight. Not backed out just had very little tension on them to break free.
...Plus the way that oil looks....is some evidence. That's a tough one. If the intake was still on, you could pressure test the cooling system again and use a mechanic's stethoscope to listen for air leaks around the valley and in the oil returns in the heads.
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Last edited by Tom400CFI; Jul 19, 2018 at 05:17 PM.
With me being so far in, I am probably just going to bite the bullet and do head gaskets too. I'm going to check the heads for warpage and if its within the .004" I think is the acceptable, its just getting gaskets for now. Its getting a rebuild with more gofast parts in the nearish future ( next year or two) but I cant afford that right now and I do want to learn this car a bit better before I make large changes. So time for gaskets, any recommendations?
So I have been doing a bit of reading of ways to ensure it is my heads before pulling them and thought maybe I should do a leakdown test. Would this be worth my time to rule out the head gasket?
I almost suggested that above, but I didn't. Why? The leak down test only tests the integrity of the cylinder or combustion chamber seal. If you had a good seal there, your test results would appear to be "OK", but you could still have a "blown head gasket" that leaks from a water passage to oil. You'd never know. OR you could test and have a leak from combustion chamber to cooling, pull the head b/c you "found the problem".....but there may have been no coolant > oil leak; only combustion to coolant.
It's not a conclusive test. A cooling system pressure test would be better (which you can't do now)....or send some of your oil off for an oil analysis. Then you'll know for sure if you've got coolant in your oil or not.
I have not a clue as to how a AMC 304 oils its lifters. That's sneaky, and experience with a 304 is not related to a SBC.
It most certainly IS related. No sneaky here. Stand by your statement all you want, but I think you're way off the mark. Admit it; nearly all domestic, flat tappet, V8 lifters are pretty darn similar. except for OD and length....and AMC is no different. The oiling on an AMC is just like a SBC as far as lifters are concerned and they oil the rockers the same too.
W/o looking at the pic title, can you tell me if this is an AMC lifter? Or a SBC lifter?
How about this lifter; AMC or SBC?
This one?
1. AMC
2. AMC
3. SBC
Look at the oiling holes; I think we're pretty safe in agreeing that they're all about the same size hole. Let's also remind ourselves where the limit to oil flow in a lifter really is: the orifice in the pushrod cup....not the side of the body.
When a guy told me that a lifter (in a domestic Hyd flat tappet V8) could cause low oil pressure.....JUST LIKE YOU, I thought the idea (and the guy) was completely FOS. It wasn't/he wasn't. A hydraulic lifter in a SBC, SBF, AMC, Poncho, Olds, whatever...if that internal piston goes to ****....that som-b is going to bleed a LOT of oil, fast. That's gonna kill your oil pressure. Keep telling me I'm wrong, but I was a disbeliever too but then I saw it happen and fixed it....first hand.
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Last edited by Tom400CFI; Jul 20, 2018 at 12:12 AM.
Can the oiling passages in the two blocks be different, so the lifter malfunction could affect pressure in the 304, but not in the SBC?
15+ years back, I had a push rod bend and the lifter come out of the bore in the 327 in my ski-boat. It was #2 cyl, so the "leak" was at the front of the engine, after the other 7 lifters on that side. I don't recall what the oil pressure reading was, I presume it was lower, but not alarmingly low because we ran it back to camp, about 4-5 minutes. We replaced the lifter and finished the two day trip. Yes, the cam did go flat on that lobe because we all know we can't put a new lifter on a used lobe. I later replaced the cam, but never touched the bottom end. The engine still runs fine with normal oil pressure, I skied behind it last week.
I can't reconcile how your pressure was so adversely affected in the 304, where mine was not in my 327 SBC by the same general "lifter failure". I'll agree that there must be more that we don't understand, and leave it at that.
EDIT/ADD: I thought of something: Where is the oil pressure sender take-off on the 304? If the reading is taken AFTER the affected lifter, is it possible that the pressure may have been "normal" prior to that lifter, but lower after it? In the SBC, the gauge reading is taken off the main bearing lube journal at the rear of the block. The two lifter oil bores are fed off the rear cam bearing individually. My 327 has a big-azz pump that pegs the gauge at 80psi until the oil warms up, then it runs 60psi at cruise, idle at 45psi. The loss of a lifter at the front of one lifter bank didn't affect the reading at the rear of the block, but if the gauge had been after this lifter, it would have. Cheers.
1. I mean, the whole oiling system appears to be darn similar between the two; the AMC has oil galleys for the lifters just like the SBC and the ID of that galley seems to be about the same.
2. your 327....Cool story, and killer save on the lake! I dig it! What kind of ski boat had a 327 in it? I can't see how your oil pressure wasn't super low; the "waist" of the lifter allows oil to flow around it to move on to the next lifter...even though yours was all the way at the front, it's still a big leak in the system. Not that I think it couldn't run on very low pressure just fine; we know that oil pressure isn't what protects the bearings, it's hydrodynamic lube, so just having any oil there would likely be good enough. Finally, we've seen how long a SBC (Gen III) can apparently go w/NO OIL.
3. Good question about the oil pressure sending unit location. It pretty much has to be between the oil filter and the "engine". On the AMC, it's just inside the front of the block; right after the filter, before the lifter galleys.
I found this interesting page that has "V8 CUTAWAYS". First is a SBC, second is an AMC. You can see the oil galleys in both. Also, scroll to the bottom and check out Pontiac's early reverse flow cooling!
It's interesting to talk about. If I had a ****-box engine to screw around with, I'd pull a lifter apart, fire it up and see what happens.
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Last edited by Tom400CFI; Jul 20, 2018 at 07:55 PM.
So I think I found the cause of my noise and oil pressure issue. Now the bigger question is why? What on earth would cause oil to go from a dark amber to this in under 500 miles?
Seen it happen. I get one or two every 6 mos or so (particularly older Dodge trucks) and the complaint is a crazy shift schedule and no power.
Which makes sense.. They're so hard on the throttle, the schedule can't be normal and it is obviously an engine performance issue. You pull the oil dipstick and it's nothing but sludge.
Frequently, the owner says that's impossible. "I change my oil blah, blah.. blah" Whatever.
Drop the exh and it runs fine. Swap the cat and it is FINE.
That's an interesting one. I've had two clogged cat cars...neither had any noteworthy issues w/the oil or oil pressure. The DID have absolutely zero *****....and wicked "induction noise" when you'd open the throttle.
