Oil pressure gauge reads low and knock on cold start in small block

[crazy4offroad]

The pic with the circle is 89S's pic from his thread.

 

[austinado16]

Well, I decided to quit being a woos, and put a friggin' gauge in it.

Just finished.

Replaced the original brass pipe with an 1/8"NPT 2-1/2" long pipe, into a T that had 1/4" NPT on each side. The original sender went back in on the left, and on the right I put a street elbow and came straight up. The plastic oil pressure line goes from there, up over the cruise control diaphram, into the main harness and under the brake booster, and then into the firewall. Mounted the gauge at the bottom of the dash, just to the left of my trailer brake controller. On the right of that controller is the trans temp gauge.

Looks good, matches the other gauge. Bam, done.

Turns out my factor in-dash gauge is on the money.

Cold start: 30psi
Cold 2000rpm: 36psi

Hot idle in gear: 18psi
Hot 2000rpm: 32psi

Hot 7,200rpm.........just kidding.

Reset the timing to 6BTDC and it's good to go.

I'm going to pull the pan, replace the pump and roll a set of bearings into it. I watched the gauge on cold start and listened to the knock. As either gauge comes to life, the knock immediately stops. Really sounds like the crank knocking.

One thing that's weird about the oil pressure is that it doesn't increase much. Makes me wonder if the pump isn't worn, and/or the bypass valve is leaking pressure at all times. I would think at cold start, it would make 50-70psi rev'd, even if it was just for a few minutes. Instead, it climbs to 38 and just sit there.

I hear ya on the value/rebuild thing. To us, it's worth it. We're not making a payment, or paying for full coverage insurance on a 40k rig, or the crazy CA licensing fees based on value. And even better than all that, we don't look like every socker mom in her Yukon. *puke*

Question: What's normal oil pressure for these SBC's?

 

[bucket]

Question: What's normal oil pressure for these SBC's?

Yours is pretty normal. You just want at least 10 psi per 1000 rpm.

 

[HotRodPC]

The pic with the circle is 89S's pic from his thread.

I'm not thinking that's that bad at all. Unless you're running a high pressure pump you'll never see 50-70 lbs in a SBC. Yours isn't to bad at all, especially for 276K miles.

 

[austinado16]

I'm not thinking that's that bad at all. Unless you're running a high pressure pump you'll never see 50-70 lbs in a SBC. Yours isn't to bad at all, especially for 276K miles.

Oh, okay, thanks! I don't know what's normal for an SBC. Mmm....maybe I don't need to take the pan off.

 

[HotRodPC]

Oh, okay, thanks! I don't know what's normal for an SBC. Mmm....maybe I don't need to take the pan off.

Not unless you're wanting to replace the bearings. My crate 350 that is very low mileage runs about 40psi cold, when warmed up it runs about 30psi at high idle, and about 35 warm going down the freeway. But, we're talking about a new motor too. My tired 350 would get down to 20 ideling and about 30 on the freeway. Trying a bit heavier weight oil and some high mileage formulation may bring it up even a bit more and help some with the knock. For as long as you say you've had this knock, it's obviously not a rod bearing cuz it would have took flight and spun by now. And the knock might even be some piston slap as C4 suggested from a piston rocking in the cylinder, or a loose wrist pin which if it is either of the later suggestions, new bearings won't fix those issues but the likelyhood of the motor coming apart for those issues is slim to none. Just get used to the knock and drive it.

 

[towman]

the knock could also be a cracked flex plate

 

[HotRodPC]

the knock could also be a cracked flex plate

Sure could. Forgot all about the simple suggestion.

I once bought a Camaro for $100 cuz it had a rod knock. I fired it up and KNEW it was the flex plate. Oh yeah, that's a bad motor for sure. Here you go, paid him and drove it home. Put a flexpalte in it, and sold it for $500 a week later.

 

[austinado16]

The reason why I think the knock is crankshaft, is because it responds to the initial hit of oil pressure. Pistons and wrist pins don't get oil pressure. It's not the flex plate because the tranny has been out 3 times in the last 5 or 6 years, and we would have seen that.

I initially thought it was the crank banging back and forth from front to back......end play....but I've tried to pry the crank in both directions with a prybar and it doesn't move.

I'm still considering taking the pan off and doing a new oil pump and bearings, but I'm not as concerned about it now that I know what kind of oil pressure a new crate motor makes.

I'm used to the kind of oil pressure that German cars make, so when I see 30 hot, I think, "Oh ****." My Rabbit diesel pickup produces about 100 cold, and 60+ hot, going down the road. A mechanical gauge actually can't be used in the diesel long term, because they eventually burst! Back in the day, if you didn't use the German oil filters, a fram or other crap-ass filter would get blown off the engine on cold start. Now that's oil pressure!!

 

[HotRodPC]

No, Your oil pressure seems to be normal inline with a 276K mile motor for a SBC. My BBC runs higher. It keeps the needle pegged at 60 at anything above idle hot or cold. It likely has a high volume pump in it though and it's also a low mileage motor.

 

[89Suburban]

Not in the pic with the circle it don't but,

In the pic I did figure out where the Z bolt bosses are, and on this block they are not drilled and tapped. See the flat spot near the O2 sensor? That is where Z bolt boss goes and it's not tapped. The other one goes at the same height very near the back of the block and in this pic, the auto trans bell housing ear covers it up so it's not seen in the pic.

Ahahaha, you should know that is not a pic of C4's motor, it would be caked in mud lol...

 

[HotRodPC]

Ahahaha, you should know that is not a pic of C4's motor, it would be caked in mud lol...

I knew it wasn't his. He assumed I was reffering to his motor when I point out there was NO sender switch in the hole and I was reffering to your motor. The one with the red identity circle on it.

 

[austinado16]

No, Your oil pressure seems to be normal inline with a 276K mile motor for a SBC. My BBC runs higher. It keeps the needle pegged at 60 at anything above idle hot or cold. It likely has a high volume pump in it though and it's also a low mileage motor.

Good info, thanks. Makes me feel better....although I don't know why I'm worried about it now, it's been like this since buying it from the Goodwill Donation Center in 2004. I guess it's because camping season is upon us, and I'm thinking, "Is this the year that we grenade it on some long, hot, steep hill climb in BFE?"

Actually gonna go for a test tow up the local grade and see how the new radiator does, and what the working hot oil pressure is......and also, make sure my 6*BTDC timing doesn't rattle with the 91 Octane corn fuel I'm burning.

 

[HotRodPC]

Good info, thanks. Makes me feel better....although I don't know why I'm worried about it now, it's been like this since buying it from the Goodwill Donation Center in 2004. I guess it's because camping season is upon us, and I'm thinking, "Is this the year that we grenade it on some long, hot, steep hill climb in BFE?"

Actually gonna go for a test tow up the local grade and see how the new radiator does, and what the working hot oil pressure is......and also, make sure my 6*BTDC timing doesn't rattle with the 91 Octane corn fuel I'm burning.

ahh yes. That's all you can get in Cali now is corn fuel blended isn't it? I think you're gonna be just fine. If anything, next oil change go with the higher weight oil and use the High Mileage formulation.

 

[austinado16]

Okay, some test results....

Hooked up the 2,100lb tent trailer, and hauled up over our local 4mi long 6-7% freeway grade. Prior to the climb, I did a little 5mi round trip on the freeway, to get coolant, engine oil, and tranny oil up to temp.

Climbing what we call, "The Grade" I had maybe 24psi, in 3rd, torque converter onlocked, and spinning about 2,600rpm at 50ish mph. Crested the grade and pulled into a parking lot off the freeway. Had about 12psi of hot idle, in gear, oil pressure, and maybe 20-21 in OD with the torque converter locked.....1900rpm.

Drove back into town and visited the NAPA store on the way home. Picked up a new industrial NAPA Gold 1794 oil fllter (these are huge and bring total capacity to 6qts), along with 6qts of Castrol Syntec 10w/40.

I'm always in the mood to learn more about oil, so happy to hear opinions. I'm a fan of synthetic oil (but not a fanatic about it) and not a fan of the additive packages in the high mileage oils. To me, the "High mileage oils" are a marketing scam. But that's just me, and as I said, I'm willing to hear real facts.

Did a hot oil and filter change, and went back up "The Grade." The 10w/40 gives about 4-5 additional psi. Really more like 4. So right now, I think it's a smart choice. I'll be putting it to the test next week when we haul up into the mountains on some seriously long, 25-35mph 2 lane grades. I think the big one east of Fresno, CA is something like 25mi long, and goes from about 200' elevation to 7,500'. It's not all continuous climb, but the final 10mi is.

Next item on the list is new bushings for the front springs. Having a buddy do that on Wed. because I simply don't feel like learning it.....or doing it.