Low / No oil pressure question sbc 350 - Team Camaro Tech
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post #1 of 20 (permalink) Old Mar 30th, 09, 04:02 PM Thread Starter
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Derek
 
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Low / No oil pressure question sbc 350

I have a question in reference to the oil pressure on a small block 350. The motor is currently in a 67 camaro and has approximately 300 miles on it since a rebuild of the short block. When I first start this vehicle, the oil pressure is great (around 40-50 psi), but as the engine temperature increases, the oil pressure drops. After the motor is completely warmed up (around 190-200 degrees) the oil pressure gets very low (at 0 / almost 0).

Yesterday, I started the car up to let it warm up. After it was warm, I drove it down the road approximately 3-4 miles (got on it a little bit.) While I was driving the vehicle, the oil pressure was fine, but as I came to a stop (at idle) I looked down and the oil pressure was 0. The car immediately died. The car was then very hard to restart. This has happened before and I would like some imput on what could possibly be going on. What could be some reasons my oil pressure is dropping to 0 after the car is warmed up and driven kinda hard?

I am using a mechanical oil pressure (autometer) guage that is connected to the rear of the intake manifold.

The short block is rebuilt, the the heads on the motor are older, and possibly need rebuilt. Is there any way that worn valve guides would cause this? or do I definately have a problem with the oil pump, bearing clearances, etc? Thank you for any imput, Derek

Last edited by pro67street; Mar 30th, 09 at 04:12 PM.
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post #2 of 20 (permalink) Old Mar 30th, 09, 04:15 PM
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Re: Low / No oil pressure question sbc 350

Verify your gauge is correct. Has main bearing failure written all over it IMO
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post #3 of 20 (permalink) Old Mar 30th, 09, 04:26 PM Thread Starter
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Re: Low / No oil pressure question sbc 350

I have used two different autometer mechanical gauges and both showed the same results. I am positive its not the gauge, unless I have it hooked up wrong. Its hooked up to the back of the intake. It has one of those "see through" tubes that connects from the rear of the intake to the rear of the mechanical gauge. When I am driving, or when I am giving the motor gas, I can see oil flowing through the tubing. But when the car gets hot and is at idle, the oil flow completely stops.
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post #4 of 20 (permalink) Old Mar 30th, 09, 04:28 PM
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Re: Low / No oil pressure question sbc 350

It's not really the intake it's right behind it. Have you changed the oil and filter? If you have then it's time to pull the engine and figure out what went wrong.
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post #5 of 20 (permalink) Old Mar 30th, 09, 04:31 PM Thread Starter
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Re: Low / No oil pressure question sbc 350

Yeh, im sorry, the hole is right behind the intake...yeh, ive changed the oil...same results. Im sure it doesnt matter, but would the viscosity of the oil I am using have anything to do with it?
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post #6 of 20 (permalink) Old Mar 30th, 09, 04:48 PM
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Re: Low / No oil pressure question sbc 350

Quote:
Originally Posted by pro67street View Post
Yeh, im sorry, the hole is right behind the intake...yeh, ive changed the oil...same results. Im sure it doesnt matter, but would the viscosity of the oil I am using have anything to do with it?
possibly.....what oil grade are you using? My built 406 has about 60-70 lbs when cold at idle. As it warms up, it drops steadily to 40 or so. When I drive it for a while, and the t-stat opens at 180*, the oil pressure is around 40-45 psi, and when it returns to idle, it has about 8 psi. I questioned my engine builder on this and he said it was normal, and that I didn't need a lot of oil pressure when the motor was idling. However, you have none.....I would try using a straight 30 weight oil first with a purolator pure one filter to see if it helps. If it doesn't, then there is something up with the bearings as previously suggested.

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post #7 of 20 (permalink) Old Mar 30th, 09, 04:55 PM
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Re: Low / No oil pressure question sbc 350

First off, what you think is great oil pressure (40-50 psi) when initially started ain't so great!.....The engine oil pressure should be between 65-75 psi when initially started (cold)!.....When the engine is up to operating temperature (hot) it is normal to drop to 35-40 psi but never any lower!.....These oil pressures are based on using a straight 30 weight motor oil.....I doubt using a thicker viscosity oil will increase the oil pressure if it's already dropping to 0!.....Are you sure you're not hearing any knocking noises or a dull thud noise coming from the lower end of the motor as it appears to be worn main bearings to me!
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post #8 of 20 (permalink) Old Mar 30th, 09, 05:11 PM
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Re: Low / No oil pressure question sbc 350

For a stock pump it would be alright. My big block has 45-50 cold and 20-25 hot at idle with a stock pump. Cold oil pressure means very little. That hot at idle is when you find out how much bearing clearance you have.
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post #9 of 20 (permalink) Old Mar 30th, 09, 05:59 PM Thread Starter
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Re: Low / No oil pressure question sbc 350

the motor has a noisy gear drive in it so i cant really hear anything besides that..although i do hear a loud ticking noise when i rev the motor up, but i just thought it was valve noise? i currently have 20-50 weight oil in it.
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post #10 of 20 (permalink) Old Mar 30th, 09, 06:43 PM
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Re: Low / No oil pressure question sbc 350

I would have to agree with Todd:
symptoms of bearing failure.
worn valve guides wouldn't affect the oil pressure in that manner; you'd see lots of blow-by or blue~ish exhaust smoke.
being hard to start after a run indicates (to me) rod and or main bearings seizing.

can you give some detail about the recent rebuild, the start-up process,, and which 20-50 oil ?

I've sat in your same chair man.. helped a buddy install a "fresh" 350 which he replaced bearings in, 1 yr ago this month. He failed to gauge everything, and because the rods were .020, he assumed the mains were too.. wrong.
it ran 20 minutes before doing exactly what you're describing.

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post #11 of 20 (permalink) Old Mar 30th, 09, 09:15 PM Thread Starter
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Re: Low / No oil pressure question sbc 350

Well, I guess its gotta be something with the bearings then...I bought this motor from a kid for like 150.00. the kid claimed it was rebuilt and yada yada yada...so i take it home and pull the oil pan...5 out of 8 rods / pistons were backwards...lol. so i pulled them out and turned them all around, I checked all the bearings which appeared to be new, then retorqed everything to specs. I didn't check any bearing clearances or anything like that. I just kinda threw it together hoping it would run. No big deal tho...so????, pretty sure its the bearings / pull the motor? Anything else I could try before doing that? Any tests I could do?
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post #12 of 20 (permalink) Old Mar 30th, 09, 09:24 PM
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Re: Low / No oil pressure question sbc 350

No.....you could put a brick on the pedal and see how long she'll go. LOL If you want to save it....tear it down.
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post #13 of 20 (permalink) Old Apr 1st, 09, 09:02 PM
Josh
 
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Re: Low / No oil pressure question sbc 350

I ran into this after replacing crank bearings, the cam and the oil pump on my 350. It did the same thing as you're describing. I thought the only problem could be the oil pump was defective from Summit. It was a high flow melling(I think). I called Summit and had them send me a new one with a new pickup. I changed it out and it still had the same symptoms. So I started searching the net...

I found that FRAM was the culpret. I changed the brand new FRAM filter to an AC Delco oil filter and the pressure was fine.

I read a bunch about how some filters are cardboard inside and some are made with better insides. If I were you, I'd try this $5 fix before pulling the engine/pan.

Hope this works for you,
Josh

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post #14 of 20 (permalink) Old Apr 2nd, 09, 01:50 PM
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Re: Low / No oil pressure question sbc 350

Derek. Look at the bright side. You'll never make this mistake again! Good luck with the oil filter fix. Yeah, I think Fram is junk but that's a real long shot.

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post #15 of 20 (permalink) Old Apr 2nd, 09, 02:16 PM Thread Starter
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Re: Low / No oil pressure question sbc 350

haha, yeh...ive made plenty of mistakes so far when it comes to cars...I'll keep learning I guess. I will try the AC Delco filter and let you know what happens...you're right "long shot" though.
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