Hello, Seems I have a problem here. I have a '68 that I recently pulled the stock 327 out of for a rebuild and put a wild 400 in for the time being. The new engine is suppose to only have around 1,000 miles on it. We took it for a couple of test runs after getting everything together and noticed the oil pressure gauge doing some crazy things. When I accelerate to highway speed the pressure climbs to about 75psi, but then when I let off the gas or slow the car down the pressure drops way off to where it reads right above zero on the gauge. Very nerve racking!! I first hoped that it was the gauge, so I bought a $10 one at the parts store to test it and the same thing happened. My question is, where do I go from here. Do I pull the pan and see if its the oil pump, and how do I test the existing one. Or do I have bigger problems?? I appreciate any help. Thanks......Craig

First a $10 gauge was a waste of $10. Make sure the engine it completly up to operating temp before doing any testing. What is the pressure reading at idle when warm? When you take your foot out of it does iit come back up after a second or two?

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...Dennis
The '69 (http://chevelles.com/showroom/fine69_03.jpg) & the '96 (http://chevelles.com/showroom/fine69_02.jpg)
Team Camaro (http://www.camaros.net)
Camaros Limited (http://www.camaroslimited.com)

That's very unusual. At first, I thought it might be the relief valve spring inside the oil pump, but I don't think it would be able to make 75 psi. And I would think that if there were a bad main or cam bearing (excessive clearances), you still would have a hard time building up 75 psi. The only thing I can come up with at the moment is a small crack in the pickup tube. It's small enough to allow good oil flow when the engine RPM is high, but it allows air to be drawn into the oil system when the engine RPM backs down.

pick up might have fallen off the pump too. That would cause the good pressure under acceleration and the loss of oil pressure under deceleration.

I made sure that the engine was at operating temp and checked the pressure at idle this time. The gauge showed 35psi. I took it down the street this time and when I pulled up to a red light the pressure would drop to almost zero then, when I was stopped it would come back up to idle pressure. The same happened when I came off the freeway. But it doesn't come back up until I get on the throttle again or the car has finished slowing down. So here's a breakdown of what the gauge is telling me. If I'm off the gas and on the brakes or at freeway speeds and let off the gas and let the gears slow me down it drops way down to right above the zero mark. When the car is at idle and in gear it is around 35psi/not in gear its close to 45. If I get on the throttle it climbs to almost 75psi. Well thanks for responding and any help you can provide.
Craig
<BLOCKQUOTE>quote:</font><HR>Originally posted by DjD:
First a $10 gauge was a waste of $10. Make sure the engine it completly up to operating temp before doing any testing. What is the pressure reading at idle when warm? When you take your foot out of it does iit come back up after a second or two?

<HR></BLOCKQUOTE>

Just a shot but could you be low on oil or pumping it all to the top of the block (as suggested already) and when the nose of the car goes down (slowing to a stop) the oil left in the pan is running to the front of the pan leaving the pump sucking air until the car is level again.

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...Dennis
The '69 (http://chevelles.com/showroom/fine69_03.jpg) & the '96 (http://chevelles.com/showroom/fine69_02.jpg)
Team Camaro (http://www.camaros.net)
Camaros Limited (http://www.camaroslimited.com)

Craig,
Had the same problem/symptoms on a 400 I built. Everything was new (crank, rods, pistons, rings, bearings, heads, HV/HP oil pump, etc.). Exact same symptoms. I pulled the pan. Oil pump pick up was ok so I replaced the oil pump (std pressure) and new pick up, and was careful to measure clearance to the pan. Same problem! Ultimately after many frustrating days I could only believe the oil restrictors I placed in the lifter valley could be the culprit. I pulled the intake removed the restrictors and solved the problem. Too much oil was being held in the top end of the engine and starving the pump. This may have been a fluke or a symptom of a SB400.
Good luck in your quest.
Ed C.
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70SS 396/350 4 speed red/white
70 LS6 4 speed blue/black under resto.
00 C5 6 speed yellow.

The dipstick could be reading wrong for a number of reasons.
I'd dump the oil and count the quarts going in to give a full reading. Then compare this to the manual.
Sounds like low oil to me.

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Make it the way you like it, forget what the other guys say!
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http://www.angelfire.com/al4/alcamino64/index.html

Craig, is it a mechanical or electric guage? If it's electric you might try replacing the sending unit. I just replaced one ($11) because of low/no pressure at idle and that did the trick.

This same pressure problems happened to me on both a 350 and a 400. In both cases the pickup fell off the pump. My fix was to weld (brase) the pickup back on. Never happened again.

Hi! HERE IS A SHOT IN THE DARK. I HAD A PROBLEM RECENTLY THAT WAS A BIT DIFFERENT. I PUT A FRAM OIL FILTER ON MY 383 STROKER WHERE I USUALLY USE AC DELCO. I WOULD GET LOW OIL PRESSURES AT IDLE AND COULD NOT GET OVER 40 POUNDS OF PRESSURE ON ACCELERATION. CHANGED OIL FILTER TO AC DELCO ALL MY OIL PRESSURES RETUTNED TO NORMAL. 30 POUNDS HOT IDLE AND UP TO 70 POUNDS ON ACCELERATION, AND YES GET RID OF THE CHEAP OIL GUAGE.