| Oil Issues [message #65972] |
Sun, 29 November 2009 16:42  |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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Senior Member |
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What could make oil pressure drop on acceleration, yet bounce back up just as soon as the throttle is eased up?
Yes it is full of oil. No, it is not overfull and frothing.
This behavior follows an oil pump replacement.
It does not go to zero as you would expect if the pick-up tube was sucking air. It does not seem to happen when stationary.
All brilliant thoughts appreciated.
Neil
76 Eleganza now sold
Los Angeles
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| Re: Oil Issues [message #65976 is a reply to message #65972] |
Sun, 29 November 2009 16:59  |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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| Neil wrote on Sun, 29 November 2009 17:42 |
What could make oil pressure drop on acceleration, yet bounce back up just as soon as the throttle is eased up?
Yes it is full of oil. No, it is not overfull and frothing.
This behavior follows an oil pump replacement.
It does not go to zero as you would expect if the pick-up tube was sucking air. It does not seem to happen when stationary.
All brilliant thoughts appreciated.
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Sounds strange, so I might check for a bare wire going to the sending unit or maybe the sending unit itself? Try adding a real oil pressure gauge to see what is really going on.
Good luck
C. Boyd
76 Crestmont
East Tennessee
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| Re: Oil Issues [message #65978 is a reply to message #65976] |
Sun, 29 November 2009 17:01 |
jwillard
Messages: 118
Registered: May 2004
Location: Silver City, NM
Karma: 0
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Boyd makes a good point. Make sure you actually have a problem and not a bogus reading on a guage.
Jeff Willard
Silver City, NM
1973 ex-Glacier
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| Re: Oil Issues [message #65979 is a reply to message #65972] |
Sun, 29 November 2009 17:18 |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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Senior Member |
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Thanks for the thoughts.
#1 - it is a freshly rebuilt motor. Not that that means anything.
#2 - I am compulsive enought to have a mechanical and an electric gauge. They both read the same, although the mechanical gauge does not react as fast.
I wish it was easy...
Neil
76 Eleganza now sold
Los Angeles
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| Re: Oil Issues [message #65981 is a reply to message #65972] |
Sun, 29 November 2009 17:36 |
fred v
Messages: 999
Registered: April 2006
Location: pensacola, fl.
Karma: 0
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if it happens only when accelerating then it has to be something to do with the pick up tube barring what jwillard suggested. if it is sucking air it may not go to zero. you may have to drop the pan and look.
good luck,
let us know what you find,
Fred V
'77 Royale RB 455
P'cola, Fl
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| Re: Oil Issues [message #65983 is a reply to message #65972] |
Sun, 29 November 2009 17:53 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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How about a kinked cooler line or cooler problem. Torque postioning of engine making it worse under load? Simple test is to remove the oil cooler adaptor nut and thread a new filter right to the engine. This would take the whole cooler circuit and that filter out of the equation. Could it also be a mis installed bypass spring. Allows pressure at idle then bypasses too soon. IIRC there are 3 places in an Olds to bypass including the filter. Probably something simple like that.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Oil Issues [message #65991 is a reply to message #65972] |
Sun, 29 November 2009 18:48 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Did it only happen under heavy acceleration or after a certain RPM ? Did you check the clearence of the oil pump pickup to the bottom of the pan when you installed the oil pump? It should be around 1/2" to much or too little would not be good. The pickup tube is brazed to the body if you have the press in type right?
Roy
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Oil Issues [message #66008 is a reply to message #65979] |
Sun, 29 November 2009 19:39 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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| Neil wrote on Sun, 29 November 2009 18:18 |
Thanks for the thoughts.
#1 - it is a freshly rebuilt motor. Not that that means anything.
#2 - I am compulsive enought to have a mechanical and an electric gauge. They both read the same, although the mechanical gauge does not react as fast.
I wish it was easy...
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Freshly rebuilt?? Did you supervise or was it outsourced? Does the pressure drop immediatly under aceleration or does it take a few seconds? Does it stay low or does it pick back up? Does engine temp have any effect? Did you use a high volume oil pump?? Olds 455s do not like these type of pumps due to the poor oil return system. Did you remove excess casting and debur the return holes?
I would agree to change the oil filter and see if any change.
6 qts + oil filter + oil cooler on fresh engine??
C. Boyd
76 Crestmont
East Tennessee
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| Re: Oil Issues [message #66069 is a reply to message #65979] |
Mon, 30 November 2009 08:31 |
mdryan
Messages: 27
Registered: March 2008
Location: Seattle
Karma: 0
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If oli pres doesn't drop when revving stationary then I would suspect sloshing in the oil pan.
Though not a cure, you might try adding ~ an extra quart of oil and see what happens.
MDR
Mark Ryan
1978 Kingsley
Pac. Northwest
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| Re: [GMCnet] Oil Issues [message #66074 is a reply to message #65972] |
Mon, 30 November 2009 09:09 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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Neil,
How did you determine the clearance between the pickup and the bottom
of the pan. I have seen this happen before because the pickkup was
too close to the bottom of the pan and resulted in cavitation. Before
I tack weld the pickup onto the pump body, I press the pickup
partially into the pump body higher than I know it shoud be, then put
the pan on and press down until the rails are securely against the
block (no gasket). then I remove the pan, turn the pickup tube an
additional quarter inch and tack weld in place. Your oil pressure is
behaving as if your pickup has fallen off, or you're having a
cavitation issue. Of course, if you have one of the high end bolt-on
pickups, this all goes out the window.
A quick way to check would be to remove the distributer and use an
oil pump drive and trouble shoot with the front of the coach at
different elevations to simulate oil slosh upon acceleration. The
hard way to check is to......well, you know. PITA but probably has to
be done if you're sure both gauges are correct.
On Sun, Nov 29, 2009 at 3:42 PM, Neil Martin <nmartin@hfbllp.com> wrote:
>
>
> What could make oil pressure drop on acceleration, yet bounce back up just as soon as the throttle is eased up?
>
> Yes it is full of oil. No, it is not overfull and frothing.
>
> This behavior follows an oil pump replacement.
>
> It does not go to zero as you would expect if the pick-up tube was sucking air. It does not seem to happen when stationary.
>
> All brilliant thoughts appreciated.
>
>
> --
> Neil
> 76 Eleganza
> Los Angeles
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
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| Re: Oil Issues [message #66077 is a reply to message #65972] |
Mon, 30 November 2009 09:37 |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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Senior Member |
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Thank you for the guidence. I will bring these thoughts to my mechanic and keep you all up to date on the results.
Neil
76 Eleganza now sold
Los Angeles
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| Re: Oil Issues [message #66079 is a reply to message #65972] |
Mon, 30 November 2009 09:49 |
Neil
Messages: 271
Registered: July 2007
Location: Los Angeles and Magalia, ...
Karma: 1
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Senior Member |
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Let me also answer Charles' questions
"Freshly rebuilt?? Did you supervise or was it outsourced?"
Outsourced
"Does the pressure drop immediatly under aceleration or does it take a few seconds? Does it stay low or does it pick back up? Does engine temp have any effect?"
I warmed it up before going out for a drive. I did not notice this drop while reving it in the driveway. It picks back up upon lifing the throttle - like it is responding to vacum. Could a bad pvc valve do this?"
"Did you use a high volume oil pump?? Olds 455s do not like these type of pumps due to the poor oil return system. Did you remove excess casting and debur the return holes?"
I did have a high volume pump put in after the initial build had what I thought was insuffficient pressure. No work was done on the return holes.
Neil
76 Eleganza now sold
Los Angeles
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| Re: Oil Issues [message #66182 is a reply to message #65972] |
Mon, 30 November 2009 19:46 |
philipswanson
Messages: 282
Registered: January 2004
Karma: 0
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Senior Member |
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The easiest way to check the pickup screen clearence, pull the drain plug, stick a small inspection mirror in the hole and have a look. With flashlight in hand of course. The ideal way would be to use a bore-a-scope. If it fell out, you will definitly see that too.
Phil Swanson
77GMCPB
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