Today's D'oh! moment
Thread Starter
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
Today's D'oh! moment
For some time I've fretted about the oil pressure in my '71 454. Engine is fresh and should have good pressure but when the engine got thoroughly warmed up the idle pressure would nose dive to less than 10 PSI. Last year I switched to 15W-50 oil and it helped a little. I also raised idle speed to 900 rpm and it indicated 25 PSI hot idle. At cold start high idle it would indicate 50 PSI.
Well, today it finally occurred to me that maybe, just maybe, the gauge could be inaccurate. The bright ones among you can probably already see where this is headed.
Took the gauge out and hooked it up to 50 PSI of compressed air. Gauge indicated 15 PSI. Yes, 15 psi.
Calibrated it to where it would read within 2 PSI at the marks, 17.5, 35, and 52.5 PSI.
Re-installed the gauge and fired it up. Instead of 50 PSI it now reads off the scale. Past 70, I guess about 80 PSI. And that's at 1200 rpm!
I'm going to go back to 10W-30 oil and see if it calms down a little. It's time for an oil change anyway.
But that's what I get for breaking one of my own rules: always check your measurements before making any changes. Lesson (re) learned.
Well, today it finally occurred to me that maybe, just maybe, the gauge could be inaccurate. The bright ones among you can probably already see where this is headed.
Took the gauge out and hooked it up to 50 PSI of compressed air. Gauge indicated 15 PSI. Yes, 15 psi.
Calibrated it to where it would read within 2 PSI at the marks, 17.5, 35, and 52.5 PSI.
Re-installed the gauge and fired it up. Instead of 50 PSI it now reads off the scale. Past 70, I guess about 80 PSI. And that's at 1200 rpm!
I'm going to go back to 10W-30 oil and see if it calms down a little. It's time for an oil change anyway.
But that's what I get for breaking one of my own rules: always check your measurements before making any changes. Lesson (re) learned.
Le Mans Master
Joined: Apr 2011
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From: Hermosa
I think if it was mine I would try to verify your new readings with another gauge. Wouldn't have to be one for your corvette just one that could be hooked up to the line to confirm readings of one good gauge to a possibly questionable one.
If you're getting 80 psi at 1200 rpm seems like it would have been blowing oil past seals at any kind of operating rpms.
If you're getting 80 psi at 1200 rpm seems like it would have been blowing oil past seals at any kind of operating rpms.
Race Director
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From: Corsicana, Tx
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How did you calibrate it? This is the electric gauge? How about the sender??
Is that a stock pump with a high pressure spring?
JIM
Is that a stock pump with a high pressure spring?
JIM
Thread Starter
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
Well, the in-car gauge is now calibrated against 2 other gauges, so I trust it. 80 PSI is not out of line, that's where the pressure relief valve opens in the pump. I have a high-volume pump (which is probably overkill for my application). That and the 15W-50 oil would explain the readings.
I should have suspected the gauge as soon as I saw it reading only 50 PSI @ 2000 rpm cold.
I should have suspected the gauge as soon as I saw it reading only 50 PSI @ 2000 rpm cold.
Thread Starter
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
Jim: It's the factory mechanical gauge. I removed it from the cluster and hooked a hose to it. The other end of the hose to a 5 gallon air-tank. The air tank has a tire valve on it so I could hook the gauge to the tank and check the pressure with a tire-pressure gauge at the same time. I filled the tank to 17.5, 35 and 52.5 PSI as those pressures match the tick marks on the gauge.
The pump is a HV-HP melling. A regular pump would probably have been a better fit.
BTW, your profile still says Houston, TX. Time to update?
The pump is a HV-HP melling. A regular pump would probably have been a better fit.
BTW, your profile still says Houston, TX. Time to update?
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
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I LIKE oil pressure. HV is fine. HV doesn't necessarily make any more pressure..it just gets there quicker.
I had my gauge stick one time way pegged over past 80 psi when cold. I made a little block to keep it from going past 80 that seemed to help. Been fine for years since I fixed it.
Yep....never got around to updating it when i moved to Ft Worth!
BTW...what's this white stuff on the ground anyway???
JIM
I had my gauge stick one time way pegged over past 80 psi when cold. I made a little block to keep it from going past 80 that seemed to help. Been fine for years since I fixed it.
Yep....never got around to updating it when i moved to Ft Worth!
BTW...what's this white stuff on the ground anyway???
JIM
Le Mans Master
Joined: Oct 2010
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From: melbourne florida
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a melling pump is one of if not the best pump you can get. i have always used melling pumps and never had an issue.
Last edited by 7t9l82; Feb 10, 2013 at 07:44 PM. Reason: spell check
Team Owner
Joined: Jul 1999
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From: Orange Park Florida
OH, do I have a funny story from maybe 35 years ago on this topic, my second car was a full race Pontiac engine '61 Catalina fastback 2 dr ...and so the engine had more clearance than Clarence.....the pistons were SO loose that one of them tapped a tad, no sweat, 50k miles of abuse and still ran strong.....the chick it sold it to in Texas in '70 is probably STILL running from the cops with it......
BUT the trick was that because of the loose race clearances I ran some heavy oil to keep it happy.....until.....
one winter overnight storm it went to ZERO out, and that engine would NOT crank, period....tried TWO batteries in series, 24 volts to the starter just 4X the power........no go....
finally built a FIRE under the crank case to heat the POS SOB up enough to turn over.....and so to drain the oil for something more reasonable than 20-50 with 3 cans of STP GOO in there.....
been a while....this all about '68? or so.....
BUT the trick was that because of the loose race clearances I ran some heavy oil to keep it happy.....until.....
one winter overnight storm it went to ZERO out, and that engine would NOT crank, period....tried TWO batteries in series, 24 volts to the starter just 4X the power........no go....
finally built a FIRE under the crank case to heat the POS SOB up enough to turn over.....and so to drain the oil for something more reasonable than 20-50 with 3 cans of STP GOO in there.....
been a while....this all about '68? or so.....
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Drifting
Joined: Mar 2011
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OH, do I have a funny story from maybe 35 years ago on this topic, my second car was a full race Pontiac engine '61 Catalina fastback 2 dr ...and so the engine had more clearance than Clarence.....the pistons were SO loose that one of them tapped a tad, no sweat, 50k miles of abuse and still ran strong.....the chick it sold it to in Texas in '70 is probably STILL running from the cops with it......
BUT the trick was that because of the loose race clearances I ran some heavy oil to keep it happy.....until.....
one winter overnight storm it went to ZERO out, and that engine would NOT crank, period....tried TWO batteries in series, 24 volts to the starter just 4X the power........no go....
finally built a FIRE under the crank case to heat the POS SOB up enough to turn over.....and so to drain the oil for something more reasonable than 20-50 with 3 cans of STP GOO in there.....
been a while....this all about '68? or so.....
BUT the trick was that because of the loose race clearances I ran some heavy oil to keep it happy.....until.....
one winter overnight storm it went to ZERO out, and that engine would NOT crank, period....tried TWO batteries in series, 24 volts to the starter just 4X the power........no go....
finally built a FIRE under the crank case to heat the POS SOB up enough to turn over.....and so to drain the oil for something more reasonable than 20-50 with 3 cans of STP GOO in there.....
been a while....this all about '68? or so.....
Problem solved. Ran like a champ after that.
Thread Starter
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Exactly. That was all that was needed. The sweep was correct, it was just the needle that was in the wrong position. I had it apart a few years ago as sanding dust got into it when doing the body work and the needle got stuck. I must have installed the needle in the wrong position when I reassembled it.
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
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You can shim a stock pump to put out more pressure.
A HV pump just gets to whatever pressure it is set to quicker. Like higher idle oil pressure...higher low speed pressures...but the actual peak pressure at high rpm will be the same as any other pump with the same spring setup.
Those stories often start when someone builds enough performance/rpm into a package to the point a much better design pan is needed...not necessarily bigger. Usually windage issues cause more issues than drainback.
JIM