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Join Date: Jun 2009
Location: Santa Fe, NM
Posts: 1,035
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Oil Pressure Gauge Bouncy Bouncy Bouncy
after getting up to temp.. which I think is too hot, because of my trombone cooler, the pressure gauge gets bouncy sometimes and the needle bounces between 3.5 and 5 running steady at about 3800 rpm. Sometimes it holds steady for awhile up nearer to 5 then gets all spastic again and bounces. ? It doesn't go below 3.5 even in its bouncy times..
Fix something? or is this normal? This only happens after an hour or so, highway driving, and the temp gauge goes to about two thirds of the way hot. ?
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Scot 78 911SC coupe, sold,, 2019 Macan S "my friends all drive Porsches, I must make amends.." |
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08-17-2009, 10:34 AM
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Join Date: Jan 2006
Location: Santa Barbara, CA
Posts: 2,307
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Almost always a wiring connector problem in my experience. Undo the connector at the rear of the motor, clean carefully, replace and be sure it is securely attached. Nine times out of ten this will do it.
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jhtaylor santa barbara 74 911 coupe. 2.7 motor by Schneider Auto Santa Barbara. Case blueprinted, shuffle-pinned, boat-tailed by Competition Engineering. Elgin mod-S cams. J&E 9.5's. PMO's. 73 Targa (gone but not forgotten) |
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08-17-2009, 10:42 AM
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Join Date: Jun 2009
Location: Santa Fe, NM
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That Was It
thanks taylor,
The wire just sort of busted off completely when I went in there and touched it. Those two wires are very crispy well-done back there. I carefully stripped some back and re-connected the clip. But I should probably replace both those wires all the way back. Where do they come from? Way far in there someplace? 
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Scot 78 911SC coupe, sold,, 2019 Macan S "my friends all drive Porsches, I must make amends.." |
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08-17-2009, 05:48 PM
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Join Date: May 2004
Location: Boulder, Colorado
Posts: 7,275
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Ditto what JHT says. If you cut the signal wire for the oil pressure (or interrrupt it in any other way), the gauge will peg. I bet your '78 has a 5 bar gauge, so it is pegging. The wires on my race car seem to break, so it stays pegged. If you ground this wire it will show zero pressure. Yours sounds like it may be an intermittent connection.
It is just possible that your sender is worn out. It is just a rheostat inside, with pressure pushing a slider over some resistance wire windings. Over time these can wear through, and at some level of pressure it will look like an open and the gauge will peg. But I'd not expect your oil pressure to increase after an hour's driving. Unless you rev the motor a lot more at that point. So wiring is the first (and easiest) check no matter what. If that doesn't work, you can easily replace the sender. Easy to check the gauge (an unlikely source of this problem): pull it out, and with power on pull the sender wire off. Gauge should peg. Now ground the sender lug. Gauge should drop to zero. If all this happens, chances are the gauge is fine. Walt Fricke |
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08-17-2009, 05:54 PM
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Join Date: Jun 2009
Location: Santa Fe, NM
Posts: 1,035
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thanks Walt.. yes it was the wire.
I just went for a quick cruise, and the gauge is working just fine. Looking more normal. It was just cooked extra well done. 
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Scot 78 911SC coupe, sold,, 2019 Macan S "my friends all drive Porsches, I must make amends.." |
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08-17-2009, 06:44 PM
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