My oil pressure light flickered. Turned out my oil was low and the wire was loose! I added oil and jiggled the oil pressure sender wire. Problem fixed (oil light comes on with all the other dash lights, but only briefly. My questions are, if the oil pressure were low, besides checking the dipstick, how would I know if the oil pump was defective? What are other symptoms of a bad oil pump? How would a defective oil pump cause changes in the dipstick?

"...if the oil pressure were low, besides checking the dipstick, how would I know if the oil pump was defective?"

It seems that you're asking, "If I have low oil pressure, how can I tell if it's due to a bad pump?"

First, you need to determine whether or not your pressure is low. To do this, you need a gauge installed in place of the oil pressure switch. Then you can watch the pressure as a function of temperature and engine (pump) speed.

When you have a worn engine, you typically see good pressure with cold oil (viscous oil), but the pressure drops as the oil gets hot. Also, you'll see low pressure at idle but increasing with increasing engine speed.

If the pump is bad, you'll see less increase with engine (pump) speed increase and less drop with increasing oil temperature.

Keep in mind that oil pumps rarely fail. I had about 350k miles on an '82 with the original engine and pump -- and never had any indication of low oil pressure.

"What are other symptoms of a bad oil pump?"

No oil pressure would be an excellent sign of a bad pump.

"How would a defective oil pump cause changes in the dipstick?"

No effect. Oil level (if that's what you mean by dipstick) and oil pump condition are independant. Your engine (oil pump) will continue to produce the same oil pressure with increasingly low oil until the pickup starts sucking air.
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Don Foster (near Cape Cod, MA)

I have the symptoms you describe, Don - idle normal when engine is cold, no oil pressure light on. Once she warms up after 15 or 20 minutes the oil pressure light is on steady whenever the car is at idle and idle tends to be (according to the on-board tach) 500-550 - but always turns off immediately when I accelerate (as soon as I press the gas pedal).

Are these simply signs of a worn engine? A blown delivery tube o-ring? Are the oil pressure light and idle related?

If you have heard me on this before, I am sorry - I am just trying to solve this annoying problem. Thanks.
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Darius in Albany NY '86 744 GLE (172K); '91 745T (161K)

First, be sure it's not a bad wire (worn insulation) at the sender. But by 1991, Volvo had solved that problem.

If the wire's OK, then I'd be suspicious of a worn engine OR a bad O-ring on the delivery tube. I have to say that I've not heard of the O-ring problem on newer engines.

Also, you must confirm that the sender is responding accurately. For this, you should arrange to install a real pressure gauge (on a 6'-8' hose so you can see it while you drive). Then you can accurately monitor the pressure under differing conditions.

161k isn't much. My '91 740 has about 235k, or so, and we see absolutely no indication of a hot oil pressure problem.

And also.... 550-600 rpm idle is a tad low. I'd expect it to be more like 850.
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Don Foster (near Cape Cod, MA)