Right oil viscousity for car with oil pressure problems?

Hi, I've got a 1978 Buick Regal with a 231 cc 3.8liter Buick V6. It appears to have a problem with low oil pressure. The "engine" light would start flickering at idle speed after it had been driving on the
highway for more than 10-15 minutes. Also, in recent months I started hearing some noticeable ticking noises soon after starting the car- they usually went away after a bit. An oil pressure test read about 10 psi. The possible causes included bearing wear and worn oil pump, both of which my mechanic deemed too costly to be worth fixing on an old car.
My mechanic recommended I switch to 10W-40 and add STP. This made the light-flickering go away but not the startup ticking/tapping noise. Lately, the motor has started making much louder tapping noises at startup that take much longer to go away. It seems to be connected with cold- it started with the first really cold mornings and seems worse the colder it is. My thought is that the combo of 10W-40 with the superthick, gooey STP has raised the startup viscousity so high that when its cold the oil is so thick that it has trouble circulating properly. I'm thinking of switching to lower viscousity again- 10-30 or 5W-30 without STP.
This would of course bring back the idlespeed light flicker problem, but that never caused any noticeable noises, and anyway I dont go out of town much in the winter. Does this seem like a good idea?
Also, is the oil pump really very costly to replace on this particular model? My guess is that its the oil pump rather than bearings, anyway, as the engine has only 130K miles, sounds nice when warmed up, and has to my knowledge always been well-maintained.
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Bill Johnston wrote:

Look....you have a mechanical problem that will not be addressed by what weight oil you use. You need to either live with the noises until the engine blows up....or fix the problem.

The oil pump on these vehicles is simple to replace "as long" as the bore of the pump body (which happens to be part of the front timing cover) is not excessively scored. We never had much luck with replacing oil pumps to fix your concern, it was almost always a problem with worn cam bearings on that engine. All other things being equal, you could re bearing that engine and it would probably be fine for a long time.
Ian
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On 23 Oct 2004 14:26:54 -0700, snipped-for-privacy@yahoo.com (Bill Johnston) wrote:

I'm not a proponent of "snake oil" fixes but a product called Wynns Engine Tuneup, still available, used to work wonders quieting noisy lifters in the flat six Corvairs. You might also try switching to one of the motor oils designed for higher mileage cars and see if that brings the oil pressure up. If it works it works. If not, you are not really out anything. FWIW
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Bill Johnston wrote:

That really depends on your future plans. Do you want to keep this car for a while? If so, then it's definitely worth fixing. If you intend to get a new car soon, then make "soon" into "now" before the engine blows up. Pour in some nice thick oil, warm her up good and then drive to a dealership and trade it off your hands.
People make the common mistake of taking the expected trade in or resale value of the car, and compare it with the cost of repair, and if the repair cost is a substantial amount of the car's value, they assumed it's "not worth fixing." This is only true if you have the desire and means to get a new car, and whether it seems like other major problems are going to develop very soon. If the car is in otherwise good shape and you're happy with it, then it's just unrealistic to make that kind of worth comparison.
Once the repair bills start becoming routine and end up being close to the expense of a car payment, then it's time to consider getting a new car.

The oil pump is my guess too. Long ago I had a 89 Buick with the same symptoms you describe and it turned out to be the oil pump. Of course I too was told it was "not worth fixing" and I believed it at the time, so I put in thick oil and drove it. Couple days later the otherwise-fine-before-this engine seized and the car was basically worth scrap, instead of having a trade-in value. Big mistake on my part.
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