SN95 3.8 - Showing its age

My 1995 3.8 is now starting to show signs of age. If anyone knows what these symptoms might point to, it would help out alot. I've been troubleshooting for over a month with no success. The original 3.8 was swapped out with a rebuilt short-block at 60k miles due to the head gasket problem. The rebuilt only has 70k miles on it so I'm reluctant to believe that the crankshaft or related parts could already have problems. I don't drive it that hard and i change my oil every 3-4k miles.

Here are the problems

1) There is a chirping noise that only occurs after the engine reaches operating temperature.
- I tested the problem with the belt removed to eliminate the water pump, belt and pullys. problem occured with belt off.
- Using a legth of hose, I listened to the location of the noise and it sounds like it's coming from the crankshaft.
- when i shut off the engine, the frequency of the chirp slows as the engine slows and stops when the engine stops , then a squeel starts at low level and increases in loudness slowly, then the squeel peters out quickly.

2)Oil pressure drops to nothing during idle speed - only at operating temperature
- I tested this with a gauge connected at the engine block (oil sender port)
- I replaced the two gears, a shaft, and the o-ring on the external oil pump. I didn't replace the spring or other oil pump related parts behind the timing cover.
- I let the oil pan soak in kerosene overnight hoping the problem was due to a clogged oil pickup screen.... No luck.
- Using 10w30 when problem first started. The Ford dealership recommended that I switch to 5w20. Couldn't find it so I bought 5w30. That's what I'm running now.
- Tested each cylindar compression. Result: Cyl 1,2,4,5,6 is at around 175-185 psi. Cyl 3 is low at 80-90 psi.
- Vaccum reading at the vacuum distribution tube is 16 inches. The reading flutters consistently around 3/4 inch. When opening throttle and snap shut, the reading moves to 0 then up to over 20 inches and then settles back down to 16.

My mechanic says that the engine will have to be partially dissasembled to know for sure what the problem is. That involves removing the engine. Expensive diagnosis! If its just a vaccum problem or bad seal somewhere, I'd hate to waste money on taking apart the engine.

any ideas?

- amature mechanic

figured it out

thanks for the advice. I did have a short block put in about 5 years ago due to bad head gaskets. I guess the problem could have happened a second time. That could be the problem with cylindar 3. I found the problem to the oil pressure though. turns out it was a vaccum problem. I bought new crankcase emissions lines and grommets for the valve covers. that got rid of the noise as well as the oil pressure problem. I guess the wrong vacuum affects the oil pressure when it gets up to operating temperature and the lack of oil pressure was causing a lack of lubrication and grinding on the crank shaft/main bearings. I went ahead a swapped out all the vaccum lines under the hood because they were all looking pretty bad. As I was doing that, the line feeding the heater switch broke so, they were all in bad shape. Now I need to retest compression on cylindar 3.