Hello,

I have just bought a 91 Stealth ES DOHC. When the weather is cold out (below 30 degrees) when I start the car, there's a rapping from what sounds like the bottom end. It goes away after 30 seconds or so and doesn't come back again. When the car has been sitting all day and the temp is above 30 degrees outside, or when the engine is warm, no knocking at all. I can leave the car for days, come out and start it if it's not cold outside, and there's no noise.

Is this a sign of oil pump problems, poor choice of oil, or a more serious engine problem (bearings)?

What weight oil are you running? If you are in fact "knocking" at startup, that is a bad sign.

I'm using 10/30 in the car right now. It only happens when the outside temperature is below freezing and ony till the oil pressure comes up to the line. Someone where I work suggested Lucas oil stabilizer, but I'm reluctant to try it if I'd be covering up something major and not just a lack of lube at start.

Thankfully, my mechanic says its coming from up top, not in the bottom end :)
Still, not the greatest news [&o]

You may want to try an oil with a better cold weather viscosity. What weight are you using now? During the cold winter months, it can get between 20-30 degrees where I live. I usually switch to 5W30 when it gets cold. I had a similar problem to what you're describing and since I switched, all that disappeared.

I'd try an oil flush first I've seen numerous cars have loud noises at startup due to clogged passages ... A simple oil flush may take care of it ...