Oil pressure gauge "pegs"
 

1. The oil pressre gauge on my 78 300D (123), 171k miles, "pegs" the needle @ 45 lbs. Is this normal?

2. The exhaust system needs to be replaced. It would be nice if the car had a little more low-end "get up and go". Should I replace with original or something more free flowing?

The car runs good; no other serious issues...

I am new to MB and diesels. Any help/hints/suggestions greatly appreciated.

My other sleds are a restored 64 1/2 Mustang convertible and a 93 525i.

Yes, normal. That's the way they work.

I can only speak to the oil pressure question... If the high oil pressure is at idle, I would say there is a problem. In my MB's the oil pressure drops to ~1 bar (~15 psi) at idle and pegs at 3 bar (~45 psi) at around 1,200 RPM. As expected, if my engines are cold the oil pressure is a little higher at idle. If this is your recent experience, it is normal.

Also, in my opinion, you have chosen one of the best, longest lasting MB models. With proper care and feeding, the car will last a very, very long time.

Oil pressure should only be pegged once you step on the gas. Otherwise, while idling, especially in gear, it should be somewhere around .5 to 1 bar, depending on the weight of oil used.

I noticed my oil pressure gauge going down and fluctuating while I was taking some corners this morning. Is this a sign of emminent disaster?

I don't know about whether this is a "sign of emminent disaster", but I would check the oil level as a first step. Depending on how fast you going around the corner, oil does shift within the pan and it is possible the oil intake starved momentarily. Conversely, if you were going slow around a corner and the engine dropped to idle-range RPM's for a moment or two, I would think seeing the oil pressure gauge drop for a moment would be normal.

Thanks to everyone for your replies. The car is fun to drive (it takes some gettin' used to after the the 525...).

I intend to keep the car. Just fixin' up a few minor things here and there. I have found very reasonable prices at www.MercedesBenzParts.com. Does anyone have any other suggestions where to shop on-line?

Again, I am greatful to each of you...

Another quick question. Is the Shell, Rotella T, Heavy Duty SAE15W-40 a good oil for this car?

Thanks

Yes.