I was wondering about the difference in oil pressure behavior between a gas engined car and the turbodiesels. (I know we are talking apples & oranges here, but bear with me).

On the 300D (1984, 198,000 miles) the pressure gauge is pegged when at a cold idle, just like the V-8. Once fully warmed up, the oil pressure will be at about 1.5 – 1.7 bar at idle, again just like the V-8. On a fully warmed up engine, my 450 engine will peg the oil pressure at just barely above idle. However, it takes about 1300-1400 RPMs to get the needle all the way up to 3 on the turbodiesel when it is good & hot.

My hypothesis is that the additional flow requirements from the oil jets under the pistons, as well as the oil feed for the turbo take up a lot of flow, and the oil pump just needs a little more speed to increase the volumetric displacement enough to compensate.

Am I on the right track here, or am I just rationalizing an inherent problem with my new baby? (YIKES!)

Thanks Everyone!

thats about how my '85 300CD works. pegged at idle when cold. midway at idle when warm/hot. pegged when rpms get just above 1,000 when warm/hot.

Nic

Thanks NIC. Does your guage peg at just above 1000 RPMs, or does it require a little more when it is really hot? Also, what type (weight) oil are you using?

Thanks Again!

RTH,

More like 1200-1300 when hot and I use 15-50 synthetic oil (Mobil 1). It uses little oil (1/2 quart between 5k oil changes) and runs great so the pressure seems adequate.

FYI, my car's operating temp is between 85 and 95 degrees C depending on the weather and how hard I am driving. Never gets to 100 mark. What I read suggests that this is a bit above "normal" but as long as it doesn't hit 100 I don't plan on any immediate corrective action.

I know you are improving your new diesel. Some major items that I will do in the next 10k miles or so include replacing water pump, vacuum pump, and timing chain. May also do oil pump if not too expensive. I know I'm getting a little obsessive but its still much cheaper than a new auto and I like the car a lot.

Also, replace those little "return" lines between injectors. Made of cloth wrapped rubber. Very easy and cheap. Use the real stuff.

Nic