An owner selling his 84 300SD described the car as running well when warm, but it is sluggish for “a few blocks” and then it runs more strongly.

If this were a gas car, I would immediately go towards the fuel mix being off when cold, but this being a diesel - ???.

Is it possible that this is an effect of the engine compression being low due to piston/ring wear, and once the heat has expanded the pistons it then has more compression, therefore running well “after a few blocks”? Or, is there a turbo related issue, such as the wastegate blowing off manifold pressure when the engine is cold?

I know, I know, a compression test is in order – but I’m trying to boil down the selection of cars to choose from rather than compression check half a dozen cars.


THANKS AGAIN EVERYONE!

Every diesel that I have ever driven has been slightly sluggish immediately after starting in cold weather. This includes my 300D, which I had checked before I purchased and it runs 320 in all five cylinders. From my experience it is normal for diesels to be a little sluggish when they are really cold.

Don't try to drive a diesel fast when it is cold. You will damage it.

__________________
Ben

The MBs:
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K

My 300SD operates exactly the same, and any diesel will. There's a simple explanation for that coming from the Chevron website:

"When a cold diesel engine is started (cold start), the heat of compression is the only energy source available to heat the gas in the combustion chamber to a temperature that will initiate the spontaneous combustion of the fuel (about 750°F [400°C]). Since the walls of the combustion chamber are initially at ambient temperature rather than operating temperature, they are a significant heat sink rather than a heat source. And since cranking speed is slower than operating speed, compression is also slower, which allows more time for the compressed air to lose heat to the chamber walls."

Add to that the fact that the coolant add to the heat sink effect, and the car is going to run poorly (sluggish) until it warms up a bit. I just drive mine gently for the first few blocks, and keep the shifter in a lower gear to assist in warming the engine by keeping the RPM's higher.

__________________

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."