Rough idle with clicking sound
I just bought a restored Euro spec 1983 Mercedes 300D W123 that was running beautifully until last week, when I filled it up with Propel Diesel HPR, a renewable diesel that is supposed to be compatible with all diesel engines (and is marked as Diesel #2 that meets ASTM D975 specifications: http://www.dieselhpr.com/ ). Then I drove for four hours to Las Vegas from Los Angeles without any issues. It ran well for that evening after driving to a restaurant, parking, then starting again and back the hotel, where I had to park it outside on a cold and rainy night overnight with about a quarter tank left.
The next morning, I had a crazy cold start and the engine was shaking and wobbling a lot, along with the car as a result, even while I was driving slowly and definitely at idle. It eventually evened out, or so I thought. I figured it might be the Diesel HPR, so I filled it up later that day with regular Diesel #2 but the issues didn't go away the four days I was there.
I drove back to LA four days later, experiencing no issues on the highway, where it sounded and ran well. I ran the tank down until the fuel indicator went on, and then, in an effort to rule out Diesel HPR as the culprit (since it's supposed to be better for the environment), I filled it up with Diesel HPR again, thinking maybe it was just the cold in Las Vegas that caused the issues.
This week in LA, the temperature hasn't been as cold at night, even though I park it in a garage, and the issue seems to be worse. The wobbling isn't so bad once I get going, but it's there at the start and sometimes when I stop for a light. Meanwhile, the clicking sound is pretty constant, and sounds as though it's coming from the bottom of the car, though it sometimes quiets down at higher speeds and randomly at some lights. Since it was literally conking out during the cold start once I started reversing or driving slowly, I am now cold starting with the ignition lever turned up, and that hasn't really made much of a difference (just makes the clicking sound faster). Also, white smoke comes out of the exhaust during this initial starting period, and a few minutes after getting on the road, though it seems to disappear later. I've been waiting for the glow plug lights to go off, as indicated in the manual. (Weirdly, the glow plug light went on again a couple of times after the car started during the rough cold start/idle.)
At any rate, at this point, I'm not even sure if it's the Diesel HPR or something else (the cold, driving to LV) that created the issue, but am wondering if anyone has any ideas as to what the issue could be. Or does anyone have any experience with Diesel HPR and older diesel engines? I'm hoping this is an easy fix, since I just bought the car.
I'm going to take it in to get looked at, but am wondering if this is serious and urgent or if I should try it one more time with regular diesel to see if that clears up the issue. I definitely don't want to make the car worse if driving it more to troubleshoot does that.
In a perfect world, I'd like to be able to use Diesel HPR as it is better for the environment, so I'm wondering if it is even the culprit here. Thanks in advance for any advice or insight.