⟐ Answer accepted October 26, 2021 at 16:52 MST

replaced both water temp sending units on the head. Car starts and runs fine till it gets to operating temp, then it stalls and backfires. It is not running hot, water level is fine, lower and upper hoes are hot so it isn't a sticky thermostat. I'm stumped.

⟐ Answer edited June 30, 2025 at 2:41 MST

⟐ Commented May 27, 2025 at 3:37 MST

⟐ Commented July 13, 2018 at 14:27 MST

⟐ Answer accepted August 04, 2016 at 8:40 MST

⟐ Commented February 21, 2021 at 9:05 MST

⟐ Commented August 27, 2019 at 14:57 MST

My own problem is that window stop rolling down , when is 3/4 open and 1/4 left to be totally .

Can you please share some data base on your experience at this matter ?

Thanks you very much .

Mauricio Q.

⟐ Answer accepted September 05, 2017 at 17:41 MST

⟐ Commented October 09, 2025 at 6:57 MST

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.

Tom

⟐ Answered July 26, 2025 at 17:51 MST

how do I fix this problem.

⟐ Commented July 20, 2022 at 10:20 MST

thank you.

⟐ Commented June 18, 2025 at 18:15 MST

⟐ Commented June 17, 2025 at 15:40 MST

Hi Brandon, Thanks for responding. I’ve had this car

for 21 years. It’s a 1989 560SEC. When I got it the mileage was 37,400. It now has about 79,000. It looks like new inside and out and drives very well. I notice the fuel smell occasionally while driving it, but when I put it away in the garage, the smell is extremely strong. All I’ve done is to look under the hood for anything obvious. I’ve also check the gas cap and when I remove it, there is some suction. I plan on putting it up on a lift to see if there are any fuel lines leaking. There is no pool of fuel ever, even immediately after driving it.

⟐ Commented June 07, 2025 at 10:48 MST

⟐ Commented March 22, 2025 at 6:39 MST

⟐ Answer accepted October 17, 2024 at 9:08 MST

⟐ Answer accepted October 25, 2021 at 17:45 MST

⟐ Answer accepted May 22, 2017 at 18:01 MST

⟐ Commented March 16, 2026 at 2:11 MST

the problem is when its worm it doesn't start up ay all

only when its cold starts i think its the diesel pump

⟐ Commented December 22, 2025 at 9:34 MST