Stretched the overflow valve spring a couple weeks ago and I've since noticed my engine running slightly cooler. It's hovering a hair above 80, whereas previously it sat around 85. Unless I'm getting some new combustion efficiency and stepping on less pedal, I can't figure out a correlation.

Likely a total fluke, but anyone else experience this?

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1981 240D 4sp manual. Ivory White.

For those not having a cigar hose and not wanting to spend the money. Even a used one from a pick and pull. If still pliable is probably better than none. It certainly hurts nothing to have it.


This 616 engine was discontinued by the manufacturer in Europe. Then manufactured later and sold in India I think. I often wondered if any type of updating it was employed there?


How many years later it remained in production there is also unknown to me. To the best of my limited knowledge I have never seen a poster on our site that owned one of these. Indian built engines.

Lower operational temperature never reported previously to the best of my knowledge. At the same time it could be reasonable as good fuel pressure gives a more balanced power loading inside the engine.

Theoretically it does increase the actual injector timing a small amount as well I suspect. Depending on just how low the fuel pressure was before correction.

I used to have access to very expensive and specialized testing equipment years ago. It spoiled me when investigating things. Not to have access to it since.

Another oddity was some reports of an increase of 1-2 miles per gallon when changing out a really old fuel filter. To detect that I figured those posters where really anal at checking their fuel milage.

Unless the spring were so collapsed that you had no fuel pressure in the fuel rack and had extremely late injection timing as a result (you would have been seeing a good quantity of grey smoke that disappeared when you stretched the spring), it's all coincidental.

If you had enough fuel pressure in the rack to fill the injection elements to capacity prior to the stretch, then stretching the spring did nothing to the injection quantity or timing.

All things considered, assuming that the spring stretch helped in some way, diesels burn hotter with more fuel injected.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

I have speculated that low fuel pressure also may tend to reduce the fill amount in a sequential fashion.. The available fuel pressure might just fall off a little with each elements loading. The lift pump replenishes the pressure only once per revolution.

I just suspect this might occur in certain cases. I do know that when calibrating these injection pumps at a service place. They have to verify the fuel pressure to do it at.