No, that's incorrect. Those of us living in hot climates have been dealing with this problem for years. What the OP did is spot on and proven by his results.

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CENSORED due to not family friendly words

I'm with MxFrank on this one. But as a check I'd want to see a flow meter or temp gauge on this additional line. My guess is that the line is flowing from the rear cylinders into the mixing area rather than providing cooler water to the rear cylinders.

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Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]

Can you elaborate? MxFrank's flow picture seems to indicate that if the line is fitted to the port on the housing that dieselmeken drilled and tapped, the flow would push mixed coolant through the water pump scroll and then theoretically also into this hose.

If the line is flowing from the rear cylinders into the mixing area as you suggest, then that pressure differential would promote cooling to the rear cylinders by pulling coolant through the front cylinders to the rear faster.

It seems to me that one way or another this mod improves cooling. Dieselmeken isn't exactly a novice with these engines, either.

I'd love more information if you, SL, or MxFrank can provide some, as I'm no expert. Thanks to all for engaging in a valuable discussion and sharing information!

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1983 300D Midnight Blue
4 speed, W115 intake mani, non-EGR exhaust mani, KKK K26, 3 pc Euro bumpers, Lo-spec Euro headlights, AL129X, hubcaps, custom A/C

1987 300TD Smoke Silver
Euro headlights, thermostat relocation, coolant bypass mod, rebuilt Becker + Jehnert + Helix audio, OEM Oris roof boxes and surfboard racks, Euro towbar

1983 300TD Reed (Moss) Green / Dark Olive MB Tex Euro spec

1983 300TD Silver Blue / Blue cloth Euro spec, OM648 and 722.6, 15" hubcaps, W126 S2 brakes

The water pump is pushing water directly into that tapped line coming off the thermostat housing and pushing water to the rear cylinders. I've read it's supposed to help avoid hot spots on the rear cylinders and since it's pushing water through from the cold side I'm sure that helps as well. I didn't come up with this mod but it has been put to use for many years with the Super Diesel guys and multiple company across the pond sell it for god reason. It's been tested so I don't really need to question or wonder if it works.