X3.

We have seen this condition on race cars. Start to puke after x minutes, new parts list like yours. Often we try yet another 'new' cap and it works. In some cases we go so far as to use a heavier cap. (Not that it physically weighs more, but the pressure rating is higher).

have you tested the cooling system pressure (with the "new" cap installed) and note at what point it starts to push fluid? Perhaps the pressure is hitting 15psi, pops the cap and then pushes fluid out. The indicated pressure should then be even lower as the system evacuates.


this may sounds crazy, but are the water pumps any different between the two motors? rads different? Hoses different?

What direction does the water pump turn on each motor?

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83 300TD (need rear wiper assembly dead or alive)
84 300SD Daily driver
85 300TD almost 400k miles and driven daily.
98 E300D *sold
86 300SDL *sold and made flawless 10 hour journey to new home.