This is true. But the more likely explanation is that the car would have been running "on the thermostat" due to ambient conditions. This could be due to mild air temperatures, and/or the efficiency of the fan and radiators.

Some gas engines used a 167F/75C degree thermostat. It is a Stant 13496 or NAPA THM-47. The thermostat is physically identical to the diesel thermostat except the bypass plate on the bottom is 1.7" in diameter as opposed to the smaller 1.46" diameter bypass plate on the diesel. Any idea if that thermostat would work in the OM617 motors?

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'82 300D - Light Ivory, 2nd Owner (Back in the wind April 2013!)

'95 E300D - White, grey interior. (Suffering from stuck/broken glow plugs)

Deuteronomy 22:4-
"Thou shalt not see thy brother's ass or his ox fall down by the way, and hide thyself from them: thou shalt surely help him to lift them up again."

Since the 1930's, it's been known that engine wear increases with decreasing temperature. You really don't want to go less than 180.

HOTRODSRJ’s COOLING TIPS Operating temperature vs power and longevity!

Removing the thermostat entirely leaves the bypass wide open, depending on the characteristics of the thermostat housing, you may have preferential flow through the bypass. This is why some engine will overheat without a thermostat.

Bottom line is the bypass system is designed to put the water flow where it needs to be to keep the engine in its comfort zone of design operation. It puts the coolant to the radiator when the engine needs cooling, and it flows it back to the block, bypassing the radiator when the engine needs to come up to optimal operating temp. When you remove such a bypass stat you get coolant always being split between the radiator and the bypass back to the block. This results in it running cold in cold weather and hot in hot weather. In moderate weather and operating conditions I suppose it might be fairly ok.

Removing it would only be a benefit if you find it stuck in bypass mode and need to do a stop gap measure to get by for a day or two while sourcing a stat. (Some cooling being better than none).

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.