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85 300D turbo pristine w 157k when purchased 161K now 83 300 D turbo 297K runs great. SOLD! 83 240D 4 spd manual- parted out then junked Last edited by funola; 11-01-2017 at 09:27 PM. |
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OK, so replaced the fan clutch with one I had access to quickly. Autozone needed a week to get one. It's slightly cooler now, at least seems to hit what I will call the 90 C degree area, and not much leave that. I'm really just trying to make sure this car will make a long trip soon, as I'm moving and would prefer to drive it, than transport it.
One thing that's been mentioned a lot is "bypass mode" can someone explain this to me? What is it, and what does it do, and how is it unique from say a 1970 something Toyota?
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1983 W123 300TD US spec Turbo engine, with Euro bumpers and manual climate control, and manual transmission. |
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The way this works is that the thermostat is located with the bypass passage on one side and the cool side hose on the other. The thermostat has two poppet valves, one in the middle and one on the end, they are connected to either side of the wax motor. So as one opens, the other closes. If the thermostat fails to open, it will be in "bypass mode", meaning that water will circulate continuously around the block, but never enter the radiator. Here is a photo of a couple of Jaguar thermostats (Mercedes are essentially the same), the plate on the bottom is the poppet for the bypass passage: Mercedes adds another twist, in that the thermostat is located on the engine inlet rather than the outlet. The problem with this is that the hottest water in the engine is on the bypass side, the coldest on the inlet side. So it isn't enough for the thermostat simply to open: the speed at which it opens (hysteresis), matters. If the wax motor is too fast, then the thermostat will rapidly oscillate from open to closed and back again. I don't know if all of the third market suppliers are plugged in enough to know that. So when in doubt, the best bet is just to replace the thing. |
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This is done to reduce thermal shock when the stat opens. First a standard single valve thermostat. A thermostat located at top of engine / engine outlet coolant hose only reacts to water coming out of the engine at it's hottest point. It goes like this starting at ambient temp: engine warms up, the stat opens, hot water enters the rad while ambient temp water enters the engine, coolant temps drop, stat closes, water gets hotter , stat opens again. This first slug of cold water cause thermal shock and it hard on head gaskets for one. Using this first temp swing is a method to determine when the stat opens. In an attempt to reduce thermal shock on some cars, GM has long placed the heater outlet hose in the top of the rad outlet tank. This at least warms water before entering the engine. The thermostat closed bypass on this engine is a small bleed hole to keep some coolant flowing and isn't blocked off by the stat as it is small enough not to affect cooling. The MB or other suction side stat setups react much faster to the cold slug of water only bringing in enough to pull temps down at the stat. RE:The stat is located closer to where the cold water is coming into the engine. This reduces thermal shock to about zero. This type of system is capable of full coolant flow when the stat is closed, this setup prevents localized hot spots due to limited coolant flow found on the water outlet stat setup especially if the engine is placed under load when cold. Quote:
At first the stat is going to cycle due to a cold rad but at some point it should attain a partly open status opening farther as engine heat load increases. |
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