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Old 08-31-2001, 06:45 PM
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Join Date: Jul 2001
Location: Western Michigan
Posts: 1,080
Thermostat and housing

I have two questions about the thermostat and its cover for a 1997 E320 (104 engine). Thanks in advance.

1. What size of star socket is needed to remove the cover? I found these are not hex bolts but with star heads.

2. Will a thermostat for the W124 (90 300E) fit this car? I found in a store catalog that both the W124 and W210 share the same thermostat number but MB has two different parts numbers.

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Old 08-31-2001, 07:51 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
The thermostat for all m103 and m104 engines should be the same.

I think you can go to a local parts store and pick up a set of sockets that are labeled E6-E10 for the star configuration. I left mine at work and needed them at home. I purchased a set for $15.00 at AutoZone.
Donnie Drummonds
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Old 08-31-2001, 11:16 PM
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Join Date: Jul 2001
Location: Western Michigan
Posts: 1,080

Thank you so much.

I'd like the temp to be a little higher. It is now around 80 degrees C and I want it to be in the 87 degree mark.

Maybe you can answer this question. Why old MB thermostats always get in that not fully closed position? In my other two cars, I have replaced the thermostats on both and both times, the temps were not high enough. After a thermostat replacement, the temp went right up to 87 degrees.

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Old 09-01-2001, 10:24 AM
Join Date: Jul 2001
Location: Old Lyme, Connecticut
Posts: 3,596

The Mercedes-Benz cooling sytem design has a double acting thermostat. The point of the design is to avoid rapid, very high temperature changes in the water being circulated in the block and head. For example the radiator starts the day at ambient temperature which may be below zero, while the thermostat control that opens when the engine reaches its normal operating temperature, near two hundred degrees (F). Injecting zero degree water onto hot metal could cause the metal to fracture if not right away, then after a number of cycles.

The MB thermostat has two moving elements, that coordinate to make the water coming from the radiator mix with an appropriate amount of water coming from the hot engine to as it enters the water pump and gets sent to the engine. If the system gets old these two items get out of their coordinated movements, as happens to me and has happened to you, the engine never warms up. It usually happens after 70k miles or more for me so I just accept the fact that every so often I buy a thermostat and replace it. There is virtually no other explanation for the problem of not heating up right, as the engine running is surely making enough heat. Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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Old 09-01-2001, 10:34 AM
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Join Date: Jul 2001
Location: Western Michigan
Posts: 1,080

Thanks for the clear explanation. I looked the cooling system diagram and think your explanation is correct.

I found 60k miles is the point that a fresh thermostat is needed to endure optimum coolant temperature. I happen to have a spare thermostat for a 300E (bought 3 at one time and replaced two on two 300Es) and will replace the one in my W210 (58k miles).

Thanks again.

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