S-Class (W140) 1991-1999: 300 SD, S 350TD, 300 SE 2.8, S280, 300 SE 3.2, 300 SEL 3.2, S320, S320L, 400 SE, S420, 400 SEL, S420L, 500 SE, S500, 500 SEL, S500L, 600 SE, S600, 600 SEL, S600L, 500 SEC, 600 SEC

Thermostat

Old Feb 17, 2007 | 10:33 AM
  #1  
chuck gainor's Avatar
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From: Bethesda, MD
1995 S 420
Thermostat

The coolant temperature gauge in my 95 S420 measures about 60 degree C and does not get any higher. The coolant should be at 80 degree C according to the service department at a local MB dealer. I am still getting heat in our 10 to 20 degree F days here in the nations capital.

But I thought I wold like to change out the thermostat, although the problem could be sensors or the coolant temperature gauge.

I looked at an article posted in the forum showing how to remove the thermostat in a v 12, but wanted to know if the thermostat housing in the S420 engine is the component that the upper radiator house is attached to and held in place with bolts with Allen fittings?

Chuckg
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Old Mar 12, 2007 | 02:57 PM
  #2  
pegsneggle's Avatar
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Thermostat

Hi
My name is Mike Wood. I have just bought the same model of car as you. It's the same age and had the same problem, with the same incorrect temperature. I have just fitted a new thermostat and the temperature has risen to just over 80. It's too early for me to say what effect this has had on the economy.

The thermostat is not under the block connected to the top hose, though you are in the right area. If you look to the left of this block, you will see a short piece of right angled hose. On one side of this short hose is the water pump and on the other is the thermostat. It is held in position by 3 x 10mm bolts.

You can change it (as I had to) by just disconnecting the top part of the short hose. I was unable to free the bottom connection. It will be a struggle.

It will be worth buying some spare bolts, in case you drop one. They are each about one inch long. When you buy a thermostat it will come with the required rubber sealing ring, so there is no need to order this seperately, as I did (I now have a spare).

I would be interested to know what improvement you get in mpg. (mike.wood@mwdata.plus.com)

Good Luck

Mike Wood (Leamington Spa, England)
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