Need to remove the thermostat to do a quick test without it. Where is it and how easy to remove it? I do a search and it seems to be a PITA to remove. Any tips?

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

Just above the alternator. I don't remember it being too hard.

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James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k

Location= passenger side / front near the bottom of the head. You can do it by just reaching from under the car....No need to pull the alternator but you will need "snake" like arms and hands. Tough to get it back in, gasket and all, from that angle.

Easier though from the top if you pull the air filter box (2 nuts), and air hose (2 clamps) runnng to the turbo. Bingo...plain sight! Just a few 10mm nuts and a philips screwdriver.

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1986 300SDL 440,xxx

Without the thermostat in place, the coolant will not flow normally. Here is a quote which I saved:

OM603 Coolant flow path, from Brian Carlton
The coolant that returns from the radiator heads to the thermostat housing. If the thermostat is "closed", it stops right there and can't go to the water pump. All coolant comes from the crankcase and passes the flat disc which is wide open.

If the thermostat is partially open, some of the coolant from the radiator passes through the thermostat body and out to the water pump. Some of the coolant from the crankcase also passes the flat disc at the rear of the thermostat and also goes to the water pump.

If the thermostat is fully open, the flat disc closes the passage from the crankcase and all the coolant from the return line from the radiator passes through the body of the thermostat and onto the water pump .

Getting back to your question: thermostat removal.
I remove the thermostat by first removing the bellows from the air flow box to the turbo intake, this permits access to the 2 10mm bolts. I find it helpful to use a small air wrench.