2005 e320 cdi has 150k miles and the MB maintenance schedule calls for coolant change (coolant change interval is really high....140-150k or 10 years I think).

Should I change out my thermostat at same time as a preventative maintenance measure? What is your opinion?

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-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991

If you change the Thermostat test the new one before you install it.

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84 300D, 82 Volvo 244Gl Diesel

See my posts 9 , 12 , 14 < see pic ) http://www.peachparts.com/shopforum/tech-help/355880-95-c280-overheating.html

Car was 17 years and 165,000 ish miles at the time

Note that the engine ran cold at road speed and hot at idle. The cold at road speed was due to the stat not shutting water off to the rad and the hot at idle was due to the bypass not being blocked when the stat was open so hot water went back into the engine rather than through the rad.

The thermostat and housing are a unit, the resovior needs changing when the fluid is changed. My car 05 cdi will have its 3rd thermostat they are somewhat a problematic by staying open. 230 km.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

For owners of the E320 CDIs, is your experience that the thermostats fail? Would this then be a reasonable preventative maintenance to complete when doing a coolant change? Or is it a waste of money?

__________________
-- Chris

'95 E300, 216k miles, Silver Surfer
'05 E320 CDI, 138k miles
'07 S550 4matic, 69k miles

Gone but not forgotten:

'76 300D, 350k miles?, SOLD in 1995
'75 240D, 300k miles, SOLD in 1991

If the coolant change involved removing the Thermostat ( it does not ), then go ahead and do it if you want.
If the changing of the Thermostat required the draining of the cooling system, like a low mounted thermostat on a 603, ( it does not ) then do it if you want.
Changing the thermostat is a completely separate task with almost no overlap in labor or parts. In my opinion, change the thermostat when it fails.

When we got the 2005 E320CDI home, changing the thermostat was the first thing we did. It failed open and the drive home in below zero temp. was cold. It had about 190k and there was no record of it having been changed before.

__________________
Greg
2012 S350 BlueTEC 4Matic
2007 ML 320 CDI
2007 Leisure Travel Serenity
2006 Sprinter 432k
2005 E320 CDI
1998 SLK230 (teal)
1998 SLK230 (silver)
1996 E300D 99k, 30k on WVO
Previous:
1983 240D, on WVO
1982 300D, on WVO
1983 300CD, on WVO
1986 300SDL 237k, 25k on WVO (Deerslayer)
1991 350SDL 249k, 56k on WVO - Retired to a car spa in Phoenix
1983 380 SEC w/603 diesel, 8k on WVO
1996 E300D 351k, 177k on WVO

. . . on the road at an unexpected time leaving you stranded. . .

Look at the pics of the link I posted. If the poppet valve hadn't tilted, it would have snapped shut overheating the engine.

A stat not opening is a far greater type of failure. The rubber bladder fails allowing wax to leak out of the stat motor. 2:46 https://www.youtube.com/watch?v=J7BiHSEKrII