When I first purchased my E300 the engine would always warm above 80C. I have been noticing that now it will not approach 80C. The fuel economy has diminished a bit so I am thinking that it is time to change the thermostat. Uh, where is the thermostat located on a 606 engine??

Follow the big lower radiator hose from the radiator to the engine and you'll run into the thermostat housing. Afterward you'll need to replace the lost coolant and bleed the system properly. You should be running at 80C or slightly above under light load when fully warmed up. The thermostat doesn't even open until 80C if it works properly.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

Passenger side, just above the alternator. You may be faced with having to replace the housing cover too since they changed the design at some point and don't make the old style thermostat. Yours might be late enough to have already been equipped with the newer style housing but I don't know that and you can ask your dealer where the cutoff was for them.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

When I replaced my thermostat I didn't have any problems with the housing. Be sure to use a new thermostat seal.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL

I've attached the page from the EPC for reference. The original housing looked like item #73 on the EPC which had the thermostat being an integral part of the housing cover, and the later updated housing looks like item 89 with the separate t-stat.

If yours looked like item 89 already then it had been replaced previously and that's likely since they updated the part several years ago. Only if your car has the original t-stat from the factory would it need the new housing. The old PN is A605 203 00 75 and the PN for the updated housing is A603 203 04 74 and it should be stamped on the housing...if you can see it without removing it, that is.

The new housing is not very expensive...only about $20 if I recall so if you need one it won't bust your bank, you just need to know that a new thermostat won't fit into the old housing.

Attached Thumbnails

 

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

I didn't know the housing used to be designed that way. Seems rather silly to me. I've had many cars and I've never seen a thermostat that you couldn't remove from the housing.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL