i am looking to change out my thermostat in 87 420 sel, not shure which one is it, i believe it is the lower one by the alternator, if so is there a trick to getting the housing off, looks pretty tight, when installing a new one how should it be installed, i noticed another thread it said with arrow point up, the one i got is a 80C behr and don't see an arrow, any help appreciated. thanks, pics of location and or chance procedures greatly appreciated. thanks

I know there has to be somebody out there who can help with advice on changing thermostat on 87 420 sel??? THANKS

I don't know your model so I may off but it is really straightforward on my SDs. The thermostat lives in the roundish housing at the top of the motor passenger side. I think it is two or three bolts and the top of the housing comes free. The theromostat is mounted in a horiszontal position (like a top on it;s side). If you look closely at the top of the behr thermostat you will see a small arrow stamped into the metal. This is hte up position I believe. To tell you the truth I just marked my old one with a pen beacuse I pulled the whole housing off to replace the gasket on the block.
Clean the gasket surfaces as they will have some buildup on them. If it were me doing this though I think I would seriously consider doing that little bypass hose that goes between the thermostat housing and the water pump. It is a major pain to get to and just good insurance while you have the coolant drained to do the thermostat. The gasket required is another $1.00 or so for the theermostat housing to block. For this surface I used a wire wheel after plugging the holes with rags so nothing got into the motor.
then again, that little hose probably rarely blows before the longer radiator hoses...

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'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique

Dennis,

I suggest you put your queation in the Tech Help section. There are more gasoline engine guys there. We are all Diesel nuts here.

P E H