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

If there is a little hole and a floating tiny ball, this part should be at the highest point.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

I just got done doing this not too long ago. Apparently, there were two different water pump manufacturers and they put the thermostat in 2 different locations. If the piece on the left of your water pump right by the alternator bracket has two outlets, one going up and the other going down, your thermostat is on top of the water pump, like many cars. This would be an extremely easy bolt off bolt on deal.

However, if the piece on the left of the water pump only has one outlet (which points down, where the lower hose connects to), your thermostat is behind it. A little harder to get to, you're right, very tight. In this case, I took off the alternator bracket. Just loosen the belt, slip it off, undo the cc actuator rod and set the whole works over to the side. Then I simply unbolted, switched out t-stat, and bolted back up again the t-stat housing. As Ali said, put the checkball at the 12 o'clock. Also remember to use a new o-ring. Then just bolt the alternator housing back on, reinstall and tension your belt, pop on the cc act. rod and you're done. Also remember that you'll have to drain and refill the radiator.

Hope this helps.

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'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."

I have one with the pump configuration with only one hose on the left that goes down to the bottom of the rad., on a 1989 420SEL. I'm having a tough time getting those 6MM allen key bolts out that hold the alternator bracket on. I see there are 4 bolts. Any trick to getting them out? Mine are in very tight. A bit of rust in the centre hole. I'll have to replace at least two because they are so rusty and getting rounded on the inside. I just got the two on the driver's side out. The bottom one and the one on the left side are in solid and the hex ratchet bit is starting to round them out. Any recommendations on how to get them out? I'm about to resort to the rounded bolt extractor bits.

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1989 420 SEL

Unfortunately I had to use an air hammer on mine - made a score on the bolt itself and used a screwdriver and vice grips. I also had to order an extra bolt to replace the one I had to destroy to get out. I have the part # if you need it (I think). The dealer had a time finding the correct part #.

I have a 91 with the single outlet.I did not remove alternator bracket,just the alternator.Then with 1/4 drive sockets and extension,I remove the two bolts on the neck.Really not hard at all,try to do the same on a 84 porshe 944,it took me about 5 hours on that one,with busted knuckle and a lot of @*%&#@*&*^

That was a smart idea, to cut a line into the bolt and then use a screw driver and visegrips to turn it out. I never thought of that. I presume that was a slotted blade screw driver? I guess I could cut a line using the dremel machine. I have an old epc, the part numbers that I found for a 1989 420 SEL alternator bracket bolts are: (M8x35 )000912 008098 qty 3; (M8x65) 000912 008058 qty 1. Are these correct?

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1989 420 SEL

I found the easiest way to get the rounded out allen bolt loose is to drive a 12 point 12MM socket on it and the you can back it out.