replace thermostat on 1987 420 SEL - PeachParts Mercedes-Benz Forum

RKreutzer · #1 10-05-2002, 10:48 AM

Hi, everybody
I would like to replace the thermostat on my '87 420. I looked at the CD and the archives but could not find a good removal description. I can see the front and top bolts of the thermostat housing but not the 3rd in the rear. I have a hard time to imagine how to get that rear bolt out without removing pieces to the left. I assume the top radiator hose has to go and that will provide more access but it doesn't look like enough space. Is there a special wrench?
Do you get to it from below?
If anybody who has taken it out on a 420 could tell me if and how it can be done without removing other parts first, it would be appreciated.
Also, the archives are mentioning anti-seize compound when installing. Is there a lubricant like WD40 recommended for removal to avoid broken studs?

Thanks for your help.
Reinhard Kreutzer

MikeTangas · #2 10-05-2002, 11:21 AM

Haven't done it on a 4.2 but have on a 4.5 and a 5.6 so the set up is similar. To get the third bolt, the hidden one, start under the car and come in from behind with a 10mm socket and extension (1/4" drive set). You might need a universal joint too depending on how tight the other accessories are to the housing.

420 · #3 10-05-2002, 11:47 AM

I was going to replace the t-stat in my 89 420SEL. I noticed that the service CD showed 2 different types of housings. One on top of the water pump and one on the side of the pump(passenger side). I assumed that the T-stat was on the top.....so I removed the upper radiator hose, and removed the 3 bolts and the cover came right off. But my T-stat wasn't in there!

It's on the side of my water pump which will require a complete draining of the coolant and it looks like I'll need to remove the alternator too to get at it. I'm just going to do it next year when I replace all belts & hoses. So don't be surprised if you take off the top of your water pump and the t-stat isn't there.

RKreutzer · #4 10-05-2002, 01:14 PM

Thanks Mike and Clay,
I am talking about the side cover as I believe Mike is.
I was afraid I might need to remove the alternator, thats why I asked. I will look at it from below and see whether I can see that bolt. I have a 1/2" drive torque wrench which, with my luck, will not go there.
The CD says only: 1. remove hose, 2. remove cover (3 bolts) 3. remove thermostat.
I assume they meant the lower hose, right?
Thanks again
Reinhard

william rogers · #5 10-05-2002, 02:48 PM

it's real easy if you take the top housing (thre 13mm bolts easy to get at)off with the thermastat housing attached ,then you can simply take the three 10mm bolts out of thermastat housing pull thermastat out and put in the new one and put it back together as a unit ,make sure you have a new gasket for the top housing.I would use anti seize on all bolts and a good soaking with pentrating oil, WD stands for water displacing and is not really a penitrating oil.........
William Rogers.......

MikeTangas · #6 10-05-2002, 03:57 PM

1/2" is way too big, 3/8" is iffy due to the tight quarters between the housing and block 1/4" works great. Yes, you'll have to drain the coolant, but you don't even have to remove the lower radiator hose if you're careful. Just the 3 bolts and off comes the housing (still attached to the hose), swap t-stat and o-ring, put the housing back together top off with coolant and water.

RKreutzer · #7 10-05-2002, 06:19 PM

Thanks William and Mike,
I don't think I can take off the top with the thermostat housing attached. That, I think, leads to what Clay describes.
I think Mike describes the set-up I have. The lower hose comes up from the passenger side lower radiator and goes vertically into a housing that is attached on the passenger side of the waterpump. 3 10 mm bolts at the 12 o'clock 4 o'clock and probably 8 o'clock position when looked at from passenger side. I see Mike's point where you leave the housing attached to the hose and just bend it to the pass. side. Now I didn't slide under the car yet to try to locate that third bolt. I let you know once I have done that. I'll check with my neighbor about that 1/4" drive.
The draining of the radiator is very simple and would leave at least that lower radiator hose empty at the pump level.
Thanks again.
Reinhard

afmcorp · #8 02-07-2003, 02:12 AM

hello 420 i just found this thread and i must say that i like what you did with your 420.

a couple of questions.

after adding the shocks and pad modification and with the lower appearance how does it really compare to the overall handling of the car did you find a plus, minus or same as type feel??

i really got to say that your look appeals to me almost as much as the 560sec. clean lines, super wheels and you seem to have hit on a good front end appearance with the euro lights and the black grille.

can you tell me a bit more about the wheels? where did you get them and exactly what the name is.

i've been searching for that look and i think you've hit on it. i got a black 88 for me which is the one i want to spruce up a mite and a gold one for my wife which i'm leaving stock. "old ladies" car if you will.

anxious to hear back from you.
tks
craig