Use my method that I took from someone else of using sandpaper glued to a piece of glass to get the surfaces flat. You can buy a small pack of paper that's sticky on 1 side and normally use for orbital sanders.

Also, filling any pits and sanding to again get a smooth surface. The actual part may be available for not much if you want to start over. I can still buy the thermostat housing for my 78 280Z.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

My first encounter with lapping was replacing and balancing a set of Monarch injectors. Lapping has a particular method which prevents forming a taper on a subject. The figure 8 motion is recommended for small surfaces such as the two mating faces of the injector body. If they are not lapped correctly the injectors will leak.

I wouldn't imagine a piece as large as a thermostat housing would present much of a problem and being there is a gasket which does the job of sealing they just need to be good and clean. The pitting might not look good but the rubber does all the work, it seems.

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84 300SD
85 380SE
83 528e
95 318ic

What you guys can get a car fixed correctly the first time? I usually need three tries to get it right!

Well, I've sanded both surfaces of the housing. The outer one was definately warped but it's completely flat and mirror smooth now. The inner one (on the block) was more difficult and it's not as good but I don't think it was the problem. The thermostat had been replaced by the previous owner and I found minute traces of red silicone around it in various places so obviously they had been down this road before. I will also use a small bead of it on the outside of the housing. I think that that, flattening the surfaces and a second brand new gasket it should be enough to do the trick. We'll see. I'm going to wait till Thursday as I want to do it with propper daylight and I'm in the office all day tomorrow but at home Thursday.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

I stripped, stained and clear coated the wood trim in my car three times. That sounds really easy since there is less than 7sf of trim surface but actually, I installed all the trim on the door panels and installed the panels too.

The only thing I got right the first time was the bumper, flutted lower side trim, back of the exterior rearview mirrors and grille base and clear. I used just over a quart of base and just over a quart of clear to do them and did not cut and buff the finish on time. It should be a lot of fun cutting a top shelf clearcoat after a year. So there's that.

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84 300SD
85 380SE
83 528e
95 318ic

The thermostat proper doesn't use a gasket, it uses an O-Ring : https://www.pelicanparts.com/catalog/SuperCat/3202/MBZ_3202_WATPMP_pg2.htm

I've had several housings leak, usually because the flange surfaces were pitted or so uneven the rubber O-Ring couldn't get properly clamped .

As mentioned, it's a simple and inexpen$ive thing to re surface, get a sheet of 1,000 grit or finer wet/dry abrasive and use it lain on any old piece of flat glass, Rub the sealing surface in a circle 8 motion, stopping to check often, if it gets shiny in one area, the still dark area is the problem, keep at it but stop the instant you see equal markings on the surface .


Remember to wash off the crud you cleaned with abrasive before re assembly ! .

Once in a while the alloy housing will get a tiny pin hole that weeps, seeps and leaks, easy enough to fill with epoxy .

One more reason to keep your engine as clean as you possibly can .

Don't despair, the first old Mercedes I tacked the cooling system in was horrible, when I flushed it with citric acid two welsh plugs in the cylinder block began to leak profusely and I then had to replace every single steep coolant pipe along with the radiator, auxiliary water pump and God alone remembers what all else .

I also got several bad thermostats from my local M-B Dealer and some from Peach Parts too, maybe you should try a STANT branded one, I kept replacing them until I got one that gave me 82* C and the heater began to work again .

Many do not grasp that too cool is a very bad thing .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

If you still have it apart. Good time to test the thermostat in a pan of water using a thermometer. Also test the old one if still in your possession.

I have heard that the thermostat under test should not rest on the bottom of the pan though. Not certain of any effect but it does not hurt to hang if from a bar of some sort across the pan with a piece of wire. Or hang them both for a direct comparison.

If the wife has not been showing you a lot of attention lately. Usually using their stoves for other than food will usually get some.

I have already done that. And I'll use the spare O ring I bought when I bought the new thermostat.

Already done. I'll be re-assembling it tomorrow and see what happens.

- Peter. .

My heater works fine and the car doesn't run too cool. It runs at abou the right temp. It's just a bit cooler than it should be. Typically all the Mercedes I've owned have run with the temperature needle sitting at the top of the 8 on the temperature gauge. For 80 degrees. The needle never quite leaves the 8 which is fine. This one (both Thermostats) the needle only just makes it into the 8 and doesn't get further up than about half way. So it's not like it's runnin ice cold, just slightly cooler than I recall all my others running. Given that both Thermostats are like this I believe the issue is either the sending unit or the gauge itself.

I'd rather it ran cooler than hotter. I don't need any hot running engine problems in Phoenix thank you.

Any way. As I said. I'll find out tomorrow if it goes back together properly or not.

- Peter.

__________________
2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

O.K. Peter, as I said : many don't ken engine heat, a Diesel engine needs heat to run properly .

Run it hard on the freeway then get off , leave it running and pop the hood ~ if you can easily lay your hand on the upper radiator hose, it's running far too cool no matter what the gauge says .

If it's hot but you can barely touch it or you cannot hold your finger tips to it, it's fine, no worries .


Harbor Freight sells a nifty & cheap infrared thermometer but that's way over kill .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

My 1984 300D was running cool in winter, showing 60C when should be 82 C. I tested the T-stat in hot water and seemed to work, but went further and compared to a new T-stat, some Mopar T-stats lying around, a thermometer in the water and an IR gun shooting at the T-stats, I found the original one was opening a bit early and responding more sluggishly. Installed the new one and the dash gage shows 80-83 C winter to summer now. I never had trouble sealing the O-ring at the T-stat (mine has a little ear), but the inlet tube (for lower radiator hose) is a bit corroded so needed filing off the white Al-oxide. I changed the large bypass hose to silicone when I had the T-stat housing off long ago. Also change the camshaft tension spring while in there if an OM617 engine, as that spring usually wears flat on one side.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

And there you go ~

I finally got a good working ( WAHL ?) Germamnone in each of my three cars and I do routine coolant changes and the odd citric acid flush as I deem necessary .

It's good to know an American one will fit and work .

In general you want engines to run as close to boiling as possible for maximum power, fuel economy and engine life .

Older cooling systems unless in tip top shape some times have difficulty handling this .

Cool running engines are a very bad thing that's not immediately apparent .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Fixed. Haven't driven on the highway yet but basically drove around the block a few times and then took it on my work commute. The only hint of moisture is from a very tiny seep from the bottom of the upper radiator hose where it joins the thermostat housing. It's so minor it doesn't reach the road. I'll keep an eye on it and possibly just tighten the clamp by degrees to see if that fixes it. There was corrosion that I cleaned off in that location which left pitting so it's posible that a bit of JBweld to fill the pits and a new hose is warrented but for now its working fine and drivable.

The temperature still seems slightly on the low side to me but the stat is working. It's an 80 degree stat and the car reaches 80 on the line and then goes down a hair so clearly working as it should.

Relieved to have it back on the road again. When I pick up something new in a few months I'll start doing some extensive investigation into the state of the motor and see if it's realistic to start sinking time and money into it or if it's really just something I'll keep for a while as a backup.

- Peter.

__________________
2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S