w116 300sd Thermostat Housing

[xaliscomex]

Own a 1979 300sd (w116).

The thermostat housing (6172002415) is pitted/corroded at the inlets/outlets.
Although the rubber hoses are properly secured and tightened using good clamps, coolant continues to leak out.

I drained the coolant and replaced all coolant hoses approximately 6 months ago and I was surprised to see encrusted buildup at joints between the hoses and the metal openings (inlets/outlets) to the thermostat housing. Obviously, the buildup throughout the years is responsible for such corrosion/pits.

I thought about using some type of epoxy to smooth out the pits and even out the corrosion so that the hoses can get a tight fit but I wanted to know if anyone out there has encountered this problem before and what is the best way to handle this.

Before I go out and by a brand new thermostat housing, is there a better way to smooth out the pits or a better way to secure the hoses so that future coolant leaks can be prevented.

Also was wondering if I should use a silicone piece of hose (42mm) instead of a rubber hose between the thermostat housing and the metal line located directly under. Thats the area where I'm getting most of the coolant leaks. Hope I'm describing the area correctly. A short rubber hose (42mm) secured with two clamps on each end allows the coolant to flow thru.

Any advice is greatly appreciated

[Squiggle Dog]

Ha! I was just thinking that I wouldn't mind replacing my thermostat housing with one from an early W116 300SD that doesn't have the thermo vacuum valve switch on it.

I'd say something like JB Weld would be your best bet, if you get it level and smooth. Baking soda and vinegar with a brass brush seems to work pretty well for cleaning corrosion. You can probably even soak it in oxalic acid (wood bleach) or oven cleaner.

If you Google MTC 3829 (Mercedes part number 6172002415), you'll find what may be a compatible new thermostat housing, and apparently without the hole for the thermo switch, but it lacks the hole for the auxiliary fan temperature switch, so you'd probably have to use part of your old housing, if it's even still good. It's pricey at about $90, though.

[xaliscomex]

Originally Posted by Squiggle Dog

Ha! I was just thinking that I wouldn't mind replacing my thermostat housing with one from an early W116 300SD that doesn't have the thermo vacuum valve switch on it.

I'd say something like JB Weld would be your best bet, if you get it level and smooth. Baking soda and vinegar with a brass brush seems to work pretty well for cleaning corrosion. You can probably even soak it in oxalic acid (wood bleach) or oven cleaner.

If you Google MTC 3829 (Mercedes part number 6172002415), you'll find what may be a compatible new thermostat housing, and apparently without the hole for the thermo switch, but it lacks the hole for the auxiliary fan temperature switch, so you'd probably have to use part of your old housing, if it's even still good. It's pricey at about $90, though.

Was recommend that I use Permatex PermaShield Gasket Dressing/Flange Sealant and good solid hose clamps. Hopefully that works. If it doesn't work i will have to buy a brand-new one from the dealer. The good thing is that the thermostat housing is still available from the dealer.

Will clean up the area using one of your recommended methods. Thanks.

Will be a while before I get my car back on the road.
The Master Cylinder had been leaking brake fluid inside the booster which damaged the diaphragm. Previous owner had someone use sealant between the MC and the brake booster.

I removed the booster over the weekend and will be getting it rebuilt by a recommended shop in Upland CA.

[xaliscomex]

Cleaned up the thermostat housing as much as I could and used PermaShield Gasket Dressing/Flange Sealant by Permatex on the hoses.

I refilled the car with distilled water and Zerex G-05 Coolant (concentrate) and then reconnected the battery cable. As soon as I reconnected the neg battery cable I immediately noticed the Servo making its "dizzy" noise. I thought that was weird because it's been more than a year since I had heat and I was certain that my Aux water pump, Servo or AC amplifier had gone out.

I turned on the car and parked it on my inclined driveway to bleed the air out of the cooling system. I left the car on for approximately 7 minutes (with cap off the reservoir coolant tank) and checked on it every couple minutes. I then decided to press the push buttons on the ACC climate control panel and to my surprise, I immediately felt heat coming out of the vents. I couldn't believe it. HEAT!!

Not sure if flushing the coolant dislodged something that was stuck inside the servo.

Maybe someone here knows what might of happened.

While I was cleaning the thermostat housing and replacing hose clamps and I also ended up taking advantage of my car being stuck in my garage and decided to remove my rusty brake booster. I mention this because the only other thing that I messed with was all the cables and wires that are located behind the instrument cluster. Highly doubt that moving any of those wires would have triggered the Servo to all of a sudden start working.

[Squiggle Dog]

Those servos are possessed. Who knows? I'm glad I'm converting my car to manual climate control. That's great that you got your thermostat housing taken care of.

[tapavant]

I know this is an old thread but I feel like maybe someone in this thread knows the answer to this:



what does the thermo-valve actually do? Can it be safely disconnected? What is the point? Mine has the small black nipple broken off and I've plugged the vacuum lines that would normally lead to the thermo-valve but I'm wondering if I should try and purchase a new one and reconnect them.



Thanks in advance.

[Squiggle Dog]

I think the thermovalve just lowers the idle of the engine once it's warmed up, therefore reducing emissions or something. I think it's safe to disconnect as long as you plug the feed line so there is no vacuum leak, and then you may have to adjust the idle speed slightly.

[Diesel911]

Originally Posted by xaliscomex

Own a 1979 300sd (w116).

The thermostat housing (6172002415) is pitted/corroded at the inlets/outlets.
Although the rubber hoses are properly secured and tightened using good clamps, coolant continues to leak out.

I drained the coolant and replaced all coolant hoses approximately 6 months ago and I was surprised to see encrusted buildup at joints between the hoses and the metal openings (inlets/outlets) to the thermostat housing. Obviously, the buildup throughout the years is responsible for such corrosion/pits.

I thought about using some type of epoxy to smooth out the pits and even out the corrosion so that the hoses can get a tight fit but I wanted to know if anyone out there has encountered this problem before and what is the best way to handle this.

Before I go out and by a brand new thermostat housing, is there a better way to smooth out the pits or a better way to secure the hoses so that future coolant leaks can be prevented.

Also was wondering if I should use a silicone piece of hose (42mm) instead of a rubber hose between the thermostat housing and the metal line located directly under. Thats the area where I'm getting most of the coolant leaks. Hope I'm describing the area correctly. A short rubber hose (42mm) secured with two clamps on each end allows the coolant to flow thru.

Any advice is greatly appreciated

This as long as there is no large hole through it.
I have not read the other posts so this could be a repeat. I had the same issue on the Bypass Hose nipples as well as the upper Radiator Hose to Thermostat Housing. I cleaned out all of the white corrosion down to the bare metal.
I filled it with the slow curing JB-Weld Epoxy and quickly wrapped Masking tape around it. When I removed the tape I filled any voids and taped it a gain.
After that I filed and sand papered it back to the original contour and it has worked fine since about 2008.


However, I had other cars to drive while I did that.