Tackling Overheating - Part Numbers Request

[avantbenz]

I'm dealing with issues that are probably familiar to some of you out there.

My 1980 300SD is running hot (hottest she's been is about 105 celsius which is way too hot) and I'm trying to get her to run cooler. She doesn't run this hot all the time but if I'm on the freeway it doesn't take her long to reach 95 and steadily climb from there. She's my daily driver so I've been trying to take it easy, drive her slow, and limit my driving until I get this under control and if she ever runs too hot immediately pull over to let her cool down.

I purchased a new thermostat and when I went to take off the thermostat housing cover one of the bolts broke - surprise, surprise. It's in a very inconvenient place to try and drill the broken bolt out and I've read advice somewhere on the interwebs which suggests to simply purchase a new one rather than try and drill out a broken stainless steel bolt from aluminum housing.

So, now I'm looking for a new t-stat cover. While I was in there I also noticed two more things that need replacing that didn't a few days ago - my coolant expansion tank developed a pinprick leak on the side seam that I heard hissing and bubbling when I opened my hood this afternoon. I'll order a new one tonight. Also, the small hose leading from the radiator to the expansion tank developed a small tear and I need to replace that.

I need help finding / verifying the correct part numbers for:

1. The thermostat housing. I did a forum search and found this but I'm not sure it's the correct one for my car - mine seems to have a valve out the side of it - not sure what that does. Part number I found is: 1102030574 ( https://www.eeuroparts.com/Parts/404880/Engine-Coolant-Thermostat-Housing-Cover-1102030574/ ) Below is a picture of my thermostat with the unfortunate broken bolt. Has anyone successfully fixed this without purchasing a new t-stat cover? I just moved and money is tight so the less I need to buy right now the better. I could probably borrow some tools if I had a shot at making the old one work but if it's too long a shot I'll take the financial hit.
2. The small hose running between the expansion tank and the radiator itself. Picture also below.

Link to pics: https://imgur.com/gallery/3n16lxA

I hope these actions fix the overheating problem. If not I'll test for proper water pump operation. I've also never seen my auxiliary fan kick on so I'll see about figuring out a way to test whether it's the switch or the fan itself and possibly upgrade. So much to do...and that's why her name is 'Patience.'

[rumb]

The broken bolt screws into the housing behind the cover, so just a new cover wont help.

just the cover is A6172031374  $100.

the complete thermo housing is A6172002415 which is $3oo from MB.
https://www.mboemparts.com/oem-parts/mercedes-benz-thermostat-6172002415

the above parts are for engine number after 067786

you should be able to find this part at a wrecker I would think.

If you are handy with tools you could remove the thermo assy and take to a shop that can then easily and inexpensively remove the broken bolt.

you would also need A6162030280 gasket and the hose below is N900271042012 but is $100 for a meter, you can probably find something at the part store the same size if you need some.


The hose to the tank is just bulk hose.

the  crack in the tank and hose could be the reason for your overheating as the pressure is lower.

[rumb]

here is a less expensive option

https://www.ebay.com/itm/Engine-Coolant-Thermostat-Housing-Assembly-MTC-3829-fits-77-83-Mercedes-240D/132665045807?fits=Make%3AMercedes-Benz%7CModel%3A300SD&epid=243830387&hash=item1ee373f32f:g:rEEAAOSwPN9bIeQT&vxp=mtr

[avantbenz]

Rump, you're a lifesaver.

That ebay part looks like exactly what I'm looking for and is a lot cheaper than $300.

I found a mechanic that said he thinks he could probably drill the bolt out and preserve the threads. I'm going to take the entire thermostat housing out on Saturday morning (after letting her cool off after my Friday afternoon commute) and then Uber out to the mechanic and see what he can do. If he's unable to drill it out, then it looks like I'll be on ebay...

I might go ahead and test the water pump on Saturday morning as well. I would do it this afternoon but it's currenlty 104 degrees and I feel half dead in the heat. I'll update with my findings. I'll perform a search on how to best remove the entire thermostat housing. I imagine hose picks would come in handy and I'm open to any other advice.

Thanks again.

[avantbenz]

Update: got the bolt drilled out with threading intact! It was such a pain getting the housing out but I managed. Pictures and hopefully a tutorial to follow so people can see how I did it.

Now I'm missing a bolt - does anyone know where I can find a replacement?

Also, the part number for the short hose directly underneath the thermostat housing? Mine seems nearly completely deteriorated on the inside - it's practically gummy and upon reassembly began to leak badly.

[rumb]

twas posted already

hose below is N900271042012 but is $100 for a meter, you can probably find something at the part store the same size if you need some.

what is the bolt dimension I have many spare bolts, or you can probably buy one from MB, or perhaps your local hardware store.

[Squiggle Dog]

I got a genuine Mercedes N900271042012 hose from https://www.eurotruck-importers.com/index.php?main_page=product_info&products_id=622 for $7.15 plus shipping.

[avantbenz]

Rump, oops. Missed that. Shouldn't have posted while tired after a long day under the hood.

So, I managed to find the short water hose - genuine MBZ - via a local mechanic who *also* helped me plug up my new coolant expansion tank. I ordered one from pelican parts and was dismayed to see she had an extra hole in the side. I thought I'd ordered the wrong part but I guess that's how all the new ones come. The extra hole is for a different models sensor. There is, however, an expansion plug kit for the hole if your car is like mine. Order it when you order the tank to save time.

I still need to find a bolt that fits the t-stat housing cover. Rump, I'm not sure of the size - I'll have to take it out again to find out. When I do I'll let you know. It seems to be holding fine with no leaks with only two bolts.

I replaced the paper gasket between the thermostat housing and the block - I tore up my knife pretty good trying to get the old gasket off.

After getting everything set up with a new thermostat and gasket, blue coolant, and finding a hill to burp the system she's still running at about 90 so I guess the next step is to check the auxiliary water pump. I haven't even tested her on the freeway or going up a hill - that 90 is just from driving city streets a few miles during 70 degree weather. I also noticed that the evil servo is leaking coolant so maybe that's enough to cause a pressure loss and overheating? How can I fix that without fixing the whole servo system? I see a lot of forum searching in my near future. :-)

I'll post pics soon - too much of a pain on mobile.

[avantbenz]

Sigh. I wrote an entire reply complete with pictures and the focum logged me out as I went to post it. I'll try to re-create it...so frustrating. It probably won't be as detailed.

One of the pics shows the MBZ coolant expansion tank with the plug-kit installed. I originally just ordered the tank and thought it was the wrong part (Part #: 126-500-15-49-M22) but it isn't - you just need to the plug-kit in addition to the tank. They no longer make the same kind that was in the car (to my knowledge). 

Next pic shows what the thermostat housing looks like with the cover removed. It was hard to get the thermostat housing out due to limited space from the EGR and the heat shield. I was worried I'd have to take off the EGR valve to get the long bolts holding the housing in place but instead all I had to do was remove the top fastener from the heat shield to achieve more wiggle room. Voila!

Next couple pics are related to my questions. I've never heard my aux fan switch on even when I've climbed up to 105 celsius. I think it might be a faulty switch or it could be that the wiring is exposed. Does anyone have any suggestions for fixing this wiring? Or a part number so I can replace it? I'm not sure where the switch goes to and if it's an easy switch-out part so any advice you have will be well received.

Lastly, when I got the thermostat housing back from the mechanic it was missing the two rubber (I think) vacuum line connectors. Where can I get new ones and what is the part number, if any? Also, what do these do?

Thank you everyone for your continued help. I seriously appreciate it.

[Alec300SD]

It is annoying when you get timed out and lose your work.
I tend to now compose posts on a word processing program, and then polish the look with the preview option to avoid losing the work.

If coolant is leaking from the evil servo (or anywhere else), you won't be able to maintain a pressurized cooling system and the the car will overheat more easily.
Fix any leaks and test with a pressure tester at the new expansion tank.
Many auto parts store have tool lending programs, so you don't need to buy an infrequently used tool.


The auxiliary fan (for the A/C condenser) is switched on when the resistance in the sensor drops beyond a certain point.
The resistance drops as the temperature climbs.
Your sensor on the thermostat housing looks original and the internal resistance is probably out of spec.

Just ground the sensor wire to the engine (valve cover, etc.)  with a paper clip while the car is running.
If the circuit  is good the auxiliary fan will run.

If the fan doesn't run, then you have a wiring problem.
If the fan does run, then you have a bad sensor or a poor connection at the sensor.

[avantbenz]

Alec300SD, thanks for the response and good idea on composing out of the forum - I'll do that from now on for longer posts.

I'll rent a pressure tester from AutoZone soon because I think that'll be a good step towards fixing this issue. I've been reading through the massive "Still overheating" thread and picked up a lot of good information - https://forum.w116.org/mechanicals/still-overheating-(grrrrr!)/15/

I'll test the aux fan connection tomorrow. Question though and it's surely a noob one at that...when you say "ground the sensor wire to the engine" what exactly do you mean? Like, take it off and place it on the valve cover or somewhere else while the car is running? Where does the paper clip go? Thanks for walking me through this.

My servo is definitely cracked and I don't have the cash on hand to upgrade it to a modern solution. I found something in the ballpark of around $500 which I'm saving for but I'm not there just yet. Say it's the cracked servo which is causing a pressure loss that is causing me to overheat - how can I do a temporary patch-up to fix this until I can afford the modern climate-control solution? Or is it just something I have to live with until I can upgrade? I haven't taken the servo out to look at it but if I discover a crack could I try and mend it with jbweld or something with the intention of simply restoring pressure to my cooling system?

[Squiggle Dog]

I found that my auxiliary fan would never come on, even if I grounded the coolant temperature switch plug to the negative terminal on the battery (but the engine block or body would also work if you have a clean, unpainted surface). It turned out I had a bad relay cube. The auxiliary fan relay is located behind the vertical panel that goes by your left foot. There will be three of the cube relays on a 300SD. I think the one for the auxiliary fan is the one in the middle (I believe the top one is for power windows, and the bottom one is for the starter and climate control). If you don't have a spare relay, you can swap the three around and see if that makes the fan come on.

[Alec300SD]

The thermostat sensor completes the circuit to ground when it is hot,  and the resistance drops to almost zero.

You bypass the sensor when you complete the circuit to ground by inserting a conductor (paper clip, bolt, etc.)
into the female unplugged wire connector and then touch the conductor (paper clip, bolt, etc.) to an exposed metal surface connected to ground, (valve cover, thermostat housing etc.).

Remember that the auxiliary fan does not really aid much in cooling the engine, it mainly is there to help cool the A/C condenser tubes.

I have a used aluminum bodied servo from PNP that I was going to install in 'Stormcloud' .
This was before I bought a climate control upgrade kit from Blue300SD that I still need to install in 'Stormcloud'.
Send me a PM if you are interested in getting the used servo.

https://forum.w116.org/mechanicals/1st-gen-mercedes-accii-climate-control-servo-less-expensive-replacement-option/

Alternatively, you can temporarily bypass the servo by running a 6 foot loop of heater hose directly from the heater hose nipple (coming off the rear DS of the engine) to the return nipple on the water pump housing.
Note:  this will bypass the heater core, so you will loose the extra cooling capacity the heater core can provide if the engine begins to overheat.

JB Weld might work to effect a temporary repair to the housing, depending on where the leak is located.

[avantbenz]

The thermostat sensor completes the circuit to ground when it is hot,  and the resistance drops to almost zero.

You bypass the sensor when you complete the circuit to ground by inserting a conductor (paper clip, bolt, etc.)
into the female unplugged wire connector and then touch the conductor (paper clip, bolt, etc.) to an exposed metal surface connected to ground, (valve cover, thermostat housing etc.).

Remember that the auxiliary fan does not really aid much in cooling the engine, it mainly is there to help cool the A/C condenser tubes.

I have a used aluminum bodied servo from PNP that I was going to install in 'Stormcloud' .
This was before I bought a climate control upgrade kit from Blue300SD that I still need to install in 'Stormcloud'.
Send me a PM if you are interested in getting the used servo.

https://forum.w116.org/mechanicals/1st-gen-mercedes-accii-climate-control-servo-less-expensive-replacement-option/

Alternatively, you can temporarily bypass the servo by running a 6 foot loop of heater hose directly from the heater hose nipple (coming off the rear DS of the engine) to the return nipple on the water pump housing.
Note:  this will bypass the heater core, so you will loose the extra cooling capacity the heater core can provide if the engine begins to overheat.

JB Weld might work to effect a temporary repair to the housing, depending on where the leak is located.

Alec300SD, thank you for the offer. I think I'm going to take a leap of faith and buy what I think is the same system that you're planning to install in Stormcloud. I'll pull the trigger within the next few days - I think JBWeld is going to be too much of a hassle and probably won't work and I want to nip this in the bud.

I'll update when I have more to report.