Thermo Time Switch

[specracer]

Forgive me if this has been discussed in great detail, but using the search provided limited info.

My thermo time switch is no good (prior owner installed a push button for the cold start fuel injector).

Looking at replacement options. This is not a concourse car, never will be, so we can ignore the $800+ NOS options I don't mind the connectors, vs screws.

the 2 options I'm looking at, are both on ebay. Option 1 is Buds at $285, this is of course a great option, as Bud's is a "tier one" MB supplier.

The other is a "rebuilt option" that is $149.50 "rebuilt by a Mercedes mechanic" Is this provided by anyone that has an affiliation with this forum? Anyone have any thoughts on this?

Note, I'm good with either price, and my gut tells me to go with the new part, but curious what others think.

[Pawel66]

Best of my knowlegde:

1. Bosch option (discussed on the forum)
2. MB option (discussed on the forum - can be the same as Bud's or authentic classic, just cheaper from Mercedes - check it! - it was the case in my geography)

I have Bosch in the car - works very well.
http://www.bosch-classic.com/en/internet/bosch_classic/produkte/motor_1/thermozeitschalter/thermozeitschalter___mit_teaser_1.html
F 026 T03 101. 12V/35deg C/12Sec (yes, you need it at 35deg)
1 284 485 110 plug Bosch number
MB A003 545 0226 the terminals.
https://www.sl113.org/forums/index.php?topic=26041.msg186581#msg186581


This is Mercedes recommended, costs about $100 (but I have not used it):

A 001 545 92 24 (original TTS, now rebuilt by Classic Center for $600) to replace with:

A   004 545 91 24 x 1 - which is a thermo switch
A   009 545 44 28 x 1 - which is pin bushing housing
A   003 545 26 26 x 2 - these are pins
A   009 545 45 28 x 1 - this is cover for this housing

This one, I think, not sure though, is offered by internet stores, but I found it was cheaper in MB.

I found this as well (the original TTS was a VDO unit): VDO 232-036-002-009D, but I have never found this part.

[mazmonza]

This is what I have used if it helps.  About £70

Maurice

[Shvegel]

I found a picture of the later Bosch unit showing 9.5 seconds @20 degrees C.  I think the original is pretty close to that.

Before anyone condemns one of these wildy expensive little devices please make sure you or your mechanic has a through understanding of how it works. The thermo time switch does not supply power (battery +) to the cold start valve.  power is supplied via another circuit.  What the thermo-time switch does is supply a ground (battery -) to the cold start switch for a few seconds based on a sliding scale that is dependant upon temperature.  There are 2 terminals on the switch.  One is connected to a small heating element that gets it's ground from the cylinder head and the other is connected to a thermal switch that is also connected to the cylinder head.  no separate connections they are just connected to the brass housing internally.  When the engine starter is engaged power is fed to the heating element which heats the thermal switch and causes it to open disconnecting the ground circuit from the cold start injector. 

All of this is fairly easy to diagnose.  What you have is essentially 2 circuits here with each running between the wiring terminal and ground.  The terminal are stamped "G" and "W" near the screws.  Measure resistance between the "G" terminal (small screw) and the brass body and you should have about 50 ohms of resistance at all times warm or cold.  Now for the tricky part.  With the engine at room temperature {20 degrees C or 68 degrees F) connect a volt meter set to volts DC between the "W" terminal and the brass body.  Remove the coil wire from the ignition coil and have someone turn the key to start  and watch the meter.  You should see less than half of one volt for 8 or 9 seconds and then the meter should jump up to 11 volts or so.  If you see more than half a volt it means the contacts in the thermal switch are bad and if you don't see a jump in the 8 to 9 second range it means the contacts are not opening due to there either being no power applied to the "G" terminal during cranking or there being no power applied to the cold start valve.

The last test I outlined is what is called a voltage drop test.  It is a little more accurate than just measuring the resistance between the "W" terminal and the housing because it is testing the contacts in the switch with power flowing through the contacts.

[Pawel66]

As amateur with limited skills and having gone through struggle with the TTS I can only confirm: to me the way this system works was neither obvious nor intuitive. And yes, before spending $$$ it is good to have it diagnosed properly. And in order to do that you have to understand it.

As for the choices, I reflected a bit on that... If I were after purity, I would go for Tom and Classic Center solution. I failed to determine if this solution is available in CC in Europe.

If I were after just functionality or if there are limits on the $$ you want to spend, I went for the Bosch solution. If the MB proposed replacement was known to me at that time, I would have considered that as well. I do not know, however, how it works when you install it.

I found two VDO part numbers for the Mercedes proposed replacement (A004 545 91 24): 232-036-002-019D and 232-036-002-020D.

[Shvegel]

Pawel,
I too struggled with thermo time switches back in the 70’s when I started working on European cars.  I called quite a few of them bad thinking that it was a switch between the two terminals before I really studied some wiring diagrams and figured out how they worked.

[Pawel66]

Well, for me the process was fast becuase it was you guys, who explained it!

[ja17]

Do not confuse the "thermo switch" with the "thermo time switch". The "thermo switch" is only an on/off temperature switch. The "thermo time switch" is an on/off temperature switch with the added time duration function. Only the early pagoda cars (starting aids version II and version III) have the "thermo switch". The most common (version IV) have only the "thermo time switch" (tts). The thermo time switch supplies or interrupts the ground to the starting aid solenoids. These solenoids in turn supply or interrupt power to the starting aids themselves. The starting aids themselves have continuous ground.

[wwheeler]

Joe has a good point. From what I understand, the thermo switch is NLA at any cost. Probably can get a used working one since these were just a simple switch.

BTW, you might want to keep your cabin CSV switch. Many people have installed those (including me) to fire fuel into the manifold before the engine starts. Works everytime and you can eliminate the starting solenoid if equipped.

Don't make the assumption that because there is a switch in the cabin, that the Thermo-time switch doesn't work. Many people added those as I mentioned.

[A Dalton]

Joe has a good point. From what I understand, the thermo switch is NLA at any cost. Probably can get a used working one since these were just a simple switch.

BTW, you might want to keep your cabin CSV switch. Many people have installed those (including me) to fire fuel into the manifold before the engine starts. Works everytime and you can eliminate the starting solenoid if equipped.

Don't make the assumption that because there is a switch in the cabin, that the Thermo-time switch doesn't work. Many people added those as I mentioned.

Exactly
 The manual cabin is simply an add-0n circuit..meaning it over-rides the TTS/Starter circuits b/c it is wired in parellel .

 If it is not used ,the start circuits are  still factory wired as if there is no mod.
But b/c you can now over-ride the factory circuits, you have a better starting car, specially where we wire them for squirt from CSV BEFORE starter engagement.  THAT is the trick that none of the  four modified factory start circuits ever had.
 A simple , best bang for the buck winner as far a starts are concerned.

[specracer]

WOW this is fantastic information. Thank you

It has been at least a month since I looked at it, so I don't remember all the details, but what I did was test continuity to ground of the thermo time switch. I would expect, I would see ground until the time expires, then the ground is broken. I have no ground ever. And this is a thermo time switch as this is a 1970 280.

[Pawel66]

If start is ok when you connect ground through a jumper wire or through the switch to the relay connector - it may be the TTS. You have the options below.
I have read that since these Mercedes cold start systems of the 60ies never, really, were absolutely and definitely finally perfected , I think it is a good piece of advise to leave that switch there.

In my case - I had cold and warm start problems. I looked into Technical Manual, fellow Members explained to me how it works. I did not find ground on W. I replaced the TTS with the Bosch unit. Now she starts when she sees me walking up with the key in my hand - cold and warm.

[wwheeler]

My biggest mistake in using the CSV switch prior to starting the engine, was that I did not activate it long enough. Now I typically hold it in for 2 to 3 seconds for a cold start. The reason for the longer time is simply because you are not injecting the fuel directly at the cylinder. Rather it squirts inside the intake waiting for air to mix with the fuel vapors and then into the cylinder.

In my opinion, it also helps to hold the throttle half open in order for air to wash over and pick up the fuel vapors. If the venturi is closed, the air will mostly come from the idle screw circuit which is farther ahead of where the fuel in the manifold is. Plus air coming from the venturi will create more turbulence and therefore creating a better air/fuel mix for starting. And yes since I have the CSV switch, I have never had to use the starting solenoid under any condition. For me, the starting solenoid causes more issues than it helps.   

I believe this was mentioned previously, but there is also a good write up about testing the TTS. - https://www.sl113.org/wiki/Engine/ThermoTimeSwitch
With this, you should be able to definitively test the device.

[specracer]

The testing procedure in the tech manual is exactly what I used to diagnose the TTS, as well as understand how it works. This site is such a great resource!

[Shvegel]

JA17,  Thanks for the clarification.  Since most of my experience with thermal time switches is based on 1970's cars I did want to check myself and went to the diagrams in the members only area.  Unfortunately withut a legend I wasn't able to pick out the cold start system.  I try to always check myself and I hoped if I made a mistake that you or Dan would speak up.  Thanks again.

[ja17]

Shvegel, thank you for all your exceptional contributions. I have learned a lot from you. I too am corrected and enlightened from time to time. Its all part of the process of learning as you know, and we are all among friends here!

[Tyler S]

Just an FYI for everyone. A Porsche thermal time switch part #91161711700 is an almost identical part as the NLA MB part. It was used on the Porsche/Bosch MFI systems which are almost identical to ours in function. They were also used on porsche CIS systems. You will need to remove the threaded electrical studs from the porsche part and transfer the eyelet retainers from your old switch. There is a 15 degree difference in the upper cutoff so will not cutoff untill a bit higher temp. Cosmetically it is identical. I Have one in my car. Works great. Link below for reference but they are also available elsewhere.

https://www.pelicanparts.com/More_Info/91161711700.htm?pn=911-617-117-00-M100

[Shvegel]

Tyler,
Thanks for that.  I bought one just to have it on a shelf in case my current one is bad.  When they have to make a new run they will be $1000.  Pelican's price looks to be the cheapest.

[wwheeler]

Yeah Tyler! Thanks and I just got an extra for my W128.

[Pawel66]

Tis looks like a winning option, actually!

[specracer]

In trying to order these parts from MB, been told that these parts are the dreaded NLA. The thermo time switch it self is coming from Germany.

009 545 45 28 x 1 - this is cover for this housing
009 545 44 28 x 1 - which is pin bushing housing

A   004 545 91 24 x 1 - which is a thermo switch
A   009 545 44 28 x 1 - which is pin bushing housing
A   003 545 26 26 x 2 - these are pins
A   009 545 45 28 x 1 - this is cover for this housing

[teahead]

Just an FYI for everyone. A Porsche thermal time switch part #91161711700 is an almost identical part as the NLA MB part. It was used on the Porsche/Bosch MFI systems which are almost identical to ours in function. They were also used on porsche CIS systems. You will need to remove the threaded electrical studs from the porsche part and transfer the eyelet retainers from your old switch. There is a 15 degree difference in the upper cutoff so will not cutoff untill a bit higher temp. Cosmetically it is identical. I Have one in my car. Works great. Link below for reference but they are also available elsewhere.

https://www.pelicanparts.com/More_Info/91161711700.htm?pn=911-617-117-00-M100

Can you confirm the one below is what you have?  The pelican link points to a newer one that doesn't quite look like the one you referenced.

I.e. 91161711700  looks like this:



91161711701 looks like this:

[teahead]

45 deg. C.

Too warm?

[Shvegel]

I can see what happened.  The finally ran out of the original design and had to make a new run.  Surprisingly, they are not $1000.  The drawback I see in the 01 switch is it looks like the terminals are not removable as they are in 00 switch.  I can't imagine the extra 10 degrees of operation would effect it much bearing in mind the heating element is energized with every start.  I am sure the operating time at over 35 degrees is in the fraction of a second range.

[Shvegel]

For what it is worth I also think this switch would work really well.  Same spec as ours.  As an added bonus it has circuity that gives the cold start injector a 1 second shot even when warm which Mercedes tried to do in a later retrofit kit for the 280SLs. The electrical connector is a standard Bosch 2 pin EV1 terminal connector that is easy to find and much more waterproof than the original.

Specs here (The dash 100 switch under "Part Numbers" is correct):
http://www.bosch-classic.com/en/internet/bosch_classic/produkte/motor_1/thermozeitschalter/thermozeitschalter___mit_teaser_1.html

Here is an Amazon link:
https://www.amazon.com/BOSCH-Temperature-Sensor-Switch-F026T03100/dp/B00YCI8PVC

Connector:
https://www.amazon.com/Injector-Connector-Waterproof-Connectors-Harness/dp/B07C7QSQBY/ref=sxbs_sxwds-stvp?keywords=Bosch+EV1+pin+connector&pd_rd_i=B07C7QSQBY&pd_rd_r=4e1255a7-08ae-4307-ae68-98a0b601623f&pd_rd_w=mno7p&pd_rd_wg=F48iv&pf_rd_p=a6d018ad-f20b-46c9-8920-433972c7d9b7&pf_rd_r=P2KSRA6R9EK5VVQA44DF&qid=1565542676&s=automotive