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

[teahead]

Well...I installed the new TTS and still, no power going to the cold start valve (CSV) while cranking.


Guess I gotta do more testing.

[jpringot]

Hello
In this thermo swich on ebay with connector
where is the w and the g? or on the connector ev1 red or black ?

[teahead]

Hello
In this thermo swich on ebay with connector
where is the w and the g? or on the connector ev1 red or black ?

You're talking about the switch 91161711700?

It's labelled.  Can't miss it.  As aforementioned, you take off those pegs that are on there and install the screw hole nuts.  Very easy.  W & G are labelled.

[Figoulu]

Hi gents

I'm having trouble with my TTS and puzzled about the prices of such a device

Searching on the net I found a possible part that could fit: https://vdo-webshop.nl/en/temperature-switches/825-vdo-temperature-switch-35c-m14-4103590689283.html
 
But as you may have seen only one connection is available while I have 2 cables
I was wondering wether the ground cannot be inserted between the washer and the thread ?
Would it work like that ?

Thanks !

[mnahon]

Hi Figoulu,

That switch is quite different in function. It will simply turn on or off at 35C.

The function of the TTS on our cars is more complicated. It's intended to energize the cold start valve for a duration of time. When the engine is cold, that duration is ~5-10 secs. The duration decreases as the coolant temperature increases. Eventually, at around 35C, the duration drops to zero.

You can find, in the technical manual, a more detailed description:
https://www.sl113.org/wiki/Restricted/Engine-starting-aid-tour

[Pawel66]

There were numerous threads about replacements of various types. Of course you can find original replacement, it will be horrifyingly expensive.

I used the modern Bosch Bosch replacement as shown on attachment. Part number will be e.g. F026 T030102. And connectors - at the bottom of the table.

[Figoulu]

Thanks Pawel
Still 130€ appeared high enough to find an alternative…
I understand it’s not really possible to spend less 😅

[Figoulu]

There were numerous threads about replacements of various types. Of course you can find original replacement, it will be horrifyingly expensive.

I used the modern Bosch Bosch replacement as shown on attachment. Part number will be e.g. F026 T030102. And connectors - at the bottom of the table.

Additionally Pawel, considering the small differences between 100, 101, and 102, can i freely go for one of these without any issues ?

[Pawel66]

I think indeed that it would be difficult to spend less...

They are the same in terms of dimensions. I do not remember which one I have, I think 102 and it works very well. It is important during hot start when you have your car tuned so that it does not run too rich, spark plugs being light tan. Then hot start may be an issue.

Just my opinion.

[Figoulu]

I think indeed that it would be difficult to spend less...

They are the same in terms of dimensions. I do not remember which one I have, I think 102 and it works very well. It is important during hot start when you have your car tuned so that it does not run too rich, spark plugs being light tan. Then hot start may be an issue.

Just my opinion.

Having read the starting aid topic, the right timing on my TTS is finally 9.5s
So 101 is the most accurate while the other ones are not totally out of the scope…

[Figoulu]

Found one on ebay

NOS for 110€ postage included…
Ref is 100 which apparently is equivalent to 102

[Pawel66]

Excellent!

I bought mine a couple of years ago form Bosch service nearby, just ordered via email.

[Figoulu]

Excellent!

I bought mine a couple of years ago form Bosch service nearby, just ordered via email.

I checked before all, but they are no more providing stocks on those refs

[Pawel66]

I checked before all, but they are no more providing stocks on those refs

I see, good to know...

[MarkCan]

It is with pleasure that I’m reading this thread. Finally something that I need for my rebuild is in the parts lot and appears to be in good working order. 👍

[Pawel66]

That is a money and trouble saver if so !

[Jean-Philippe Ringot]

Bonjour,

Je viens d'acheter le thermo time switch Réf.: F 026 T03 101 quelqu'un peut il me dire le branchement sur les cosses du fil rose/bleu et le fil rose ? Merci

[Peter van Es]

I have just bought the thermo time switch Ref.: F 026 T03 101 can someone tell me the connection to the terminals of the pink/blue wire and the pink wire? Thank you

Check this: https://www.sl113.org/wiki/Engine/ThermoTimeSwitch
Item 32 on the wiring diagram: https://www.sl113.org/wiki/Restricted/ColorWiringDiagrams
Pink (rose) goes to W
Pink/Blue goes to G

[Pawel66]

Bonjour,

Je viens d'acheter le thermo time switch Réf.: F 026 T03 101 quelqu'un peut il me dire le branchement sur les cosses du fil rose/bleu et le fil rose ? Merci

You have the drawing of the connectors of the new TTS in reply no. 31 in this thread.
Pink/blue to plus (G on the old TTs).
Pink to signal (switch symbol, W on the old TTS).

[Jean-Philippe Ringot]

Merci beaucoup ! J'ai pris le BOSCH F 026 T03 101 pour ma 280sl/8 1968 ! Ai je fais le bon choix pour ma pagode ? Merci

[mauro12]

Hi guys , just a quick word about this tts .
I was checking on eBay and the size seems to be higher and the probe smaller in size . There is no risk of touching the coolant pipe with the terminal connectors ? Can you post a picture of this sensor in your car ? Thank you

[mauro12]

Any help from somebody ? i guess this type of sensor is good but maybe some modifications are needed , like it seems to be much higher that the original and the wire connection is very close to the coolant pipe above . Any pictures ? thank you

[Figoulu]

Hi all

I'm about to plug my TTS but the electrical connector provided with the bosch part need to replug the original connector

Anybody knows the type of connector (Iso ?) that I need to purschase to match Bosch plug ?
Thanks

[BobH]

Hello, the part numbers for the connector are on this thread if you have a look back at earlier posts

There's a picture and instructions on here

https://www.sl113.org/wiki/Engine/ThermoTimeSwitch?action=download&upname=W113%20Cold%20Start%20Thermo%20Time%20Sensor%20Alternative%20rev%201.pdf

[Figoulu]

Hello, the part numbers for the connector are on this thread if you have a look back at earlier posts

There's a picture and instructions on here

https://www.sl113.org/wiki/Engine/ThermoTimeSwitch?action=download&upname=W113%20Cold%20Start%20Thermo%20Time%20Sensor%20Alternative%20rev%201.pdf

Ohhhh thanks and sorry 👍👍

[BobH]

No problem, good luck with the remainder of your restoration

Bob

[benzwallah]

Not sure if this is a thermo switch issue, but would welcome any thoughts:

This winter, it has taken me about 10-20 cranks to start my engine.  As temperatures rose in March, it took me about 5-7 cranks.  My mechanic looked it over and said the thermo switch was no longer working, but that with warmer ambient temperatures, the car (230SL 1965) should have less trouble starting.

Yesterday, it started on the first try.  Drove it several miles and stopped for an hour.  Tried to start it, but again it cranked for about 30 times.  Weather in the 60s.  Finally, as the battery was clearly starting to lose strength, the engine barely caught, and with some delicate footwork on the accelerator, I got it to start.  Back in the garage after driving 30+minuutes to replenish the battery, I tried another re-start after turning off the engine.  It cranked again 3-4 times but caught.

I am reluctant to take the car out again.  Any thoughts or recommendations welcome.  Do I need to replace the termo switch?  The mechanic (who is terrific) implied that in warmer weather, starting it up should not be a problem since the thermo switch is only needed in colder temps.

Thanks in advance for any advice. 

[rwmastel]

Benzwallah,

As a full member, you have access to the Tech Manual.  There is great detail there about starting aid systems.  There was also a very detailed thread a few months ago that you can search for.  Lots of replies in that thread.  When searching, just limit the days age of search results to 150 (default is 9999!) and that will help you find it.

Between that thread and the Tech Manual, you can educate yourself quite a bit.  That may be an understatement.  You can do some diagnosis yourself, or some repairs yourself, or just use your new found knowledge and tell the mechanic what to do.  It will impress him/her!

[Figoulu]

No problem, good luck with the remainder of your restoration

Bob

I finally went for “normal” connection as the iso connector hasn’t enough space with the curved hose…

[BobH]

Not sure if this is a thermo switch issue, but would welcome any thoughts:

This winter, it has taken me about 10-20 cranks to start my engine.  As temperatures rose in March, it took me about 5-7 cranks.  My mechanic looked it over and said the thermo switch was no longer working, but that with warmer ambient temperatures, the car (230SL 1965) should have less trouble starting.

Yesterday, it started on the first try.  Drove it several miles and stopped for an hour.  Tried to start it, but again it cranked for about 30 times.  Weather in the 60s.  Finally, as the battery was clearly starting to lose strength, the engine barely caught, and with some delicate footwork on the accelerator, I got it to start.  Back in the garage after driving 30+minuutes to replenish the battery, I tried another re-start after turning off the engine.  It cranked again 3-4 times but caught.

I am reluctant to take the car out again.  Any thoughts or recommendations welcome.  Do I need to replace the termo switch?  The mechanic (who is terrific) implied that in warmer weather, starting it up should not be a problem since the thermo switch is only needed in colder temps.

Thanks in advance for any advice.

Hello, there are some excellent write up's on here and in the tech manual, but it can be a bit overwhelming getting your head around how the cold start components work together.  Your mechanic says he suspects the thermo time switch (TTS) may be faulty, but has he diagnosed it?  there are several components involved, the TTS, the cold start relay, the cold start valve and some other bits.  The quickest way to rule out if the TTS is faulty is to temporarily apply an earth/ground wire directly to terminal W (where the pink wire is connected) and then crank the engine.  If it starts easily then the TTS may be at fault, but you'll then need to test it fully to make sure before you splash out on a replacement.  There are descriptions on how to test it on the various posts and in the tech manual.  In the meantime you can use the earth wire to start the car if that works, until you sort a permanent fix.  Some owners have wired a push button, as a manual "choke" to bypass the TTS.  If the earth wire doesn't work, there may be a problem with the relay or the cold start valve, (the solenoid or the spray nozzles), or the wiring in between.  Please let us know how you get on
Good luck