Mercedes Engine Overheating Protection R129, R107, W124, W140, W201 Coolant Temperature Sensor Trick
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- Опубликовано: 9 мар 2024
- How to replace your Benz coolant temperature sensor responsible for ensuring your car never overheats to the point that it can cause serious damage to your engine and head gasket. Video also covers a very common hack to trick your car into turning on the aux fans at a lower temperature. In doing, it keeps the engine temperature within a smaller range of acceptable temperatures.
The video was shot in March and the temperature was barely above freezing, so I could not get a chance to test the sensor and its modification. I will periodically post updates here. My car did not need the resistor hack, but I did it so I could share this knowledge and how-to via RUclips with the R129 global community. As always, I'm happy to share as much as I can with you.
Update: May 20 - Finally, very warm weather. The outside temperature was 30 Celsius (86 Fahrenheit) and the high speed aux fans kicked in a bit over 95C (reading from the instrument cluster). That's success.
Video applicable to most R129 SL, including the 500SL, 300SL, 320, most W124, W140, W201 and for many other 1980s and 1990s Mercedes-Benz, including those with KE-Jetronic.
ECT sensor (auxiliary fans) - air conditioning and extreme overheating protection (B10/8).
ECT part number: 008 542 4517 (Always check with your parts supplier for exact part for your make and model). Test your old sensor before buying.
Torque Specs: 25 NM
Sensor used in video: NTK (Made in Italy). Mercedes still makes it. Hella is also an excellent choice.
Resistor: 1000 Ohm, 1%, 1/4 Watt (Turns fans on at at about 90C)
Resistor: 1200 Ohm 1%, 1/4 Watt (Turns fans on at about 95C)
Note: Blue resistors usually heat resistant and better suited for engine bays, than other colors.
Note: Resistors can be soldered into place, once the desired resistor is found
Location of parts shown in the video will vary by model and year of car, but they are there.
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Car Shown: 1992 Mercedes-Benz 300SL (M104.980)
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Please see my Handy Val channel for my many Mercedes How-To videos on a number of different topics, and don't forget to like and subscribe as I post new videos regularly.
Disclaimer - The content of this video is available for informational and educational purposes only. It is not intended to be a substitute for professional advice. I do my best to provide accurate and complete information, however, I assume no liability for any property or personal damage that may arise from any of the information contained in this video. Due to factors beyond the control of Handy Val, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Handy Val always recommends safe practices. 
Хобби
Thank you!! My part just arrived! I’ll do tomorrow morning!
Many thanks. Always appreciate your help and advice
My pleasure! I'm really passionate about sharing this topic.
Thanks Val great stuff! I purchased a pre made resistor in a cap that fits on the prongs then the wiring fits in to the cap. 100 bucks..... now the fans come on at about 90 c with or with out the air on I love it works grate especially for me as I live in the desert where avg summer temps are 115-118 not much fun to drive in those temps.
Thanks for sharing. You definitely need the resistor. It’s a smart choice to go with the pre-made resistor - it makes it easier…plug and play. Your engine is thanking you for every single one of your summer time drives.
Thank you Val - was up early enough to catch you first inline. I really learned more about this sensor. And have never given it a second thought - NOW I HAVE! Since my R129 is already in the shop I’ll have them check it out for sure. By the way - again - an AWESOME Instructional video. Mark🙏
Thanks Mark. I appreciate it. This sensor is so critical to the long-term well being of an engine. I want to ensure every R129 has a proper working sensor. Its function is basic, yet so important. They are cheap, easy to replace and simple to test.
@@HandyVal bless you Val - thank you 😊
Did it work, did the auxiliary fans kicked in at 90 degrees?
The temperature here is still a few degrees above freezing. I tried but it wasn’t warm. The cool temperature kept the engine cool without further assistance. I will provide updates in the video description later in April hopefully when the weather is much warmer.
Great video. I am worried about how hot my benz 300e is getting. I will check some things you mentioned. Good quality vid also!
Thank you. Keep me updated. How hot does it get?
Good stuff VAL 😇😎
Many thanks. 🙏 Overheating is such a critical topic for many R129 owners. I was happy to put as much as I know of this topic into this video and some of the other videos I made too, like those on the coolant system.
Hi Val, Do you know what the other Temp Gauge is for that is just the right of the one you replaced? Many thanks for all of your videos.
Thanks. The sensor to the right is also a coolant temperature sensor and it only leads to the instrument cluster temperature gauge. The reading from the instrument cluster comes from it. I hope this helps.
Great content
Many thanks. Always appreciated.
@@HandyVal@HandyVal Because of YT channels like this, I just purchased an SL320 yesterday. It's a late 95 with a full-service history and lots of mint-condition documentation, a new hood, and a new hood control unit.
@@ministryofengineering3850 Thank you. I try to make these videos as best as I can. It looks like you purchased a solid R129. History is the most important. It helps to know what has been done and when something needs to be done.
When you add resistor to coolant sensor, does it change the temperature reading on speedometer cluster, what you see behind the steering wheel? Or other sensors provide that information?
The resistor trick on the blue sensor only impacts the engine overheating protection via the high speed aux fans. It has no impact on the instrument cluster reading. The instrument cluster reading has its own sensor. No other sensor readings are impacted.
Great video. Went to check mine and the connector was so brittle it fell apart. Do you have the part number for it?
Thank you. The connector part number is 001 545 7128.
Awesome!
Val do you have information on replacing engine oil pump on R129 300SL 1991
Hi. I don’t have any good knowledge or experience to share with the engine oil pump. I assume you’re getting low oil pressure? Sometimes it could be as simple as a clogged or cheap oil filter causing those symptoms. Start there. From what I know, it’s an involved process as you need to get the car on a lift, remove the oil pan and then you’ll have access to it. There’s also a chain. There are a few steps. Sorry, I can’t be of more help.
hello, on a mercedes w140 s350, I'm thinking of installing the resistor, I guess there won't be a problem
Yes. It should work just the same. I believe the S350 has the same Blue sensor (B10/8) as shown in the video. If it does then go ahead and try it out. Keep me updated.
Hello Handy,
I need your knowledge to help me on the following issue that I have on my MB SL 320 1995......114K Miles.
I am getting the following OBD2 code ..... (CEL) P-0400..Current....'Exhaust Gas Recirculation Flow'. I am using the icarsoft scanner. The CEL appears at abour 2000 RPM while driving. Also, we have replaced the Engine wiring harness. As you are aware, that these model had issue with the wiring harness insulation breaking off.
I have already done the following:
1-Replaced the EGR valve with an OEM part
2-Replaced all the vacuum lines flexible tubes and plastic ones.
3-Checked the Vacuum solenoid. There is perfect vacuum at the Soleoid from the THrottle body. The solenoids for EGR and the Seconday Air Compressor click when I appply 12V on each of the terminals.
4-Cleaned EGR line. Checked with the compressed air. There is no resistance to the flow of air.
5-Checked the EGR by sucking in. It opens.
5-Replaced the Engine Coolant Thermostat. It was found disconnected at one of the holdind clips.
6-The connection at the single wire ECT (Engine Coolant Temperature) that indicates temperature on the dashboard was found found disconnected. Re-soldered it and the now the coolant temperature is showing around 80C at the dashboard.
7-I don't want to touch the ECM.
What else do I need to do to reset this code for good ?
Regards,
Syed
Syed, you’ve done everything right. The P0400 code is usually a bad EGR, which you’ve replaced, or a vacuum leak, which you’ve checked. What exactly happens at 2000 RPMs? Is it only a CEL, or do you have driveability problem?
I don’t think it’s the ECU. If it was the ECU you’d have other problems. The ECU works with the EGR and the MAF to control air flow. So if everything around the EGR is good, then it could be the MAF sensor. Try cleaning the sensor with a MAF sensor cleaner. I hope this helps.
Sir,
I was able to get rid of the the P-0400 by replacing the Positive crankcase pressure gaskets and two rubber pipes on the engine. My new issue is very simple. I am getting the new OBD11 code P-0441(Evaporative system issue). I have changed the fuel tank cap. The problem now is that the tube connecting the evaporative solenoid output tube got disconnected from the engine. Can you please let me know the point on the engine where this tube needs to be connected ? A picture of the connecting point on the engine will help me.
Regards,
Syed
@@syedshahid492 Congrats on fixing the P0400. The 320 was an early adopter of OBDII, so it's great to read such detailed codes. I did check my files, and I'm not able to find what you are looking for, and I searched a lot - sorry. I suggest you try the 'old fashioned' way with a mirror looking for the connection point. It's a pain but with some patience you'll find it. Sorry, I couldn't help more.