1984 500 SEC COOLANT TEMP SENSOR - PeachParts Mercedes-Benz Forum

Jitters · #1 03-09-2013, 01:14 AM

Hi,

New to the board. I have a 1984 500 SEC Euro and am trying desperately to find out if the car has a thermo time switch or a coolant temperature sensor or both. I also need to know where they are located on the engine...

Best Regards,

Todd

pmckechnie · #2 03-09-2013, 07:21 AM

It should have both. Standing in front of the car the coolant temperature is in the thermostat housing at the front of the engine. It should have a single green wire attached. The thermo time switch is to the right in the intake manifold very close to the front of the engine. It has 2 wires but I don't remember the colors.
I could be wrong on some of this as it is a EURO car.
Are you having a problem that we may help you with? These two sensors are not related except they monitor coolant temp for 2 different systems. One the gauge and the other for the cold start injector.

Paul

Jitters · #3 03-09-2013, 09:34 AM

Good Morning Paul and thanks for responding to my post. I'm actually researching a rich idle condition. My mechanic had mentioned that there possible could be an issue with the coolant temperature sensor. Apparently, he explained that the sensor feeds a signal to the ECU which in turn affects fuel delivery if not working correctly.

I ordered a temp sensor from PP's; however, I haven't been able to locate anything on the car that looks similar....I've found the Thermo Time Switch.

The temp sensor that I purchased has 2 leads so I don't believe this is for the gauge. My gauge works perfectly....

I've also noticed that the Economy gauge, at idle, is about 1/3 the distance from the far left. I'm assuming at idle, it should be pegged all the way to the left...

One last point. I've changed the dizi cap and rotor, got new plugs; however, the number 8 cylinder is not firing. If I pull the plug wire,there is no change in the engine....

Thanks again for the response.

Best Regards,

Todd

Jitters · #4 03-09-2013, 11:58 AM

Hey Paul,

Thanks again for the feedback. I was able to locate the coolant temp sensor this morning. If you're standing in front of the car, the sensor is located on the left rear side of the intake manifold.

Replaced it with a new one and there seems to be a little bit of difference in the idle but still not close to being perfect.

The car still seems to be running rich. There's a small amount of black smoke at idle when cold and if I accelerate the gas pedal aggressively, there is a lot of black smoke that comes from the exhaust.

Doesn't happen under normal driving conditions only when I punch the gas...

Looks like there's much more work to be done...:-)

Best Regards,

Todd

jimandsuzy · #5 03-09-2013, 12:13 PM

Is this a new symptom or is the car new to you? I bought a 500sec that had your symptom and just had to re-adjust the mixture to fix. No idea who did it or why it was out of adjustment but it's been fine now for about 3 years.

.

pmckechnie · #6 03-09-2013, 12:14 PM

Could you give me a little history on the car? How long have you had the car? How long have you had the running rich problem? Does it run rich when cold, warm, or both? What kind of plugs did you put in the car?
The low vacuum could be because of the #8 cly problem and/or a vacuum leak.
I don't think the Euro cars had an ECU. There is a 2 terminal coolant sensor in either the left or right rear of the engine but it disables the heater fan until coolant gets to 120(?) deg f. Even if it had an ECU it wouldn't have a temp sensor. The warm up mixture is done by the Warm up compensator or sometimes called a control pressure regulator. It is a small box about 2X3 with 2 fuel lines and 2 wires and maybe 1 or 2 vacuum lines. It is at the left front side of the engine looking at the engine from the front of the car.

Paul

Jitters · #7 03-09-2013, 01:38 PM

Quote:

Originally Posted by pmckechnie

Could you give me a little history on the car? How long have you had the car? How long have you had the running rich problem? Does it run rich when cold, warm, or both? What kind of plugs did you put in the car?
The low vacuum could be because of the #8 cly problem and/or a vacuum leak.
I don't think the Euro cars had an ECU. There is a 2 terminal coolant sensor in either the left or right rear of the engine but it disables the heater fan until coolant gets to 120(?) deg f. Even if it had an ECU it wouldn't have a temp sensor. The warm up mixture is done by the Warm up compensator or sometimes called a control pressure regulator. It is a small box about 2X3 with 2 fuel lines and 2 wires and maybe 1 or 2 vacuum lines. It is at the left front side of the engine looking at the engine from the front of the car.

Paul

Hey Paul, I've had the car a couple of years. I bought it locally from a guy here in town. Didn't pay much for the car. I was actually able to drive the car home...LOL...

The first issue was an erratic high idle condition. The car would start fine; however, as the car warmed up, the idle would increase dramatically. IIRC, somewhere around 1.8k to 2k. Found out that the plastic housing on the bottom of the air sensor plate was cracked. Replaced with new and that's when the running rich issue started.

The car has about 150K on the odometer; however, it runs really well with the exception of the rough idle at low rpms and the excessive carbon emissions...

Dizi cap, plugs (Removed W9DC and replaced with Super Plus 7905), and rotor are all Bosch. Haven't done the wires yet but that's next.

Current wires are Bosch;however, I've seen recommendations on Beru and a brand that begins with the letter K...I believe I saw them on the Bird...

My next step is recheck for vacuum leaks...and to see if either the cold start valve, fuel distributor or injectors are leaking...

I'm also looking into how to diagnose a faulty WUR....which you referred to as the control pressure regulator...

Thanks again Paul...

Best Regards,

Todd

Jitters · #8 03-09-2013, 01:41 PM

Quote:

Originally Posted by jimandsuzy

Is this a new symptom or is the car new to you? I bought a 500sec that had your symptom and just had to re-adjust the mixture to fix. No idea who did it or why it was out of adjustment but it's been fine now for about 3 years.

.

Hey Jim, as outlined in my previous post, the rich idle condition appeared once I changed the rubber air duct housing under the air sensor plate...and yes the car is new to me...didn't want to fool around with the A/F mixture without the proper guidance....

Best Regards,

Todd

pmckechnie · #9 03-09-2013, 05:14 PM

Todd, You do need to adjust the mixture if it was running reasonably well when it had the vacuum leak. That is un-metered air so someone probably adjusted the mixture to compensate for the extra air.

However you need to fix the cyl misfire first as that can upset everything else and you will have to go back and adjust the mixture again.

Adjusting mixture is a very easy thing to do after you have done it one time. I don't know for sure it you have a ECU or not and that will make a difference as how it is adjusted. I will try to explain how to adjust it if it doesn't have a ECU. All you need is a long 3mm allen wrench. Remove the air filter assembly. Just behind the air plate is a little 2 in high tower that is probably open on the top. With the engine running, put the allen wrench down in the tower. It should stop. When it stops, push it down carefully and turn the wrench back and forth until you feel it engage the adjustment screw. Turn the screw CCW just a little, maybe 1/8 turn or less. Remove the wrench and listen to the engine. If it is running better then try 1/8 turn again, removing the wrench each time. If it is getting slower or rougher try turning it CW 1/8 turn each time. 1/2 turn usually is too much in either direction. You have to just keep fine tuning until you get it sounding good.

When you get the feel of how to adjust the mixture, let me know and we will go into how I fine tune mine. It doesn't have a ECU because my engine is a EURO engine in a US car (long story). It never failed an emission test here in NC when they were doing them. Any car made before 1996 is exempt on the emissions now and gets a safety only inspection.

Paul

PS You may have to change the plugs. The ones you put in are resistor plugs. Some of these engines don't do well with resistor plugs. Mine doesn't like them. They cause a random misfire at idle when fully warmed up. I use NGK BP5ES.

Jitters · #10 03-09-2013, 09:27 PM

Hey Paul, thanks again for the information. I went out and bought myself a vacuum gauge to actually check vacuum. I still believe I've got more work in that area. Once I'm done there, then I will proceed to the next step.

I also sprayed a little carb cleaner on the two large vacuum tubes that are connected to the injectors and I noticed a change in the engine, so I believe I'm still sucking air into the system...there appears to be this beige sort of connector that connects the tubes to another large vacuum hose that goes under the Fuel Distributor. When I spray these connections, the engine bogs down.

As you mentioned, I still need to find out why number eight cylinder is not firing. Not sure if its the plug wire or not.

Will keep you posted...

Best Regards,

Todd