High Water Temperature
 

Since I have had this car the temperature has not gone over 85 degrees C. I have had no dash lights so today I removed the Instrument Panel and soldered the back of the dash light potentiometer. Presto I had dash lights.

After replacing the IP I started the car up and I didn't notice anything strange. The tack worked and I had oil pressure. I went in the house to let the car warm up (5 to 10 minutes) and I was going to drive the car for 20 miles to warm up the transmission so that I could make some adjustments on the transmission. Well when I went to get in the car the water temperature gauge was pegged. I checked the fluid level and it was where it should be. Since the only thing different was that I had taken the Instrument Panel out I decided to take it back out and recheck my installation. I could not find anything wrong, so I reinstalled it.

I restarted the car and it showed 89 degrees C. The needle quickly started going to 120C. I again shut off the car and checked the engine. The engine did not seem overheated. I had no problem removing the radiator cap from the fill tank. I could touch the valve cover and leave my hand on it.


Is there any possible connection between the Water Temperature gauge and the Light Potentiometer? Does the electric fan on the front of the engine come on when the engine over heats? It’s not coming on now.

Bill

Did you try the heat? Feel a rubber coolant line? If not, feel the rubber coolant line next time, is there hot coolant in the upper and lower lines? I'd guess either a contact in the back isn't being made as well as it should or your thermostat is stuck closed. Generally when the temperature sender quits it sends the opposite reading, to low. If the electric fan works it should kick in as a last resort cooling effort.

Micro,

I have almost always found that when something changes drastically, it was the last thing you did that caused the problem.

Since doing something to the instrunent panel shouldn't ever affect the running temperature of the engine, it is likely that you did something to change the temperture gage. Possibly an open ground circuit a or a stray voltage is getting to the gage. This is most likely the problem since the engine doesn't "feel" hot to you.

I'm assuming that you have an electrical temperature gauge since you didn't mention the model. Also, what is the time line between replacing the IP and soldering the light potentiometer?

P E H

It is a 83 300D (good idea to mention this or put it in your sig), he used a bad meaning for the IP there. It isn't the IP (injection pump) that we widely use here, he meant IP as in instrument panel. I'd pull the dash again and use some die-electric grease on the little pins to be sure it isn't a contact resistance problem.

Thanks for the suggestions.
 

I have bought but not yet replaced the thermostat (figured replacing it couldn't hurt). I also bought a light kit through **************.com. As my 1983 300D is not yet my driver car I can take my time fixing what's wrong and learning about the car.

Learning about the 300D is what I enjoy most about getting a fixer upper. My wife just likes saying we own a Mercedes.:D

MicroRacer,

First off, if this condition is new, then I agree with PEH that a new problem in an area where you were dinking around is most often the result of something you did, and not a new problem. When you did the repair to the instrument panel lighting dimmer, did you remove the dimmer from the rest of the instrument panel? If not, you may have damaged the circuit board with the soldering heat. If that is the case you may need a new board, or a new one from a recycling place anyway. There is also the chance that the signal wire insulation may be damaged and in its new position after being manipulated to get the gage cluster out, it is shorting to some structure in the dash.

I believe the way the temperature gage works, the hotter the engine temperature sensor gets the higher its resistance gets and the lower the voltage in the signal to the indicator in the instrument panel. This means with 12 Volts to the gage it will register no temperature and with a lower than 12 Volts signal in the sensor line it will register a temperature. The lower the signal the higher the temperature until the needle pegs. So, if your repair has damaged the signal connection for the gage you may have an inaccurate voltage signal.

When you start from cold iron what is the immediate gage reading? If it is not pegged or just off the peg at the bottom (low) that would be an indication you have, inadvertently, modified the signal from the sensor by adding a circuit element that was not there before you implemented the cluster lighting fix.

The most likely case is that you have introduced a place where the voltage signal is being consumed by a bad connection, or drained off either in the circuit board, the plug connector, or in the signal lead coming from the sensor. The circuit boards are old, and pretty sensitive to heat and handling. The plug connector may need to be cleaned or have the female/male elements tightened as they can become loose or pick up some dirt/corrosion products that can interfere with the low power signal. The signal lead can be damaged by pulling the cluster out and putting tension on the instrumentation wiring. This can cause the wires to be abraded against some of the dash support structure, possibly damaging the insulation, and develop a second path to an adjacent wire or some other place where it was not intended.

In any case it sounds like you are losing some of the voltage signal from the sensor, which the instrument sees as a lower voltage than it should and shows as a higher temperature than it should. The most likely place for the problem is where you were working last. Good luck, Jim