Join Date: Jun 2013
Location: Madison Wisconsin
Vehicle: 2000 230 SLK Linaritblau...65,500 mi; 18" Speedline Corse, Yokohama ES 100, 245/45 x 255/35
Other Toys: 88 XJ 140; 58 Cadillac Eldorado Brougham; 88 Alfa Milano
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With regard to cooling systems and temperatures, I have gotten very hands on with the cooling system of this car. Having experienced similar issues with various aluminum and alloy based engines of all types, I decided to take the obvious route and address the cooling system rather than sensors, etc.
Number one...I flushed the system, draining the radiator, expansion tank and block. Over the years, my car had evidently "accumulated" various types of coolant. I purchased the appropriate MB coolant, and yes it was 3 times more expensive than the most expensive "off the shelf" brand. However, I have learned through their oil filters alone...they produce a superior product.
I have always run aluminum based or alloyed engines with a good coolant (previously Advance, due to low levels of silicone*), and distilled water w/o sodium. No need to explain.
Furthermore, the percentage of coolant to water mixture, will additionally have an effect upon your operating temperature. If your mixture is more than 50% coolant, you can count on a higher operating temperature. Any coolant will disperse heat slower than a more purified form of water. A mixture of 40% coolant to 60% distilled water works best for my vehicle. The gallon of MB lifetime coolant I purchased (as well as my operator's manual), recommends no more than a 45% coolant to 55% water mixture.
In addition to these other factors, my expansion tank float had become defective, due to the rubber seal at the top of the "float/pellet" becoming dislodged. This made "sealing" the tank (radiator), cap when the coolant level was filled...impossible. New tank with float...53 bucks, eyes closed replacement.
Silicone Dropout. A local "radiator" guy wrote an article for Car & Driver years ago about the high levels of silicone in "aftermarket" coolants. Even the cleanest radiator core, with perfectly clean tubes can have silicone dropout. I have experienced this with a 2600 Alfa Romeo. After cleaning, flushing, sonic cleaning...the only answer was silicone dropout, and a new core. In this case, with the same mixture of distilled water, and Advance coolant, the engine ran at it's "normal" operating temperature.
With this in mind, the suggestion of a re-core would not be unreasonable. However, the lowering of operating temperature from engaging the heater is not in and of itself an indication of a faulty cooling system. Any engine with a properly operating system will do the same. In most cases you are simply increasing the number of radiator cooling fins by 1/4. It is partly why there are single; double; and multiple "rows' of cooling fins within various radiators.
With regard to my SLK 230...after these "corrections" and learning the thermostat temperature for this "model" is 87C, my car runs at 82C on the open road...and 90C - 95C in stop and go traffic. As it should. The local dealer confirmed this. The cooling fan comes on at various "percentages" depending upon what the engine is "calling" for.
I found all of my sensors including the temperature gauge (which was checked with an internal thermometer), to be absolutely correct. This also included the coolant level sensor.
Last edited by kentsteine; 07-14-2014 at 02:35 PM.