My car, with new Radiator and proper fluid and new temperature sender will commonly show over 100 C (maybe that 105 shown up there in that picture) but a quick check with a Infrared thermometer never shows more than 91 C. My problem appears to be with the gauge itself. It will jerk up there and then jerk down fairly quickly and sometime read normally for a while. It is inconsistent. Could be grounding or could be a voltage issue to the gauge. Don't know, but I can live with it as long as I know the real temps. One of these days I will mess with it and fix it.

Check it with an infrared Thermometer and confirm its really correct before you do anything else.

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1983 300D-Turbo - Deep Blue w Palomino MB Tex (total loss in fire 1/5/09 RIP)
1995 E320 W124 Polar White/Grey Mushroom MB Tex
2005 F150 Supercrew - Arizona Beige - Lear topper
1985 Piaggio Vespa T5 - Black and Chrome

www.cphilip.com

Gauge/sender check is to put a 38 ohm resistor in place of the single wire.sender...that equates to 100C on gauge.
Radio Shack....99 cents . Use a close tol. one.
I have one made up in the tool box for instant gauge testing............

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A Dalton

Guys, I stand corrected; looking at Johnathan's photo, it appears that's about the temp that my high fan turns on (105, not 115).
In my '86 manual, it lists a thermal fan switch 105-115, so I assumed it turned on at 115 and off at 105. Maybe at 115 it goes into hyperspeed - ha.

Arthur is right on about the junk that can collect between the condensor and radiator.

I had the infamous low-speed resistor burn out. I thought it was the pressure switch, as stated above, but when I dug down and looked at the resistor, it was pretty obvious (wire fried). I ran a secondary wire from the low-speed relay to the resistor to permanently solve that problem.

DG

S class



That is where you went off track.
The 86 schematic can not be used b/c they used a 105/115 temp sw.

The '88 and up do not use the 105/115 sw...they use a two wireThermistor sensor that triggers the ACC Panel at 105 cut-in, and that triggers high fan. The R factor decreases as the temp increases .. [ neg./ coef. thermistor] ..that is what allows one to change the cut-in of high fan by bridging that sensor...the R in parallel drops the Total R of the sensor, so you get a lower cut-in.
But you were absolutely correct on all other aspects and I comend you.........................Archieves

>


Actually, The 115 is a/c compressor cut-out if temp gets to 115.
The fan is the 105 section of that sensor.

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A Dalton

I used to own a radiator shop. A couple of points that I'd like to toss out..... Between my partner and I we have many years working on vehicles. I have only seen one water pump that caused overheating. The fins on the impeller had corroded away. My partner had only seen one other..... the impeller had gotten loose on the shaft and wasn't turning at shaft speed. Yes, a water pump can cause overheating but it is very rare.

Another is how a cap affects the cooling systems performance. The basic purpose of the cap is to pressurize the system. Each pound of pressure raises the boiling point approx 2° (F). Higher pressure does not increase the efficiency of the system. It merely keeps the coolant from becoming steam. I ran my 450SEL up hwy 15 through Cajon Pass to Barstow, CA at over 70 MPH with the a/c on without the cap even on. This was on a warm day. Only found that the cap was off when I stopped to get gas and it spit some coolant out due to heat soak heating the coolant to the boiling point. No change of operating temp.

A radiator can appear to be good but may have reduced efficiency. Scale can form on the inside of the tubes and reduce the heat transfer from the water to the tubes. Often this can't be seen and the radiator may flow quite well. If the radiator is like the ones in my 500SEL and my junk 420SEL it's an aluminum core with plastic tanks and one row of giant tubes. And these radiators don't have a cap on the top where you can see down into several of the tubes. The tubes can get scale built up on the tube walls without really affecting flow. Unlike typical radiators used in the 60s, 70s and 80s with multiple rows of smaller tubes that are much more prone to flow restriction due to scale accumulation and will show reduced flow quicker with scale accumulation. The second thing that happens is loss of tube to fin contact. In a copper/brass core radiator where the fins are soldered to the tubes the tubes try to become round as pressure in the system builds and eventually this breaks the solder bonds. I don't know how they bond the fins to the tubes in the aluminum radiators. I'm assuming a thermally transmissive adhesive. But reduced radiator performance may not be readily obvious and may only show up in marginal situations (such as a hot day). In it's beginning stages it's pretty hard to isolate a radiator with reduced efficiency without a known reference.

Karl M.

I forgot to mention about my experience with ignition timing. As some of the other posters mentioned something about timing and mixture. Retarded timing can cause all sorts of problems including: poor performance, poor gas mileage and the engine may run hotter than normal. Maybe quite a bit hotter than normal. And a continuing buildup of heat even at idle. (DAMHIK) Doesn't hurt to check your timing.

As one of the other posters remarked, running lean can cause an increase in operation temperature. If it's this lean you will probably also notice knocking from detonation. PROBABLY but maybe not.

Karl M.

if your aux fans are coming on when you temp climbs to 110c but your temp is not coming down you might need to flush your system and add a fifty fifty mix of mb coolent along with an addative called water weter this helps in heat transfer in cooling system do to bubbles forming in water. Water wetter helps prevent this an aids in heat transfer for better cooling.. a lot of guys who have these. cars in hot climates use this product to help cooling of the engine..
Bob

I think that the suggestions that point to verifying that you are even overheating at all are on point.


I like the idea of using a 38 ohm resistor to verify that your gauge reads 100c. That's a good check. Follow up by measuring the resistance of the temp sensor (The single pole one that goes to the gauge) at ambient and comparing it to the chart to make sure it's accurate.

I recently replaced temp sensor, it was 20 degrees off. It was reading just over 60 when the temp was really just over 80. That's typical of negative temperature coefficient sensors, they tend to drift higher in resistance, registering a colder than actual temperature. It is possible for them to drift the other way, but it isn't as common in my experience. It is also possible for the gauge circuit to be off, so that's why I really like the 38 ohm resistor test.

If you've verified that your gauge is accurate, and you're still experiencing heat rise, check the thermostat. We'll assume the radiator is good since it was replaced recently.

Using an IR thermometer (or a $1.99 digital meat thermometer taped to the hose), measure the temperature of the top hose coming out of the water pump after the thermostat. Start the car from cold and let it run. What you want to watch for is when the thermostat opens, the temperature should rise quickly on the thermometer. Now, the water coming out of there should be no hotter than the temperature rating of the thermostat when the car is first warming up. Under load is another story, but what you want to verify is that the thermostat is opening up at the right temperature from a dead cold engine. Also, note the dash gauge temp reading at the moment that the thermostat first opens. Compare that to the rating of the thermostat. You'll know quickly if something doesn't jibe.

If the water coming out of there measures much hotter than the thermostat rating, then replace it. You can also squeeze the hose to "feel" the flow, and assess if it is restricted or trickling. It should start out slow and begin to flow fully as the motor heats up. Watch out for belts and fans. Also, a lot of folks are missing part of their fan shroud and aren't even aware that there is a second ring shaped piece that snaps into the main shroud. That could lose you a lot of efficiency, but that shouldn't be an issue at cruising speed. That will get you hot at a stop light.

Yes, a blown head gasket is possible, but would probably manifest other symptoms as well. I'm betting something simple if you're not having other serious issues or noticing oil in your coolant.


-tp

If you convert 110 celsius to fahrenheit you get 230 degrees. I don't know for sure about Merc's being aluminum and all but, 230 is not that unusual on modern engines. Most people don't understand that the pressure cap is there to raise the boiling point of the coolant so that it can run there without boiling off the coolant. Tom