We have a 63 reg E class cabriolet with an overheating problem.
One year ago the car suddenly lost all power, temp gauge went to red and lots of engine noises.My wife was driving and obviously very worried especially about the loss of power. She left it for 5minutes the temp gauge returned to normal and when she got home I drove it and could not repeat the fault. Subsequently, having driven the car for a number of miles with no further issues, we had the coolant thermostat removed by MB and replaced at the not inconsiderable sum of £360.00.
We have had no further problems until Friday, when exactly the same problem arose and again leaving the car for 5 minutes reduced the temp and the problem has seemingly temporarily disappeared.We know that the fan belts pulleys can make a noise but the fan belts are in situ.
My wife has lost all confidence in her dream car and is worried this could happen on a busy road or motorway with disastrous personal effect.
Grateful for anybody else experiencing the same issue.
It is a 4 cylinder 2 litre petrol cabriolet with only 28,000 miles on the clock since new in 2013.

 

Intermittent issues are hard to diagnose and fix...

Was there anything in common between the two possible overheat events? Idling in traffic, hot outside, A/C on, stop and go traffic, coming off the highway/motorway, etc... How quickly did it go from normal 80-100* C to overheat? Any codes? Any coolant loss? How long between thermostat replacement and last overheat?

I said possible overheat, since the first case sure sounds like an overheat due to secondary indications of power loss and noise. My first thought, is it actually overheating? Not sure how I'd tackle this... easier things to check/do:

• Check radiator and condenser, behind bumper, for any obstructions (e.g. garage bag, leaves, etc..)
• Proper coolant level
• Insure no air pockets in system
  • Run engine with reservoir cap off, heat on full blast, till engine warms up, cap of reservoir, let it cool and top off coolant to proper level
  • Vacuum fill coolant system , likely don't have means
• Check cooling fan for proper operation
• Check thermostat
  • May not be possible with the new electronic ones, possibly live data via scanner would give some indications or codes
  • Older mechanical units could be dropped into boiling water to confirm they opened
  • Replacement is relatively inexpensive

From there, given the low mileage and intermittent behavior, less likely would be the water pump, radiator or blockage in system. All this is assuming the temp reading is correct and its actually overheating.

 

As this is my first post in this amazing and informative forum، I would like to thank everyone who contributed in sharing knowledge and helped others... I learned a lot from you guys and hopefully I will pay back some of what I get.


To the topic...
My case is similar to this one but I managed to link the ambient temperature with the condition of the fan.
Fan won't work properly if the outside temperature is less than 32° c!
However, it will lunch with A/C on but for some reason not working effectively as colant temperature get high.
If driving in relatively high-speed, colant temperature will be normal, though I don't know about the condition of the fan, but what I'm sure about is that colant temperature will hike up once I slow down or stop.

If ambient temperature is higher than 32° (in our region it reach +50° in summer ) the cooling system is working perfectly in keeping the colant at the normal range between 85 to 95 wich superb.
At winter, colant is always between 100 and 105!!

Any solution apart from changing the entire fan controller?
Can I install jumber wire between the different speeds relay, if any?


Regards,
Mukhtar

 

You have identified cooling issues related to fan speed controller. This is far more complicated that jumping relays.

The variable fan speed is directly controlled by the engine computer itself. You can check fault codes using an OBD scanner.

In addition the temp gauge displays a salted un-true number given by the ECU. This helps conceal temp jumps when the different components interact. The true sensor values can be retrieved via scanner.

In addition the coolant temp is regulated by the engine thermostat remotely controlled by.... the ECU! It opens only as much and when the ECU makes it when it wants to open it. There is a glorious map to control this efficiently.

In addition the coolant circuit is overwhelmed by the overheated dry pistons that transfer heat poorly into loose cylinder bores.

The results are that engine cooling is often ineffective. Engine pistons store heat that vaporize oil onto dirty GDI valves and cause "extreme heatsoaks" that lead plastic sensors to send oil into... exhaust Lambda. Then you get a misfires with $10k harness repair.

Because engine lubrication requires additional energy, a "gas saving" oil is used at reduced pressure to guarantee excellent savings.

Standard issues related to the above systems develop under normal driving conditions when engine is kept below 2000.Rpm. Very low cooling is achieved for maximum "gas savings".

Under these standard conditions the fan often runs high while the temp display remains perfectly normal.

Keep an eye on both coolant and oil level. Watch for leaks developing as the normal result of extreme stock conditions. The engine fan is a fairly robust unit.


++++ Experimental upgrades...
Sometimes normal standards are not practical!
In 50°C summer saving gas can be less a priority than preserving cooling system integrity.

It was discovered that experimental oiling improvements may help restore effective cooling your engine needs.

 

Thank you for your prompt response...
Just to clarify that I'm referring to M276.958 na at SLK350 2013,
Neither thermostat nor the pump are electronically controlled.
I'm monitoring my colant temperature through an OBD adapter using Dash Command app. So the temperature I'm reading is slightly more accurate comparing to the lying gage.

I did small trick to misslead the ampiant temperature sensor to read higher temp and I noticed the impact on the fan speed immediately.


Any low-budget solution?

Regards
Mukhtar

 

You know your.... SLK350 '13 M276 has no electronically controlled thermostat or pump...

This being the W212 forum, our M276 engine Tstat is remotely controlled by ECU as mentioned earlier.
The coolant pump is belt driven.
Aux electrical pump hardly involved with bulk cooling.

The ambient bumper sensor is only taken in considerations under specific conditions when the vehicle is moving.

The main issue of coolant temperature is related to the engine core. Once the core heat is circulated out by better oiling, the stock coolant system is no longer troublesome.

So that's why I pointed you towards experimenting better oiling else stock is the perfectly normal fare as Mercedes designed it.

Perhaps your Mercedes uses different local engine options than California does... entirely possible.