I see quite a few posts about the W107 running "too hot". Often times, it seems the reports are of the engine running above 100C at times, etc, etc. Also, I often see the results best described as the "shot-gun approach" when it comes to diagnosis, ie replace this, replace that, etc.
First, let me suggest it be determined IF overheating is actually occurring at all. The W107, and many other MB engines are designed to run "hot" compared to what us USA folk are used to from Detroit/Japan. It is not uncommon for these engines to run close to the 100C mark, with occasional excursions above also common. Anecdotally, this seems "hot" when compared to the iron I'm used to, but it is normal and by design. If the excursions above 100 are frequent, and near/into the red, then you have cause for concern. While its true a 560Sl has an 80C thermostat, it is not fully open until 94C. Realizing this, its easy to see how the gauge in the dash could rise above 100 while the thermostat is reacting, assuming the two react equally for a given temperature, and hover near 100 during normal operation.
If an engine is overheating (really, to be accurate, we should say the coolant temperature is above design criteria), the obvious question is WHY? Really, there are only two reasons... Either the engine/tranny is generating too much heat for the cooling system, or the cooling system is not functioning adequately. Often, the assumption (and more often than not, correctly), is that the cooling system is "faulty"; however, this may not always be the case. One should consider the state of tune of the engine among the lists of items to check. An engine that is out of optimum tune, ie running very lean, or otherwise compromised will be guilty of generating more heat than the cooling system was originally designed to accomodate. The engine timing is also critically important to the state of tune, and the heat thereby generated. The tranny's health must also be brought into the fray as it can contribute directly and indirectly to cooling system inadequacies: directly by tranny fluid running above normal, transferring heat directly to the cooling fluid, and indirectly by inducing strain on the engine if not coupling/shifting correctly. Given that we are considering vehicles around 18-30 years of age, there may be more heat in the system than originally designed due to mechanical weakness in the drivetrain. Another list of things to consider can be called extraneous causes and can be related to dragging brakes, missing/mal-adjusted fan shrouds, tire aspect ratio and inflation, ratio of antifreeze/water, etc. Even the type and grade of oil can contribute to an engine producing higher levels of heat than originally designed.
If one accepts the above postulates, then it becomes incumbent upon the examiner to consider many factors aside from only the cooling system parts, ie clutch fan, thermostat, radiator, etc. In reality, for equipment of the age and mileage we are concerned with here, the cause will likely be a combination of these factors. The holistic approach must therefore be utilized in ascertaining a solution.
I suggest the following:
1. reSEARCH to determine what "normal" should be (expect a range).
2. Test to be certain overheating of the cooling fluid is actually happening. By test, I mean, utilize measurement devices beyond the gauge in the dash.
3. Check for extraneous causes. Focus on anything that has been changed recently, or serviced, etc.
4. Examine the systems, heat generating (engine/drivetrain) and heat exchanging (cooling system).
Somewhere within, the answer lies...
Author's note: The opinions expressed here are belonging to the author, and have been developed from years of mechanical experience with engines from motorcycles to freight locomotives and are by no means all inclusive or solely limited to the items mentioned.
First, let me suggest it be determined IF overheating is actually occurring at all. The W107, and many other MB engines are designed to run "hot" compared to what us USA folk are used to from Detroit/Japan. It is not uncommon for these engines to run close to the 100C mark, with occasional excursions above also common. Anecdotally, this seems "hot" when compared to the iron I'm used to, but it is normal and by design. If the excursions above 100 are frequent, and near/into the red, then you have cause for concern. While its true a 560Sl has an 80C thermostat, it is not fully open until 94C. Realizing this, its easy to see how the gauge in the dash could rise above 100 while the thermostat is reacting, assuming the two react equally for a given temperature, and hover near 100 during normal operation.
If an engine is overheating (really, to be accurate, we should say the coolant temperature is above design criteria), the obvious question is WHY? Really, there are only two reasons... Either the engine/tranny is generating too much heat for the cooling system, or the cooling system is not functioning adequately. Often, the assumption (and more often than not, correctly), is that the cooling system is "faulty"; however, this may not always be the case. One should consider the state of tune of the engine among the lists of items to check. An engine that is out of optimum tune, ie running very lean, or otherwise compromised will be guilty of generating more heat than the cooling system was originally designed to accomodate. The engine timing is also critically important to the state of tune, and the heat thereby generated. The tranny's health must also be brought into the fray as it can contribute directly and indirectly to cooling system inadequacies: directly by tranny fluid running above normal, transferring heat directly to the cooling fluid, and indirectly by inducing strain on the engine if not coupling/shifting correctly. Given that we are considering vehicles around 18-30 years of age, there may be more heat in the system than originally designed due to mechanical weakness in the drivetrain. Another list of things to consider can be called extraneous causes and can be related to dragging brakes, missing/mal-adjusted fan shrouds, tire aspect ratio and inflation, ratio of antifreeze/water, etc. Even the type and grade of oil can contribute to an engine producing higher levels of heat than originally designed.
If one accepts the above postulates, then it becomes incumbent upon the examiner to consider many factors aside from only the cooling system parts, ie clutch fan, thermostat, radiator, etc. In reality, for equipment of the age and mileage we are concerned with here, the cause will likely be a combination of these factors. The holistic approach must therefore be utilized in ascertaining a solution.
I suggest the following:
1. reSEARCH to determine what "normal" should be (expect a range).
2. Test to be certain overheating of the cooling fluid is actually happening. By test, I mean, utilize measurement devices beyond the gauge in the dash.
3. Check for extraneous causes. Focus on anything that has been changed recently, or serviced, etc.
4. Examine the systems, heat generating (engine/drivetrain) and heat exchanging (cooling system).
Somewhere within, the answer lies...
Author's note: The opinions expressed here are belonging to the author, and have been developed from years of mechanical experience with engines from motorcycles to freight locomotives and are by no means all inclusive or solely limited to the items mentioned.
