Operating temperatures
Steady state moderate load
Coolant/oil
194-195 F fluctuates, mostly 194 / 212 F exactly
In deg C 90 / 100
Tells me the coolant t-stat is 90 C and the oil is 100 C
2009 base car
Is this what others have observed?




Just ordered the 180deg thermostat from MHP - we'll see how that changes things, although there have been mixed results...




The 'ECU calibration' for the stock thermostat is bull****. (no offense intended)
There's no downside to reducing coolant temp in these cars, even if it's only a minor difference. As soon as I find a source for phenolic intake manifold spacers those will go on as well. Any little bit helps IMO.
If they wanted a 180 F stat they would have done so
Bringing on the fans sooner does nothing
The stat regulates temp and will actually open more to maintain 90C
So they act in opposition
The fan 'cools' and the stat 'heats' lol
I wonder what the actual rating of the lower setpoint stat is
80, 85 C ?
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Engineers actual size things based on a bunch of varables and conditions we aren't privy to
If I size a CB setting on a 10 MVA 4160 vac wye system it was done for a reason(s)
Raising it because bigger (or lower) is better does not apply
Some of those conditions, though, are longevity and fuel economy, which most people modding don't care about. So his snark is relevant.
Though, the 180 tstat is an often debated mod on every vehicle platform. Some people thinks it keeps the car from pulling timing, some people think it's snake oil.




It was not rhetorical - I was asking you. Why put an exhaust on. Why use better oil or other fluids. Why install/change anything that isn't available from the MB parts catalog if they did such a good job from the factory. Is that your stance on this? If so that's fine, but it's not what I believe.
Sensing and control/actuation is usually expandable wax or something
And the output is a valve
The wax is calibrated to put the valve in the middle of the valve throw/travel at setpoint
90 C oem...this way you have +/- 50% of the valve range to keep temp setpoint
An 80C will be calibrated to be in the middle also
But the engine makes the same heat
So to keep 80C the stat must open more
So with normal load the 80 may be at 75% instead of 50%
Now if load goes to 90C the valve may go to 100%
If load goes to 100C you may not have capacity to deal with it
With the 90C you have 50% headroom or capacity left
100C load may take it to 75% so you still have headroom
This is an example of why changing may not be prudent
In addition to the ecu calibration
Folks can do what they like but engineers usually have a reason
Though, the 180 tstat is an often debated mod on every vehicle platform. Some people thinks it keeps the car from pulling timing, some people think it's snake oil.
Lower would be better
But for emissions hotter is better, uses the fuel more efficiently and hence more power per unit of fuel
Niether will do much for charge temp
Without seeing AMG's docs, data and calcs it is hard to second guess their selection
It was not rhetorical - I was asking you. Why put an exhaust on. Why use better oil or other fluids. Why install/change anything that isn't available from the MB parts catalog if they did such a good job from the factory. Is that your stance on this? If so that's fine, but it's not what I believe.
You need to be sure your solution is better
imho that is hard to do without all the data




Let's say a 80C and 90C both open at 50% based on their respective temperatures, at that temperature. The thermostats are the same size, same flow, same everything except for the point at which they are open at 50%.
So they both have exactly the same overhead, except the 80C thermostat will be 100% open at say 100C versus the 90C being 100% open at 110C. Therefore they are both open 100% at 110C.
The reason for the 80C versus the 90C is that it is completely mechanical, and opens to that 50% 10C sooner. Thereby circulating coolant earlier, and overall stabilization of operating temp earlier. The ECU plays no part in this whatsoever, and does not need to be recalibrated in any way, with the exception of turning on the fans 10C earlier. In fact, you can turn on 'Desert Mode' in your car with the stock thermostat if you like, it will turn on the fans earlier to get more air forced through the radiator.
Sensing and control/actuation is usually expandable wax or something
And the output is a valve
The wax is calibrated to put the valve in the middle of the valve throw/travel at setpoint
90 C oem...this way you have +/- 50% of the valve range to keep temp setpoint
An 80C will be calibrated to be in the middle also
But the engine makes the same heat
So to keep 80C the stat must open more
So with normal load the 80 may be at 75% instead of 50%
Now if load goes to 90C the valve may go to 100%
If load goes to 100C you may not have capacity to deal with it
With the 90C you have 50% headroom or capacity left
100C load may take it to 75% so you still have headroom
This is an example of why changing may not be prudent
In addition to the ecu calibration
Folks can do what they like but engineers usually have a reason
Let's say a 80C and 90C both open at 50% based on their respective temperatures, at that temperature. The thermostats are the same size, same flow, same everything except for the point at which they are open at 50%.
So they both have exactly the same overhead, except the 80C thermostat will be 100% open at say 100C versus the 90C being 100% open at 110C. Therefore they are both open 100% at 110C.
The reason for the 80C versus the 90C is that it is completely mechanical, and opens to that 50% 10C sooner. Thereby circulating coolant earlier, and overall stabilization of operating temp earlier. The ECU plays no part in this whatsoever, and does not need to be recalibrated in any way, with the exception of turning on the fans 10C earlier. In fact, you can turn on 'Desert Mode' in your car with the stock thermostat if you like, it will turn on the fans earlier to get more air forced through the radiator.
Both 50% at their rating
Same flow too or close
But the engine is producing the same heat
So to reject more heat it needs more flow
Q = k x flow x delta temp
But if the engine is producing the same Q but must cool more, ie reject more heat, flow must increase since the drop across the radiator is the same for a given speed and oa temp
If the 80 is 100% at 100C
And the 90 is 100% at 110C
So the 90 is only 75% at 100C
So as load increases >100C the 80 will not be able to reject the heat and the system is out of control and can't keep up
The 90 can open more since it is only at 75% so it may keep up
For a given load the engine produces the same heat with either stat
To cool more (80 vs 90 or 10 deg) it must reject more
Since the radiator delta is constant more flow is required
The stat must open more




At 110C, the 80C is still open 100% while the 90C is now finally open 100%. Which one is flowing more at this moment? Both are the same.
The 80C thermostat starts stabilizing temperature earlier, because it is flowing more at that particular moment in time. Even at our max temp of 110C for this example, the 80C and 90C are flowing the same. There is a ceiling as far as how much either can open. The 80C thermostat will always outflow a 90C at ANY given temperature, because there is no situation where the 90C thermostat could possibly be open more.




So by the time the 80C thermostat maxes out opening at 100% at say 100C, that is the maximum possible cooling condition (flow). For either thermostat - they are both mechanically exactly the same, with the same opening and max flow rate, with only the spring changed. If the 90C thermostat is only 75% open at that 100C, then it is not in the maximum cooling (flow) state. At 110C, the 80C thermostat will have already been in maximum cooling state (flow) for the past 10deg, while the 90C is just getting there. The 80C will be slowing the rate of heat increase sooner than the 90C under every condition.
At 120C they are also both in maximum cooling state (flow), but since the 80C thermostat had already been in that state for a longer period of time, it is likely that the rate of heat increase has slowed much more than with the 90C thermostat.
The 90C thermostat in its maximum flow (cooling) state, is still only open as much as the 80C. It cannot open to flow more than the maximum for the 90C - it can't go to 110%, or increase the diameter of the inlet/outlet.
Last edited by BLKROKT; Aug 9, 2014 at 07:33 PM.




One is just controlling to a lower setpoint
The 80 is flowing more to the radiator as you said
The 90 is bypassing more
The 80 will reach its limit sooner saturating/overloading/overwhelming the system
At 110C, the 80C is still open 100% while the 90C is now finally open 100%. Which one is flowing more at this moment? Both are the same.
The 80C thermostat starts stabilizing temperature earlier, because it is flowing more at that particular moment in time. Even at our max temp of 110C for this example, the 80C and 90C are flowing the same. There is a ceiling as far as how much either can open. The 80C thermostat will always outflow a 90C at ANY given temperature, because there is no situation where the 90C thermostat could possibly be open more.
Last edited by Ingenieur; Aug 9, 2014 at 07:46 PM.
Now running without a stat allows the coolant to race around and through the rad uncontrolled except by engine revs, this car will over heat because the coolant flow is greater than the rad can dissipate heat.
A mod would be a larger capacity rad not reduced stat temp.
The opening for a 180 stat is no larger or smaller than a 190 so flow would be the same through both.




100C load, ie, a load that would stabilize at 100C with full flow to radiator
80 is 100%
90 is at 75%
If the load increases the 80 can't respond, the 90 can
Although flow may be ~ the same at 50% it changes with position
Due to seat are, oriface, whatever, the constant is Cv and varies with stroke
Flow = Cv x sqrt(press drop across valve)
We can debate this all day
I know how a thermostatically controlled valve works
They aren't only used in cars
There is a book by Fisher: Control Valve Handbook
Pretty much the reference standard
Not saying maximum cooling capacity changes ( although it may ) but that the throttling or range of control does
So by the time the 80C thermostat maxes out opening at 100% at say 100C, that is the maximum possible cooling condition (flow). For either thermostat - they are both mechanically exactly the same, with the same opening and max flow rate, with only the spring changed. If the 90C thermostat is only 75% open at that 100C, then it is not in the maximum cooling (flow) state. At 110C, the 80C thermostat will have already been in maximum cooling state (flow) for the past 10deg, while the 90C is just getting there. The 80C will be slowing the rate of heat increase sooner than the 90C under every condition.
At 120C they are also both in maximum cooling state (flow), but since the 80C thermostat had already been in that state for a longer period of time, it is likely that the rate of heat increase has slowed much more than with the 90C thermostat.
The 90C thermostat in its maximum flow (cooling) state, is still only open as much as the 80C. It cannot open to flow more than the maximum for the 90C - it can't go to 110%, or increase the diameter of the inlet/outlet.
As stated prev, the stat (190) is to provide fast warm up so the emission control systems can be brought on line. This is why a fault will occur if the ECU has seen a longer than normal time for warmup, usually seen when stat fails, open or extreme cold as we see here. Besides all benefit is lost with the 180 as the oil temp takes longer to reach operating temp and any benefit with the 180 is lost. Larger rad(thickness) will give you what you wish to achieve.


