Originally posted by Anri
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Hi Anri I have to dig in to this, for sure the ECU checks if the normal operating temperature is reached in xx time. I would expect that parameter to be adjustable to prevent the error code from triggering or just disable it.
I suspect that lambda regulation kicks in after xx seconds of operation or once the front lambda probes exceed a certain voltage threshold. If started in -40°C environment it doesn’t take up to 70-80°C Coolant to enable lambda control. Enrichment tables are meant to add fuel during cold coolant temperatures to still target lambda 1. Currently only for short periods or really low temperatures a richer mixture is allowed. For an equal operating condition more fuel has to be injected on a cold engine as on a hot engine and the lambda value would still be equal once measured in the exhaust. From an OEM perspective you don’t want the lambda controller to adjust this, it has to be on target from the base.
In some engines the engine block and cylinderhead runs different temperatures by using double thermostats. On (current) BMW engines the (electric thermostat) temperature is controlled by load conditions (85 – 113°C). Full load will trigger to lowest to get maximum power from the engine. The highest are used in part load, ditching more heat will have less efficiency, the higher the better in terms of efficiency. New (BMW) engines have ditched the electric water pump and brought back the mechanical driven pump back. Engine developers used the mechanical driven pump for a reason, when increasing engine speed more horsepower is created (or better kiloWatts) and more heat loss. Once the pump rotates higher the massflow of medium is also higher (Q = massflow (m) * constant (Cp) * delta T(dt) ). Perfect as it is equal to power (Power = Torque * 2*Pi* engine speed in Hz).
On the test engines I have from OEM the coolant outlet temperature from the engine is controlled by the ECU. The coolant inlet temperature towards the engine needs to be controlled to ~70°C all time. I personally think that here the debate starts on the thermostats. If for some reason the radiator outlet / motor inlet temperature becomes too high the results is higher coolant temperatures than the thermostat is specified. From the M52 engine or maybe earlier BMW engines had a radiator outlet/motor inlet temperature sensor to control the auxiliary fan. Might not be present on S54 (I am not sure). It would be helpful to monitor this temperature in case the engine performs on higher temperatures than specified.
When fitting a lower opening thermostat I would suggest the complete delta of temperature is dropped and as a results prevents it from running on high temperatures. I would personally look for a root cause as I would suggest the radiator heat exchange might dropped by contamination (or blocked condenser) and or the water pump lost efficiency. There are probably more parameters to take care off.
I don’t know for people that currently experience issues if the environmental temperature has increased over time? As it is +25 years back the S54 was developed it might cause issues. Once no other options are possible to drop temperatures (increased waterpump flow, increased heat exchange from radiator, fans, etc) I would expect Anri’s thermostat to work as a (low cost) solution.
I believe on the S38 /E34 M5, different waterpump pulleys (smaller diameter to get more flow) were used in hot climate version. Also 1st and 2nd stage aux fan thermoswitch sensors were used to cool the engine better ways. I never seen thermostat difference.
I usually come by to a customer who is racing with a lot of S54 engines powered cars, currently even has the newest GT3/4 models as well. On none of these the thermostat opening temperature is changed, and no issues there. But our European temperatures might be relevant.
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