Retrofitting a third radiator (center) to the 3.4?

  • I also have the 3.4 L 996 and have had the earlier opening thermostat and new water pump in it since the end of 2019. My temperature is actually always around 82 degrees according to the display (when it's warm) When it's really hot, the temperature can go up to 90 - 95 degrees for a short time

    I think this is normal and safe. As I'm not planning to use the convertible on the track, I'm not going to fit a 3rd radiator. What would be the point.

    Do you have a link to the thermostat?


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  • I ordered mine from But the one from cpt.miller is actually the same.

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    :hilferuf: ich fahre auch Porsche... :thumbsup:

    Selbstschrauber GEN On Board :headbange

  • The water temperature that is displayed corresponds approximately to the temperature at which the cooling water leaves the radiator. This temperature is well below the temperature of the coolant in the immediate vicinity of the cylinder head or, even better, in the vicinity of the cylinders themselves.

    At least according to Cartronic-Motors Time Over (p. 49).

    Greetings Peter

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  • The price from CDP is really cheeky. The part is available as an accessory for 30-40 euros.

    The original equipment manufacturer is Metzger, and the Porsche part number and trademark can be found on the part. I have installed it and it works great.

    If you need it, here is the data:

    Part number:

    METZGER 4006157

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  • For me it was incl. :D

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  • Thanks, just ordered.

    Do you also happen to have the part no. of the oil pressure thermostat to hand...:-))

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  • Munichdriver - have you ever spoken to Paintmayer, I believe they already install the earlier opening thermostat during a revision.

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    Porsche 996 4S - Spaßauto - seit 05/2016

    BMW 118i Cabrio - Stadtauto - seit 03/2016

    Mercedes E350 CDI 4-Matic - Langstrecke - seit 02/2019

    Historie: Passat Variant 35i, Honda Civic (4. & 5. Generation), Polo 6n, Passat Variant 3B, Golf 4, Passat Variant 3C, Mercedes Viano 2,2, Mercedes Viano 3,0

  • However, I believe that the original cooling system is inadequate.

    Unfortunately, the 996 has no oil temperature display. Nevertheless, I am sure that the oil was often too warm in my car.

    Once the coolant temperature was over 100 degrees, the oil was no longer cooled properly.

    Even with 5w50, I only had just under one bar of oil pressure in this state.

    Or am I making a mistake? The lower the coolant temperature, the better the oil is cooled, right?

    First of all: Oil pressure of 1 bar warm at idle is no reason for concern, and 5W-50 oil gets a few degrees warmer than 0W-40, for example, anyway; this is the result of internal friction ("viscosity").

    If you are worried about whether the oil is too hot or how hot it should be, you can take a mental cue from the air-cooled engines, which are considered indestructible and were also cooled to a large extent by the oil.

    In the 993, the first stage of the front blower only started at an oil temperature of 110°, measured at the feed point in the pressurized oil circuit, i.e. the coolest point.

    The oil temperature is also measured on the 996, but in the sump, where it is normally even warmer. As the oil flows through the water-oil heat exchanger before being fed into the system, it is slightly warmer at operating temperature than the water coming from the thermostat. In normal operation, this is between 85°C and around 100°C, above which the thermostat has regulated out. The engine temperature, which is displayed via OBD or the "climate hack", is measured at the outlet of the water at the engine and is therefore the same or higher than regulated by the thermostat. Porsche considers 90°C (+/-5°C) to be the usual "operating temperature" (for diagnostics / old manual).

    I see no basis for concern about the oil temperature.

    But what about the water, especially the temperature of the LokaSil cylinder walls, which are said to have a tendency to ovalize the bore?

    The criticism mentioned above, which Cartech copied from Hartech, refers to the position of the thermostat at the water inlet to the engine instead of at the outlet and is, in my opinion, based on a technical misunderstanding on the part of B. Hart (Hartech).

    If the cooling surface is not sufficient to keep the water temperature in the desired range at high load/outside temperature and low speed (or the air conditioning system requires this), the radiator fans start up in several stages. This should happen from about 105° C water temperature.

    Additional cooling would only be required if this were not enough, in which case an additional center radiator could help.

    Incidentally, the water in the 991 constantly reaches 105° C in "normal operation", even under low load, as does the oil.

    It has already been written many times, but I will write it again: a thermostat with a lower opening temperature lowers the engine temperature mainly when it is not needed or even harmful (condensation, oil dilution, etc.).

    Critical in terms of cooling performance is not high speed (cpt. Miller: "When I'm speeding along the highway at speeds above 250 km/h, I'm sometimes afraid that the engine will cool down too much..."), but slow driving at high outside temperatures and loads. If the cooling water temperature in the control range of the thermostat and thus the difference to the outside temperature is around 10°C lower, the cooling system only has around 83% of its capacity compared to the factory design at an outside temperature of 30°C, for example. If the situation becomes critical, the thermostat will still have regulated out 10° earlier than the "normal" thermostat, so it will no longer help. However, the fans only start up at the temperature programmed in the engine control unit at the factory.

    If you believe in the "colder" thermostat as life insurance for the engine and want to do it right, you would also have to a) increase the cooling surface (e.g. center radiator) b) switch on the fans earlier (reprogram the engine control unit), even better c) use a map thermostat whose control temperature is adjustable, such as in the 991 (which is also installed there for other reasons).

    The lower temperature could be of some use if a high load, which hypothetically overloads the engine or cooling system, only occurs for a very short time, so that the heat capacity of the engine and cooling system, which is at approx. 10° lower output temperature due to the "colder" thermostat, is utilized. 325 hp rated power / approx. 240 kW generate approx. 80 kW heat output, which goes into 23 liters of cooling water (and 10 liters of oil and approx. 100 kg of metal). The heat capacity would be approx. 250 kWs/°C. In other words: maximum output with a regulated thermostat brings the temperature to where it would be with a "normal" thermostat after around 30 seconds.

    What I would do if I owned a 996 (also applies to all successors): clean the radiator inlets more often, especially in the fall, remove the front panel from time to time; make sure that the water pump is intact or not too old.

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