[Blue-S]

I had some time this evening to drive a bit and collect some data from the HVAC control panel's diagnostic mode as explained above. The car was a 2000 Boxster S 6-speed, with a new Porsche water pump and a 1-year-old standard replacement thermostat (presumed to be 80 deg C). The A/C compressor was off throughout the testing.

* During warmup, with the temp gauge needle exactly on the "tic" mark above the "8" in the "180" label, the HVAC panel (in 6c display) read 79 degrees C coolant temp. That converts to 174 degrees F.

* After allowing coolant temp to stabilize by driving approximately 10 miles with cruise set at 71 mph indicated in the digital speedometer display, I saw the following in the HVAC panel diagnostic mode:

Outside Temp Average (5c display) = 30 deg C (converts to 86 deg F)

Coolant Temp (6c display) = 91 deg C (converts to 196 deg F)

Vehicle Speed (20c display) = 111 km/h (converts to 69 mph)

RPM (21c display) = 2700

The coolant temp gauge needle in the instrument cluster was pointing straight up between the "8" and the "0" of the "180" label.

Oil temp was unavailable in the HVAC control panel diagnostic mode, because (I think) the 986 Boxster does not have an oil temp sensor in stock form.

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When I returned home, I idled the engine for a while and gathered some more data:

* at 100 deg C (6c display on the HVAC) the gauge needle was approximately in the middle of the "0" in the "180" label.

* at 102 deg C (6c display on the HVAC) the right side radiator fan came on. This correlates with the specification in the Bentley manual for HIGH speed (stage 2) fan. The coolant temp crept up to 104 deg C (219 deg F) and stayed there for at least 5 more minutes with the right side radiator fan running. The gauge needle was at the right edge of the "0" of the "180" label when the HVAC was displaying 104 deg C coolant temp.

It is apparent that I have a radiator fan problem on my car. According to the wiring diagrams, both left and right side fans should be controlled at the same speed (stage 1 or stage 2) at the same time. It should be pretty simple to begin testing at the relay locations under the dash, since the relays seem to follow the standard ISO terminal definitions. I'll start with my Fluke 88 meter and a fused jumper wire...

So, what's going on here? These coolant temperatures do not match what JFP in PA, cnavarro and Jake Raby have posted on multiple occasions. Is the DME lying to the cluster and/or the HVAC control panel? Is the cluster lying to the HVAC control panel? Is the HVAC control panel lying to me? Or is the HVAC panel diagnostic mode accurately reporting the coolant temp as the DME reads it from the ECT sensor? None of the scan tools I have access to will read DME data, so this might be the push I need to buy the Durametric package...