fbgh2o

After my issues with the failed expansion tank cap today and testing the new expansion tank cap, I decided to monitor the temperature while driving around (using the climate control hack) and found them high.

I checked when I got home, idling in the garage, and discovered that the low speed fans do not switch on until the climate control hack show 103C and my Durametric shows 100.5C (it appears that the climate control is 2.5C to 3C high across the range).

This fan behavior seems a bit strange as they are supposed to come on at 96.75C for the low speed - I did not bother to wait for the high speed fans to come on fearing how hot it might get. I believe that this situation has always existed, even prior to the events today.

Interestingly the Durametric was also showing the following error codes

P0481 - Fan output stage 2 - open circuit
P1674 - Engine compartment purge fan,

both of which I attributed to the recent fan hack

Any ideas?

Many thanks

Pac996

P0481 - Fan output stage 2 - open circuit
P1674 - Engine compartment purge fan,

First one an open circuit could be a bad connection or broken wire.
Second fault refers to the fan on the rear spoiler lid.

Not sure of the way things are wired but if it's a series connection one fan having a bag connection would stop the other fan in series from working.

chsu74

My low speed fan also does not come on until 103C on the climate control hack. I never checked it before the fan hack but I thought it came like that. What temp is high speed supposed to be switched on?

fbgh2o

According to Loren on RennTech
Low Speed 96.75C
High Speed 102C

fbgh2o

However, they all work. I am pretty sure it's just the fan hacks which trigger the error code when you bypass the normal circuit with the manual toggle to turn on the fans

chsu74

Is this according to the climate control temp gauge or Durametric temp? I had my ECU flashed several years ago so I don't know if these settings were changed in the flash.

fbgh2o

Factory shop manual IIRC - therefore I would suspect DME. The climate control hack is not accurate and this has been stated by Loren and I can confirm that mine is about 2.5C to 3 C high at all times.

chsu74

I understand that climate control it is not the most accurate. However, if everyone goes by the climate control hack, it gives us a baseline to work with. Just like using a scale which needs calibrating, if everyone uses the same scale, we still can determine if there is a variance.

Ubermensch

I'm not usually one to doubt Loren, but I've been reading over this section of the manual recently for my own problems. As I recall Stage 1 comes on at 100C and Stage 2 comes on at 105C. There is also a dependance on some other factors (AC operation, outside temp), but those are the thresholds I recall. The 100C seems to correlate well with your Durametric reading.

fbgh2o

Can I ask the source? I would never doubt him either, but we have empirical evidence that supports your information and it would be very valuable to be able to reference the source.

Macster

The problem is various sources give different numbers. They differ, not by much, but they differ. Loren's numbers are as good as anyone's and probably better than most.

My source (Bentley manual for Boxsters) says the fans come on low speed at 100C (212F) and high speed at 216F (102C). (A high pressure in the A/C system I guess indicating extreme cooling is required which triggers the fans into high speed mode.)

I have confirmed the low and high speed temp trigger by monitoring the coolant temp using an OBDII code reader/data viewer.

However, the above is from a manual for the Boxster (up to year 2004 IIRC). It is not for any 996 model.

I can't find any info on when my Turbo's fans come on although I note they are listed at 3 stage fans, suggesting there are 3 speed ranges vs. 2 for my Boxster. I have never bothered to check when the fans come on in the Turbo.

From observing Obd data collected while driving I know the engine runs considerably cooler than the Boxster -- under the same driving/operating/ambient temperature conditions -- and I just don't worry about the Turbo and its coolant temperature as much. (Besides it has an oil pressure gage which I do pay attention to and even in 118F ambient temp has not given me any reason to worry.)

Now to be honest, I don't worry that much about the Boxster either cause while it appears to run hotter so far it has not seemed to be a problem.

Sincerely,

Macster.

Ubermensch

FSM for the 911. I'll dig up page numbers tonight if I remember.

S.

Ubermensch

Here you go: