Mike J

Check out:

https://rennlist.com/forums/993-forum/401383-964-993-control-arm-bushings.html

Cheers,

Mike

North Coast Cab

Yeah, very nice, but what does that have to do with the oil temp sender?

Mike J

Nothing! I posted the wrong link....now if I can only find the one that I meant to post...sorry!

ppressle

I like the idea of adding resistance to lower the temp the fans come on. But, do we really know that this does not also affect other areas like the ignition advance curve? Is it really as simple as just controlling the fan?

I was not sure about that, so I modified the fan relay to turn the fan on high when the low speed fan was requested.

Pete

Leander

This all seems to imply that the Porsche engineers didn't know what they were doing in the first place. I find that hard to believe.

North Coast Cab

I beleive the design was for a street environment. When the oil temp reached the sender level it would switch the fan on and eliminate further heating. Seemed to work ok locally and on the highway.
For a track application it would be beneficial to have the fan on sooner and thus slow the rising temperatures. Plus, when you cooldown or slow the high speed fan can reduce the oil temps fairly quickly.
I am installing the switch, but it would be nice to have it automatically fire the fan.

helmet155

Is there any new news on this?

Both options seem like a better 'automatic' solution rather than the bypass switch, I personally dislike hacking up a harness.

The BMW type of oil temperature switch would be a preferable solution, fan on at 91 or 99C..parts can be found at Pelican HERE

Otherwise I may wire in an override switch on the ballast side of the connector, with switch and relay, therefore no modifications done to an expensive under dash harness and the only mod will be done to the ballast resistor harness (cheap replacement).

chaoscreature

If you google temperature switches there are a ton of them out there in just about every temperature range you could ask for. I would assume that the engineers at Porsche had a pretty good idea of what the proper operating temperature range is for these engines. Making the fan turn on earlier will not help prevent overheating, just postpone it. I would be looking at adding more cooling power and maintaing the factory temp's.
Remember that a lot of the automotive temperature switches are designed to be used in water jackets which are typically 20deg+ cooler than the oil temperatures.

helmet155

As an automotive engineer, I appreciate your comments regarding our skillset and knowledge. I must add, our design intent is often thwarted by those pesky people in management, purchasing and even worse: the general assembly location.

Elephant Racing has a great graph relating engine temperature to longevity that I like to reference and in this case, the 993 engine tends to get a tad hot. I'm not an original owner, nor is my 993 within the warranty period so I am not going to return to the dealer to complain about the loud fans or the headlights dimming when said loud fan switches on only to be told it's normal and mark Porsche quality and dealer service poorly on the survey I would have been sent by JD Power.

Regardless, heat is the enemy and I want to keep the needle around 8:30.

Mike J

Cool graph, but what research is behind it to get those numbers that determines that curve?

I do totally agree though on the idea, and use my manual bypass all the time to keep the needle never beyond 9:00, usually below all the time. A lower turnout temp switch would make sense to me, but I am too lazy to try time, so I just use the manual switch. Feels like the good old days when you have to pull the choke, having a manual operation depending on the situation... :-)

helmet155

Mike the graph was referenced by Steve Weiner in an old post I read and I bookmarked it. If Steve mentioned it I figured it had some validity.

The BMW switch would be a good way to have automatic operation come on lower, you can go with 91C or 99C...I'd prefer 95C.

I will see if I can get one at the local BMW dealer and run some DVOM tests on it...

chaoscreature

Industrial automation companies like Omega and others sell both custom preset and adjustable temperature sensors in a variety of fitting configurations.
Manual switches are fun until you forget to switch them on one day (speaking from experience).

Archilla

This months Grassroots Motorsports has a good article on choosing oil viscosity based on a target operating temp. Short version, operating oil temps which are too low are also not a good idea. Lower is not universally better (beyond a certain point).

helmet155

OK, after much fun on my last day off of my 3 day vacation I pulled the temperature sender and measured the resistance at 230F, came up with 690 ohms. 212F was 900 ohms. I'm shooting for the fan on at 195F so I am going to add a 2500 ohm resistor in parallel to the sensor to trick the CCU into turning the fan on at 195F.

Quite possibly I will end up adding a rheostat in parallel to the sensor for a quick trim of the on point.

On to finding the proper resistor now.