gobs

Went to the lower temp thermostat, third radiator and replaced the water pump, no problem with high temps. The last couple of days it has been 90 plus extreme humidity no issues. Worth the money.

RngTrtl

Pretty much this. it is normal for the true temp to wonder from say 190-220.

911Syncro

Very interesting thread, but I have a quick question. I'm still newer to the car, perhaps I haven't researched enough, but how I can tell if the radiator fans are coming on while driving? It seems on other cars I can hear them, but have never heard the fans on the 996 (Mk.2). Thanks.

Jeff95M030

My 1999 club racing 996.1 (SP996) overheated last year at NJMP (ambient temp 95 F). Cleaned the crap from the front of the radiators, fixed a bad L temp sensor, then installed a third radiator, new water pump and low temp thermostat. Using distilled water and water wetter. Also added the GT3 bumper with factory ducting to each radiator and put in a simple switch to manually activate both front fans. At full race speeds last weekend (WGI) the car ran a steady 190-195 degrees, though ambient temperatures were pretty cool - maybe 75 F. I run the fans manually when under yellow, staging or in the pits and it stays around 180 F. Next winter I hope to fabricate some baffles to improve flow through the side radiators. Here's the manual radiator fan control hack:

https://rennlist.com/forums/996-foru...tment-fan.html

Mike Murphy

True

time4a911

Thank you for the input.
1) I have flushed the system twice, once because I a leaky hose and second when the t-stat was installed.
2) Radiators have been brushed cleaned and blown with compressed air.
3) I assume my indy-shop checked for pockets.
4) Car is all factory, no after market bumpers
5) I really don't want to ghetto rig the car with the "fan mod" and a switch.



Question:
Will the fans engage with the A/C on, even with bad resistors?


Other solution:
https://www.vividracing.com/catalog/...150757633.html

ohlins8990

For what its worth, my 99 will have the needle go from between the 8 and 0 of "180" (194 on my obd reader, 92c on the dash display) and go to where the needle is between the 0 and unmarked line (seems to be 220F according to my obd reader, 112c on the dash display). In low to mid 90's I have not been able to get the temp above the unmarked line. It is a bit disconcerting how much the 996 seems to rely on its fans to maintain its cool. I proactively replaced the fan relays and have cleaned the rads, replaced WP, and OEM thermostat, and updated the cap to the 04 rev. Running the Porsche coolant at 50/50.

Mike Murphy

For this reason, the folks that are still running these higher temps, even after putting in all these tweaks, flushes, and mods, the simple fact is, many of these 996s still run hotter than we'd like.

112C (233F) is pretty warm for Coolant if you ask me. Mine has only gotten to 107C. Not sure what cooling system pressure is needed to keep water from boiling at these temps.

5CHN3LL

The previous owner had the center radiator installed along with all of the aero/aero II parts. I de-gunked the radiators prior to this trip, but no other cooling system maintenance other than verifying coolant levels haven't changed and no visible fluid hanky-panky (oil in the coolant/coolant out the tailpipe kind of hanky-panky).

I did not datalog this trip, but I have a decent idea of how my gauge tracks acutalish data. The temp was nominal, right in the sweet spot of warmed up but not hot (again, by my decidedly imprecise calibration), even when we were driving at low speeds (35MPH) in 90-100 degree F ambient temps with the AC on after some higher-speed pulls. I was pleasantly surprised that NOBODY puked up any coolant, but most of the cars present live in the desert full-time and were probably better prepared than my decidedly half-a$$ed efforts.

But at least I put the spare in the frunk, right? *sigh*

time4a911

I did all this with the exception of a new water-pump and a 160 thermostat.

On the highway, with a 169 t-stat the temperature stays at the 180 line regardless of how hard I drive it. In city traffic, I can baby it and watch the temperature climb rapidly.

Again, I am pointing fingers at the fans and thier engagement point.

Has anyone tried CSF aluminum radiators? At roughly $1,000 I am ify about it.

Thank you all for taking the time to post real life experiences with the heat issues.

Mike Murphy

Certainly a factor. The cooling fans in my car don't even come on until the temp goes to 97C. That's the low-speed fans. The high speed fans come on at 102C (215.6F), while the thermostat is fully open at 210F. So if you think about it, the car won't even be at full cooling mode until 215F and above.

So these cars run hot by design. My sisters 135i BMW did the same thing. Plenty of forum posts on that car too if I recall.

Woodman71

It's interesting, the highest coolant temp I have recorded on the 996 is 210 F, but my Mini hits 221 F on a regular day.

Volkert

So once you are sure the waterpump is OK, radiators are cleaned and the fans are running as they should the next suspect are the radiators themselves. I have seen other reports that only when changing them the cooling capacity was back to where it should be. When changing them it makes sense if you are willing to spend the extra $$ to go for the CSF radiators.

I observed the high fan kicked in at 107C, not 102C.

My car is currently having the fan-check + install of new waterpump and LTT. Got a call that the left fan did not kick in at low speed (it did do this at 107C at high speed) so this might explain why I was seeing it go all the way up to 107C).

Volkert

Remember the 996 measures and regulates cooling water temperature when entering the engine while typical is that this is done when exiting the engine. So your Mini might run cooler then your Porsche...

Mike Murphy

Good idea. I suspect that folks' fan and sensors might not be operating 100%. My 18-yr-old car, I suspect, doesn't kick in the low-speed fans unless the AC is on, indicating that somethings broken. I have yet to buy a Durametric, but looking for one.