JFP IN PA

Very interesting information. You inadvertanly answered 2 sticky questions I was trying diplomatically compose. so moot now. At this quick moment I have, I can recall two comparatively softball questions.

1) As I understand from you and maybe others on this thread, Porsche concocted this whole charade so they could burn up more oil with the extra heat. I thought it was for emission issues but, if it blows out the pipe it's going to hurt not help in this arena(No?) is it blow-by?

Or, Could it be just to mitigate that early morning start-up cloud syndrome that some people have and freak out about? In which case, no matter for me, it would be long gone by the time you get to the smog station.

Tell me they did not do this to try to keep the outside the motor cleaner> avoid build up to...keep the motor running cool? (To ironic)

Thanks as always, gotta run...

PK

Is blow by that going to become aprent or

The use of higher coolant temperatures is done purely for emissions purposes. Running the cooling system at very high temps has been a crutch used by the OEM’s since the late 1960’s when everyone ran carburetors. Running hot helps nearly any engine reduce emissions with the poorly controlled fuel delivery systems that existed at the time. Unfortunately, even though modern injected and ECU controlled systems do not need to run that hot, the band aid has persisted because it also helps extend the cat converter life, and as the cat is covered by the federally mandated 80,000 mile operational life warranty, they will do anything to prevent having to replace the cats.

Interestingly, jacking up the coolant temperatures also lowers the volumetric efficiency and increases the chances for fuel flame front propagation issues (knock, detonation, etc.), so decreases in ignition timing are needed when the engine runs hotter. Net result is poorer performance, worse fuel economy and shortened oil life.

As for coolant temps allowing the oil to “bun off” contaminants; that rationale has always been somewhat suspect as the oil always runs hotter than the coolant anyway, plus the two main contaminants (water and fuel) would still flash off at lower temperatures as well, so lowering the coolant temp 20-30 F should not be a factor.

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I realized that I do have a scan tool that is capable of communicating with the DME in SAE J1978 "Generic scan tool" mode. One of the data lines available in the Generic scan tool mode is ECT, so off I went to compare temp gauge readings, HVAC diagnostic mode coolant temp readings and scan tool ECT readings.

Key on, engine off:
HVAC = 31 deg C (88 deg F), Scan Tool = 91 deg F

Gauge needle exactly on the "tic" above the "8" in "180':
HVAC = 78 deg C (172 deg F), Tool = 181 deg F

10 miles on highway at 75 mph indicated, 83 deg F ambient temp & gauge needle straight up between "8" and "0":
HVAC = 91 deg C (196 deg F), Tool = 194 deg F

Idling:
HVAC = 100 deg C (212 deg F), Tool = 208 deg F
HVAC = 101 deg C (214 deg F), Tool = 210 deg F
HVAC = 102 deg C (216 deg F), Tool = 212 deg F (gauge needle near right edge of "0" in the "180" label)

Given these results, I can only conclude that (on my car, anyway) the HVAC panel diagnostic mode is reasonably accurate at typical cruise temps, and that when the gauge needle is "straight up" between the "8" and the "0" my coolant temp is 190 - 195 deg F. It is a bit odd that the HVAC diagnostic display ECT is cooler than the scan tool displayed ECT until approximately 190 degrees F coolant temp, then the situation reverses -- the HVAC display reads slightly higher than the scan tool reported ECT. The Bentley manual hints that the HVAC panel receives engine coolant temp from the instrument cluster, so maybe the cluster is re-scaling the ECT data to effect a slight change...or maybe not.

These results make a lot of sense to me, because a 10-11 degree C (18-20 deg F) coolant temperature gain through the engine is quite plausible under the conditions noted above. If the inlet side thermostat is 80 deg C, and the coolant exiting the engine is 90-91 deg C, then I'm quite happy with that.

BTW -- I noticed an anomaly: at highway speed, my cluster was showing 83 deg F ambient air temp but my Intake Air Temp (on the scan tool) was showing 66 deg F! Maybe this gives me a wee bit more spark advance than I otherwise would have...

Based upon the 986/987 wiring schematics, I would have suspected that would be the case, which unfortunately means that the inaccuracy and non linearity of the dash gauge is transposed onto the HVAC display. Standard diagnostics for faulty dash displays always start with measuring the same data via the OBD II port, which is an indication that the port sees the sensors directly without the influence of the dash display. This is why I tend to trust my diagnostic instrumentation over what the dash is telling me…………….

"BTW -- I noticed an anomaly: at highway speed, my cluster was showing 83 deg F ambient air temp but my Intake Air Temp (on the scan tool) was showing 66 deg F! Maybe this gives me a wee bit more spark advance than I otherwise would have..."

Be aware that these measurements come from two different places, one is in the front grill, the other is inside the MAF; so cooling effects of the relative air movement as well as exposure to ambient sunlight are different…….

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Yeah, I knew that the cluster's ambient temp sensor was in the grille area and I was pretty sure that the IAT was built into the MAF sensor. I was doing my test driving at 10:30 at night, so sunlight wouldn't have been a factor. I had the top down for my test drive (why not?) and the air temp definitely felt a lot more like 83 deg F than 66 deg F. I'm not particularly worried about the low IAT reading, though. Everything else that I could see looked good -- LTFT on both banks was +1 to +3% and STFT was bouncing +/- 2 around zero. I even found that my radiator fans DO work on high speed with the A/C on, so my only fan issue appears to be an inoperative left low speed fan. It was a good test drive...

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JPF and Blue_ s ("s"for "sleuth"?)

Good job. What a plot twist, What a surprise! (not).

Aren't all these sensors O to5 v? and gauges the same? If so, with schematics, pretty simple measurement; sensor to tach and from tach to hvac, although it might easier said than done, that instrument cluster is just about every but, mainly one big circuit board is more like it

Anyways, if you wanted, it would seem like an easy hack to jump your way around the gauge.

Anyways, with an obcII reader, it makes all of this moot I, but it would be nice to accurate look at the dash and get an accurate read, and worst fumble with the hvac.

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I just couldn't resist gathering more ECT data over the weekend:

80 mph in the cluster, 96 deg F ambient temp in the cluster
HVAC = 93 deg C (199 deg F), Scan Tool ECT = 196 deg F

The highest ECT I saw in 40 miles of driving was 201 deg F on the scan tool, and that was at 75mph in a 98 deg F ambient temp, while climbing a shallow grade. Still, I will probably install a 160 deg F thermostat the next time I have an excuse to open the cooling system. I'm just not eager to replace a year-old stock thermostat right now...

Good work Blue-s, Keep it coming, Now try it at 110 (kidding of course), seriously though good work. So the upshot is despite all the hankpanky in the gauge, we can trust an OBCII scanner and the HVAC readout..more or less? You sound like you don't necessarily buy into the 160 ?

My numbers: I would say that you temps are the highest (outside of the track) actually is sitting in traffic, In my experience, ya got nothin blowing throught your rads. I could use that for an excuse for doing my testing in the drive way at 0mph, but I was just lazy and wanted to see the hvac thing work. Forget I forget If I posted this but:

Idle.....needle to the left of 180.............hvac....200......normal cruising needle position
Idle.....needle over rt end of 180...........hnac....210......fans come on

Give me a spiel, talk me in or out this, I'm in no hurry to dig into the cooling styem either. But my motor takes a beating. Was there the 5HP.increase claim (yawn)? Is your take on your scanner it's just not so significant enough?
Regards, PK