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After a nice ride, the engine is hot and nice, the fans are on (A/C off). Outside temperature is 77F but the temp gauge is reading too low. It starts too happen since this fall.
Temp sending and Temp II sensors were changed 2 years ago. Coolant changed last year and Red Line Water Wetter added.
Where did it sit before under those conditions? That looks about right in terms of the gauge position, compared to my car, although the lines don't have numbers corresponding to them on mine ('86.5).
if your auto vents dont close, you will run a lot cooler on the highway. on the race car, i have to put towels infront of the radiator to stop air flow so it runs normal temp (driving to the track in the morning when cool out)
My US '89 S4 gauge ran at exactly that point when it had the 75ºC thermostat in it. With the 85ºC thermostat, it sits a few needle-widths higher, still a couple needle-widths below the [assumed] 190ºF mark. IR readings at the water bridge outlet nozzle to the radiator confirm the gauge readings I have.
I'm not real clear on when the factory thermostat temps were changed from 75ºC to 85ºC. My car came to me (~20k mines on it) with the 85ºC thermostat. A 75ºC thermostat was supplied at it's first replacement at about 50k miles. At about 100k, the supplied replacement was 85ºC. Replacements were from our trusted vendors, installed during other normal services.
So where is the temp on an s4 supposed to be then?
I replaced my thermostat recently with an original part from porsche.
Which one? There are 75ºC and 85ºC thermostat versions available. Decide which one you installed, and read what I shared above.
The gauge sender is in the water bridge, as is the thermostat. The thermostat divides the coolant flow between radiator and recirculation based on the temperature it sees, and how it relates to the design temperature stamped on the thermostat itself.
If you don't already have one, you might consider adding at least a cheap IR thermometer to your tool collection. Use that to read the temperature at the right (right side is passenger side on US cars...) end of the water bridge where the hose to the top radiator port connects. The reading there should closely match the reading you see on the temp gauge, and hopefully the design temp of your thermostat.
To complicate things a tad, the WSM shares additional guidance, with a plus-or-minus ten degrees C hysteresis between full-open and full-divert thermostat positions. No 'integral' component included in the formula for the wax in the thermostat I guess. The hysteresis or maybe 'deadband' is what allows the gauge to walk up ten degrees C between low-load cold weather min radiator flow readings on the gauge, and high-load hot-as-hell service with the AC on in slow traffic. It's normal and to be expected.
On my 87 with an 89 cluster, the temperature gauge sits just below the 90 degree mark. It was sitting at the 80 degree mark until I cleaned the contacts at the pod and the grounds.
Thanks for your great comments.
It was a bit lower than the last white line in the similar situation.
I will take the cluster out, clean out all contacts and see.
"Which one? There are 75ºC and 85ºC thermostat versions available."
PET lists two thermostat options. One for cars up to 89 and one for cars from 90 onwards. I would have fitted the 90 onwards. Neither mentions temperature that I can see.
Perhaps one of the parts guru's can jump in with that info.
My original thermostat (12/88 build for 1989 MY) didn't have a number on it that I recall. But I do still have that part in the 'original parts removed' box if it becomes critical.
The 75ºC thermostat came from 928 Specialists, and was installed at the first coolant change I did after the car came to me in 1997. So would have been 1998/1999, sorry I'm not near the car or the logbook.
The latest thermostat came from Roger, and is the 85ºC version. My understanding is that this thermostat was fitted to the later cars, probably to improve emissions. The 'extra' ten degrees on the gauge doesn't bother me, and the better heater performance is a plus for a good part of the year since we moved from the Los Angeles area. The fans actually operate less on non-A/C days, with the slighly throttled flow through the radiator. In L.A., A/C might be needed on any driving day between New Years and Christmas. Bottom line, unless there's some other compelling reason to change, the 85ºC thermostat will be in the car for a while.
So what is your climate like, and do you use heat very often? In Los Angeles, average winter 'winter' high temp was about 70ºF, while average summer afternoon temp was closer to 90ºF. In a black 928 with no window tint, A/C was used most of the year. Now further north, average summer high temps are around 80ºF (guessing), with overnight lows from the 40's (early and late summer) to low 50's in late July and early August. So the heater gets used a lot, relative to air conditioning. In Los Angeles, I'd tie the heater valve closed for all but a month or two of the year. In the high desert climate of central Oregon, the heater might be needed on any day of the driving year.
The warmer thermostat, in conjunction with the [now re-activated] flaps in the nose, seem to help the engine warm up faster, and there's some more cabin heat available if needed. I put the car up for the winters because of the cinders used for snow and ice on the roads, but do still drive it until snow happens.
11-13-2015, 10:08 AM
Temp gauge reading too low??
