MaxPower2000

Hi all,

I’ve been lurking on the site since November, when I picked up a 1989 S4. I had it in for a big service in the spring and it’s been a light daily driver for the last month. We’ve had a wonderful honeymoon, but now there’s signs of trouble in paradise. I’ve scoured this forum repeatedly, as well as other sites.

In the ~1500km since I’ve had the car the temperature needle has fairly consistently levelled out at about 2mm below the line separating “center field” from “right field”. I’ve interpreted this as ok! Problem is, on occasion (not always) I’ve been getting the flashing “Engine Temp. Too High” warning on the information display (>=120C), and the warning light beside the needle gauge comes on at the same time. Note that in the hottest scenario (slow traffic, ~27C ambient), the needle still only just got to the right field line. Never into right field. I also never get the non-flashing warning (>=118C), always straight to the flashing warning.

In my testing, on cool mornings, I have no issues, no warning message. Warm afternoons with slower traffic, I will usually get the warning. Starting the car after it hasn’t fully cooled down for a few hours, I’ll pretty much always get the high temp warning.

After getting the warning, I’ll check temps with an IR temp gun. Radiator hose of the left side (when standing in front of the car) very typically reads about 89-91C…. the right side about 78-82C. As memory serves.

More details:
— Flaps safety wired to 100% open
— Both fans functional. Run when AC is pressed. I’ve also observed them cycling on and then off when the temps are in the ranges described above.
— Oil still looks new
— New thermostat installed at recent service
— Wildcard: the fuel gauge will sometimes not move on start-up.

Questions:
— The temperature readings and fan behaviour seems to line up with the function charts in the WSM. Can it be assumed the cooling system is functional (minus the flaps) and this is possibly a sender/sensor error? (The disagreement between needle and warning screen is confusing then)
— Where does the information display and needle each get their info from? Based on the WSM and wiring diagram, is it orange/brown device on the water bridge in the photos? What is the blue one?

Finally, this little blurb from the owner’s manual seems pertinent… “Should a component fail, the coolant temperature warning light gives indication of excessively high coolant temperatures and a fault message appears in the information system display.” Could this message be a result of the flaps being wired open? Very odd as it was done by a PO and the message would have presumably been there for them.

Sorry for long post. Anyway thanks for any advice.

—Chad

Gretch

Who modded it?

I have no recollection of it..............

Mark in Baltimore

Don't recall seeing it.

John Speake

The sensor with the blue plug is a double temp sensor for the engine electronics. The brown one is the one that is fed to the dash.

Was the small seal behind the thermostat changed ?

MainePorsche

When you say 'flaps wired open', do you mean physically wired open ? A better way to keep them open is to pull the fuse for them, and then physically turn the **** atop the motor to keep them open. If this is the case, I'm just wondering if current is still be fed to the flap motor and if wired in a fixed position, this would be sensed as a component failure and hence the warning (?). I'm not that familiar with the intricacies of digital dash warnings.

dr bob

The flap position has no direct effect on the digital display. Common methods for keeping the flaps open start with MainePorsche's recommendation to just pull the fuse for them with the key off. "wiring them open" is not necessary. Pulling the electrical connector for the flap motor exposes the terminals to moisture, so is not recommended.

Whe we moved to a cooler climate (Los Angeles to central Oregon) a few years ago, I put the fuse for the flap motor back in to restore its intended function: warm the engine faster. Gives much faster cabin heat too on cold mornings.

For your reported symptoms, I'd start with the easy step of disconnecting the sender and cleaning the connections on it. The common recommendation is a product called Deoxit, sprayed on the pins and into the connector. You should do the other sender at the same time, the one that feeds the injection and ignition controllers. The one that feeds the dash display need only a momentary connection glitch to generate the warning and light. If the engine has been serviced including painting or powder-coating that water bridge, the bridge itself may not be securely grounded. That would also give you the erratic signal to the dash display.

Under the pod there are (IIRC) three connectors. Take each one off and back on a few times to scrub any oxidation off the board and the pins. DeOxit there is a good idea. Do these one by one so you don't get them mixed up.

soontobered84

When I was getting this warning, and after I determined that my engine was actually not getting too hot, I thought it was the sensor gone bad. In reality, my engine harness was getting chewed up by the accessory belts and the harmonic balancer, etc. I never heard a funny noise or anything else strange until the chewing got into and through the main power cable about 10pm one night.

It shut the car down.

I got a new engine harness from Sean. It made all the difference.

Hopefully, that is NOT the problem you are having.

MainePorsche

I just wondered in the latter S4 with digital warnings with the data above from the owners manual, if the flap control (which is controlled by the fan control module) is generating a 'component failure' signal by having the motor potentially straining against the wired flaps.

SeanR

Seen this a few times and each time it's due to a bad engine wiring harness. You can get them through Roger @928sRus and he can fix you up. I know he's got one on hand ready to ship.

MaxPower2000

I believe the seals were all changed, but that's just based on the notes from the service record and materials listed. Not certain about that specific one.

The flaps are physically held open with wire, and on closer inspection, the linkage between the motor and the flaps has been removed, so no straining. The fuse is intact. I wish I could find more info on the internal logic behind the "component failure" mentioned in the manual, but it seems like as soon as the wiring hits a control module, it's a dead-end for me.

Driving home yesterday, I paid a little more attention to some of the other dash readings. I previously mentioned the fuel gauge will sometimes not work on start-up. That has continued, and on at least one occasion, it started working randomly during driving. I also switched the display to the ambient temp setting. As I drove, the ambient temp reading climbed steadily, reaching 35C.... MUCH higher than the actual temp of about 20C.

Per the WD, these devices all share a common 'signal ground', so maybe there's a common issue closer to the pod end. (To keep things interesting, the oil pressure sender also shares this ground, but seems fine as far as I can tell.)

In any case, I'm hoping to find time tomorrow to walk through and clean all the contacts involved. And also hoping it's not a bad harness.

MaxPower2000

Brief update: I've only managed to clean the sender contacts, no change. The high engine temp alarm, and the high ambient temperature reading still happen concurrently. But I've found that a stiff whack on the pod will temporarily clear the alarm and restore the outside temp reading to a more reasonable number.

Looks like I need to remove the pod and clean up the instrument cluster connectors next.

dr bob

No need to remove the pod to do a DeOxit cleaning.