Blinking thermostat light?help

Ok guys I need some help. I am trying to troubleshoot, along with a Porsche tech, a blinking thermostat light. My car is a regular 99 cabriolet. 6 months ago I had a major service done to the car including the installation of an UAOS. within days of getting the car back on a drive it started blinking. I parked it and looked it up and it was a low coolant light. The coolant ok. And we double checked and bled the system to be safe. We even over filled it a bit per instructions on using the UAOS. early on if I just turned the car off and restarted it, the light would turn off. it was good for a few months. However, one morning the light came on at start up while it was cold. Again all the levels were good. Checked the coolant tank and the bobber seemed to be stuck, and it was freed. But that did not solve it. We checked the UAOS and it was fine too. we unplugged it and the sensor and it is still blinking. the coolant tank is new and not leaking. could it be a gremlin in the cluster? Any thoughts, similar experiences or solutions?

Quotes source post: 17879511

Hi I can help you with this as I know the system well. If you have unplugged the UAOS harness and the warning is still slow flashing, the issue is NOT in the UAOS. IF you have tested the Low Coolant Switch, and it is open circuit ( not closed), then the other thing that can cause the "slow flash" is the under hood temperature reaching over 150F. The DME monitors the underhood temp via a temp sensor mounted between intake runner 5 and runner 6. Make sure this sensor is mounted in the rubber grommet as designed and has not fell down on top of the crankcase. Also check the underhood fan to make sure it is not stuck with leaves/twigs. Finally if all has checked good, hook up Durametric or Equivalent and activate fan to make sure fan motor and relay are functioning and while monitoring underhood temp via temp sensor/Durametric.

Thank you. We have ruled out that it is the UAOS..it’s not the issue. it is not the under hood fan, that has been checked too. Would that under the hood temp be at 150 right as soon as you start it? I found an old thread and it makes me wonder if it is the coolant tank Spoiler I just found an old post, and I am wondering if it is the coolant tank. 

Quotes source post: 17879638

I remember that old TSB. I don't have access to TSB's anymore since I retired, but I remember that one. I was just commenting on another post about the changes that the Factory made in early 99's due to the coolant level control problems. I think this is probably the same time they implimented the "19 second delay" in the activation of the slow flash also. The underhood temp could be above 150F on a "hot start", but not on a "cold start". Also if it come on immediately on start , it probobaly not the "old tank design" but could be the "float" in the tank has "sank"... That can be confirmed by testing the Low Level Switch to see if it is closed or open. If the Low Level Switch is CLOSED with the reservoir full, then either the float has sank or the Low Level Switch is bad...

Thanks. I am checking on the open and close reply. We are wondering if something is wrong with the cluster. I have read people just drive with it blinking. It would drive me nuts, watching the slow blink.

Quotes source post: 17880437

The cluster could be bad, anything is possible but I highly doubt it.. There is only one wire coming from the cluster to activate the "slow flash" but it splits into three wires at the rear. If any of the three wires are grounded it activated the slow flash. The DME grounds one wire if the engine compartment fan system has a fault. The Low Coolant Switch grounds one wire if there is a fault in the Low Coolant circuit. The UAOS Sensor grounds one wire if there is a fault in the high oil accumulation circuit. You have to use the process of elimination to find out which circuit is grounding the instrument cluster wire, then trouble shoot that circuit. It can be simple or complicated, just have to use the correct process/fault tree steps and common since. I can guide you through the steps, but please don't confuse me by asking questions ahead of the next step..lol It has to be done methodically ..

We have checked everything and all the sensors are good. But I am still getting a random thermostat blinking light. Sometimes at cold start other times after running for a few minutes and sometimes it doesn’t come on at all. the system has been purged so it’s not air pockets. we have narrowed it down to the cluster. I did find some really old threads that the clusters would have issues, some got used to driving with it blinking. We are now trying to get our hands on an old cluster to swap and test it. Anyone else have this same issue?

IF the engine compartment temp exceeds 175F, the slow flash will also happen. I remember an old thread where a guy had the slow flash, and diagnosed it down to engine compartment temp circuit, and finally found the DME was grounding pin 82 all the time and causing the slow flash..

My notes show that speed of the flashing light can be a clue: "Four functions of the coolant warning light: 1. Engine coolant level too low -- light flashes slowly (0.5 Hz) 2. Engine compartment temperature too high -- light flashes slowly (0.5 Hz) (engine compartment blower might be faulty) 3. Engine coolant temperature too high -- light is lit; pointer on the right 4. Temperature sensor at water outlet faulty -- light flashes rapidly (1 Hz) ; pointer on the right Note: The temperature warning in point three is indicated if the conditions "engine coolant temperature too high" and "engine coolant level too low" are present simultaneously."

Thanks, we will give it a go..thanks for being more specific.

Quotes source post: 17928296

I also have 1999 with UAOS and have had on going problem with intermittent blinking low coolant light. I have been in touch with Porschetech3 and he sent me replacement UAOS harness but still had intermittent blinking low coolant light. If I unplugged the UAOS harness at the coolant sensor and plugged in the original harness the coolant light worked as it should (no blinking light). I only point this out to you to switch the harness before you go crazy pulling the dash apart. I have been in touch with Skip about this and he advised he will try and run through diagnostics to solve the problem but car is laid for winter so will address problem in the spring. Seems like the blinking low coolant light might be exclusive to the MY 1999, I think there have been other owners of 99�s with blinking low coolant light.

My 02 C2 had the blinking low coolant light after installing the UAOS. Since then Skip sent me a new harness that included a different sensor where it screws into the accumulator. Per his advice I filled the coolant tank to about an inch under the cap. My car is also laid up for the winter so it will be spring time before I can test the new harness. I have a new Porsche brand coolant tank, but used the original coolant tank sensor. As a data point, the low coolant light never blinked prior to the UAOS. Kudos to Skip for his excellent response time and help while a few of us sort out the issue. Also, one more data point, my friend's 99 has one of the first UAOS installed and hasn't had a single problem with it.

Quotes source post: 17929363

I agree Skip is a standup guy, very helpful and stands behind his product. Can�t wait for the UIDS. Like you my car wont be out of the garage until nicer weather, I have not tried filling coolant to a higher level, that will be one of the first things I try when car comes out of hiding. Thanks for that tip.