Cold running 996?

My 2000 C4 has been acting up lately. Staying cold for a long time 30 minutes in stop & go traffic and still only showing 140 +/ temp. Then the Check light comes on after a few days of this with a P0115 code. "Coolant System". So we replace the Temp sensor... and it is OK for two days. And it starts again - I now also note that both cooling fans are ON - all the time - but no CEL. Back to Chris's we go and it is intermittent... works for them, so we drive off and it is OK till the second start and Pop comes the CEL and it stays at 140f & fans are on full when I pull in the garage. Let it sit a day check the CEL and it is again P0115 and the fans come on when I start the C4. So any thoughts - Chris thought the Thermostat might be acting up but the CEL 115 says Temp Sensor again and I do not think the Fans would go on if the T-Stat was full open and running cold???

funny the fans are on. I wonder if the water pump is not circluating the water and you have hot and cold spots? I thought that right out of the gate when I saw you but didnt want to undermind the diagnostics that had been done with an off the cuff remark.... I will ask Jason tomorrow what his thoughts are and lets see what the group here comes up with. Great to see you Jack

30 minutes of stop and go traffic without coolant circulation I'd think would kill/make the engine konk out being hot with low rpm's. But I have seen tv commercials of synthetic oils......yah right. Could be the fans on are keeping the temp down. Whats the outside air temprature? Could also be another owner did a fans hack plus took the thermostat out. So if it is cold weather then I could understand the car running cooler. Yah just checked Seattle weather online and its time to evacuate Washington state. What the heck are you guys doing to the weather over there? It's supposed to be global warming. Not knowing the variables the ECU is watching but possibly the car not coming up to temp is what sets off the sensor is bad error. The thermostat being out is what I'd first suspect along with a fan hack. Then I'd also check for a loose connection by wiggling and unplugging and plugging stuff back in like sensor wire and ecu related stuff.

I would check the thermostat, one stuck open could cause the low temperature readings. Is there a separate temperature sender for the gauge and the DME? Rick 99 996C4 87 944S

open thermostat would be the cold water suspect - but why are the fans running, do they run when the defroster is on? - Jack says they run ALL THE TIME>? maybe separate issue? do the fans normally run on start up like tha aux pump (I forget - been a while)

Don't the fans come on 100% when the AC is on? Maybe a failed sensor/switch for that circuit.

running cool is weird, I was under the impression even with a full open thermo, the engine woudl still heat up fast, Thus the big argument I got when I installed Jakes lower thremo. I dont think its running cool. I think you have a sensor issue somewhere.

Are the radiators warm or cold? If they're hot and your temperature gauge isn't registering it you can focus your attention on the temperature sensor. If they're cold despite plenty of warm up time you can focus on the thermostat.

There is no "Hack" issue here as the car has run 3000 miles without an issue in both hot 80f and cold 40f degree weather since purchase. My guess is that the fans on full all the time simply reduce the temp in today's weather to 140f operating temp rather than the 180f the car normally has been running. Add to that the fact that the boys a Chris's spent a few hours looking over all the wiring to the front fans, checking resistors, etc. So far it stumps them, and the intermittent nature makes their task very difficult. One ( I hope not $$$ ) option is that the DME is going nuts? I thinks the engine is Hot when it is cold so it is turning the fans on. Or the DME is in a Fail-Safe mode that says - "I cannot tell what the engine temp is 'Cuase my sensor input readings are goofy - so I will over-ride and protect my motor by putting the fans on full." ??? Or the new Temp Sensor installed last week has failed? and we just need to replace it again? If the Thermostat was stuck open...slowing the warm up - the symptom would be the same - except I cannot understand why the Fans are on.

I'd watch and see if the oil pressure is giving signs of engine oil temp. Do you go down to 1 bar or what ever the usual pressure is or remain up around 3 or so after a usual warm up period. This is to figure if the engine is actually heated up to operating temp or not. Like you figure it could be an intermitent, dirty contact/'s or faulty equipment. God luck.

I would be surprised if the DME was "nuts" has anyone had to replace one ? (have not heard of any, not that it doesnt happen)

There is no "Hack" issue here as the car has run 3000 miles without an issue in both hot 80f and cold 40f degree weather since purchase. My guess is that the fans on full all the time simply reduce the temp in today's weather to 140f operating temp rather than the 180f the car normally has been running. Add to that the fact that the boys a Chris's spent a few hours looking over all the wiring to the front fans, checking resistors, etc. So far it stumps them and the intermittent nature make their task very difficult. One ( I hope not $$$) option is that the DME is going nuts? It thinks the engine is Hot when it is cold turning the fans on. Or the DME is in a Fail-Safe mode that says - "I cannot tell what the engine temp is 'Cuase my sensor input readings are goofy - so I will over-ride and protect my motor by putting the fans on full." ??? If the Thermostat was stuck open - the car would run cold - but the fans would not be running ???

Well ... Here is "the rest of the story" Got my new thermostat and water pump from Sunset sent to Chris's and today they went in to see if the Thermostat was in fact stuck open. Well it was as OPEN as you can get - It was Not there! Apparently a Prior owner either had an over heating issue... or tacked the car and wanted it to run cooler ...or something (?) and simply removed the dam thing. Even broke off the inner tabs on the Housing, so we had to put a new one in as well. I know it gets warm in Riverside County - but this does not make sense to me. All appears to be working fine now - But why do this??? Anyone have a thought?

Could be he only drove the car in summer and just putted in town where the car would heat up more than his liking. It is a common practice of the old days to just take the thermostat out so that the engine runs cooler. Could be the car was tracked with just water since some tracks only allow water or water with water wetter or whatever that stuff is. Part of the old thinking which I think is still a good reason is taking the thermostat out prevents the thing from freezing up on you leaving your car engine toasting. Maybe he couldn't afford a thermostat. Maybe the car used to have a bunch of garbage in the radiators over heating the car and after removing the thermostat he figured out cleaning the radiators. Runs good now I hope.

Hey, Great news Jack... what a surprise to see me again hey I guess in my #5 post I thought the T-Stat was the issue but could not figure the fans, did the new T-Stat resolve the fans too? See you later this a.m. for your "burping"

Glad that you found the issue. Sorry about the damage the PO inflicted. Wish I had seen this earlier. That's exactly what I did with my 951, with identical results - perfect temperature in the summer and 140 to 150F in the fall and spring (although, my fans only ran when the engine reached the temperatures required to bring them on).

Yes the C4 ran great coming up from LA and on a long trip to BC - all in relatively warm summer weather. Then comes a NW cold spell with temps in the low 30's and I have a problem. First indication was the CEL - so I guess that low temp - about 140f was not good for the DME. I must admit I confused myself on the fans. In these C4's with Tip the low speed fans are always on if the A/C is on - an unlike my Audi the A/C will come on in cold temps. The Audi will not allow A/C below 35f. So the fans worked OK. All seems well today. Drive home last night in 50f weather and 35 minutes of stop & Go traffic the engine temp was right on the 0 in 180. This morning we had heat in 1 mile and full temp to 180 in 2 miles and then it just sat there like it should. Engine is perrrring and I am Happy - and just a bit Poorer ;-) Now I am wondering what else was modified? Is the DME a TechArt box? I'LL have to take a look!

LOL - dont fix anything that is working Glad your up and running - like you I wasnt sure when the fans come on. I had wired my fans to run on high when they should be on low....I like the sound of getting ready for take-off!! You should be set now a the next couple years on just oil and gas.....See you soon!!