996 c2 1999 3.4 overheating issue

I can drive my car for happily 30 mins. Thermostat opens normally and will sit at 80 degrees c happily. Then after 30 or so mins. Temp Will slowly rise to 100. Fans cut in fine. None or little loss of coolant. Recently changed the header tank and cap due to a weep. Bleed the system by parking on a hill and revving for a few periods. Rads cleaned. Suspect a weep from rads What should I start with rad change, thermostat change. ? Anyone had anything similar ?

Have u pulled the front bumper and cleaned? Also grab a scanner that command the fans on at low and high speed to make sure both speeds r working. A bad low speed resistor can allow temps to rise.

Could be the water pump or air in the system. Try lifting the valve lever on the coolant tank and drive it like that for a day or so. If you don't know the age of the water pump I would replace it along with a low temp thermostat.

Are you sure you are overheating? If so, hopefully its just air in system as mentioned. But I could not solve my particular problem until I replaced coolant tank with a genuine porsche tank, turns out the cap just would not reliably hold pressure on the aftermarket tank (2). I followed the advice after install of driving with the valve "up" and topping off when cold for a few days. I had no idea at the time how old my water pump was and replaced for peace of mind. I am just a shadetree and replacing was not too difficult for me. I did the low temp thermo while I was at it. Good luck

Bookmarked 8/26/20 : Just noticed (1st time) a overheating problem in my 2000 C4 Cab. Temp gauge topped out in the red at 250 after just a short drive and I didn't even "get on it." Don't know how long i was driving w/it like that (just noticed it when I pulled into the driveway) but TG the engine didnt seize b4 I got home. Going to see if it needs any coolant after the engine cools down and take it out for another couple of short drives to see if it happens again. Noticed that the temp dropped while idling (but not that much) in the garage. Did hear a "hissing" sound near the coolant cap so maybe the tank needs to be replaced. Just hope it's not the pump which I'm sure will be very expensive to replace. --------------------------------------------------------------- Update 8/27/20 : Ok, I think I figured out what caused the overheating problem. Yesterday, I turned off the fan in the car because it was just blowing smoke from the local fires into my face. Well, I guess when you do that, it turns off the engine cooling fans too because when I drove the car today w/the fan ON, the temp gauge stayed between the 180 and next hash mark (210?) on the temp gauge and never went past the next hash mark after doing a variety of stop/go, back road and freeway driving. Who knew that you turn off the cooling fans when you turn off the fan inside the car? NEVER going to turn off the fan EVER again!!! --------------------------------------------------------------- PS: Now that I know that I don't have to worry about fixing the plumbing, I can go ahead and buy a set of Ferrodo DS2500 front brake pads and LNE spin on oil filter adapter pending the upcoming annual oil change.

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Many people think their car is getting too hot, but it�s fairly common to have a 911 (from the 1970s through the 2000s) that sits in traffic (or even at speeds under 40mph) to get well above the thermostat opening temps before the fans come on. But 100C is still not hot unless you are on the track (and on the track, we care more about oil temps than coolant temps). EDIT: ^^Let clarify the above comment^^ 100C in traffic is not bad since the engine internals aren�t very hot because the engine is generating 5-10HP. But on the track, the engine is generating hundreds of HPs, so the internals are hot. So the risk in damaging the engine due to heat in traffic is more related to a failed water pump, lack of coolant, or fan failure. The temp increases slowly with two of these failure methods. Unfortunately, a water pump failure might not show up on the temp gauge, which is why folks replace the water pump before it fails. My 996 dash temp gauge will go nearly to the very last white line before the low speed fans kick on, but DME temps reported from ODBII show it�s still between 96-102C. So if you are at 100C, that�s nice and warm, but not really a problem as far as I�m concerned. When to be worried: 1.) Your interrogated temps from Durametric or ODBII are higher than 102C. Don�t rely on the AC hack, as mine will show 117C when in fact the real temp was 102C. 2.) Your low speed fans - both of them - are not running when you press the AC button 3.) Your high speed fans never come on, even when it�s blistering outside and your AC is blasting (the high speed fans will come on if AC pressure is too high, a natural way to keep your engine cool). 4.) Your are smelling/losing coolant 5.) Your version 4 coolant cap (or coolant reservoir) is leaking 6.) Your temp gauge flashes red or points to the 250F marker Otherwise, it�s probably fine. The air cooled cars would also get hot in traffic. Reason: not enough airflow, plain and simple. Sure, cleaning the front radiators will probably reduce temps by a couple degrees and should be done once a year (every two years pulling the front bumper) by spraying a cleaning solution into the front bumper after hosing a cold radiator down with a jet hose (not a pressure washer).