Need some help troubleshooting

Symptoms...car began smelling like hot coolant. I found it had the old style expansion tank cap, and I saw crusting around the lip, so I replaced the cap. That seemed to take care of the problem. Then I had a set of PSS9 installed and soon after, began smelling coolant again. I wondered if the installation of the new coilovers had anything to do with it and was told that it shouldn't have, except that maybe the stiffer suspension triggered a crack in the expansion tank...a common problem with the 99 996's. After the install, for the first time, the car began overheating slightly...not a lot, but the needle would creep over the other side of the "O" where it never went before. I checked the expansion tank, and when I took off the cap, pressure escaped, so I assume that the tank is intact, otherwise it wouldn't have held the pressure....? Yes/no?? The tank was about empty...obviously leaking out somewhere, but there's no leaking on the garage floor, and I can't see dripping anywhere under the car. So at this point, I don't know what to focus on....if the tank holds pressure, could it still be the tank? Where would the coolant be going? I'd hate to replace the tank and find out that it's going somewhere else. I have checked the dipstick looking for water in the oil, and checked the expansion tank looking for oil in the water......everything seems in order. So I'm coming to the forum for some suggestions.

you need to pressure test it, with a pressure tester, coolant tanks usualy smell like coolant but often a small leak will never make it to the ground cuz it burns up on the exhaust. usually you can look at the exhuast on the drivers side and see evidence of coolant burning on the pipes and on the heat sheild. Other places to check is the water pump, the block off plate on the bellhousing side and the front radiators

Sounds like me a few months ago. These tanks crack all the time. On mine there must have been 5-6 cracks deep in the plastic starting and one that went right across a fold in the plastic and started to drip. It only leaked when the engine was hot for a while and i saw no coolant at all until a track day when i ran it hard. Even the next few day i got no drips at all just going to work and back. Check the drivers side exhaust tip for white crust of dried coolant. I though i saw the temperature gauge less stable before the change with it easily creeping up in stop and go traffic, and it "seems" much better now ive changed it out... could just be my imagination though :-) Perhaps the leak allows a little air into the system ? Good luck, its a DIY that isnt that bad really.

Sounds like the classic symptoms of a failing coolant tank. In the early stages it is likely that the coolant will never make it to the ground because of its location. Replace and forget. The temperature reading you experienced (just to right of the 0 on 180) is not unusual for the 996 (especially the 99-01 cars) under the right conditions. A slight lose of coolant would not cause this reading. More likely the light would flash on the coolant temperature gauge indicating low coolant well before you experience higher temperatures. As a side note: I would suggestion for you to periodically check the front radiators for obstructions. If you do a search you will find some great pictures of the amount of debris that can collect and block a portion of the radiators which can result in slightly higher operating temperatures. Twice a year I take off the front bumper and thoroughly clean out the debris in front of and between the radiators on each side. It is amazing what you find.

Brian: I did the search as you suggested and see what collects in the front radiators...I only have 25K miles on the car, so I don't know if stuff would collect that soon, but if you find junk in there in your semi annual checks, then it's likely that I would find debris in there as well. I just put some more water in the coolant tank...up to the max line, and took it for a hard drive. Temps stayed fairly stable until I got into stop and go traffic, then it inched up and over the "0", and I could smell a hint of coolant. I got home and took a bright spotlight and shined it down the left side in the area of the tank, and although I couldn't see any leaks or drips....below the tank I could see what looks like a layer of whitish piled up residue, sort of like cottage cheese ....which from other posts I've read, suggests a fractured tank with the telltale whitish coolant buildup. I found a replacement tank at Sunset for only $168, which was the best price I was able to find....unless someone knows of a better source?? My only question at this point is...why does the tank hold pressure if there's a crack in it? You would think that if the tank was cracked, the pressure would leak down as coolant was forced out. I've gone out and opened the coolant cap after the car has sat for 24hours, and heard the whoosh of pressure escaping. Bottom line is that it looks like a DIY coming up. Thanks for the feeback.

make sure its the right tank tanks for a 99 should be a lil more then 170 like 210ish

The cracks are pretty small really... like hairline Once i removed mine and inspected it quickly, i had a moment of panic as i thought i didnt have any cracks at all, and it was a cracked head or cylinder. ... once that passed i looked really closely and saw a few cracks, the give away was the white crud showing where the coolant leaked and dried on the tank. Even with the crack i lost almost no coolant and the tank level barely dropped at all.

Oh, Sunset had great prices... 99's are ~$200 like he said... 2001's are $76 ....guess i lucked out :-)

What?? 01's are only $76? I wonder what the difference in manufacturing is....probably that the 99's fail more often so they can get a better profit margin by selling more at a higher price? Not really, but I do wonder why the 99 tanks are almost four times the cost...when they're probably shaped about the same and use the same composition etc....yes...you did luck out. Wanna trade?

the 99 tank is diffrent becasue the sensor loads from the bottom (maybe the side one way or the other) and the 01 loads from the side

Chuck: depending on the driving conditions of your area there definitely could be accumulation of stuff in front of the radiators there after only 20k miles. My car is a daily driver and the area I live in has lots of trees resulting in leaves being a huge portion of the junk that collects in mine (along with small pieces of trash) and the main reason I do it semiannually. Since doing this the accumulation is not great but there is stuff in there blocking the lower 1 to 2 inches of the corner of the radiators.. Another thought on the temperature increase: The fact that your temperature just started going up in the stop and go traffic could indicate a plastic bag or something in radiators, or some type of failure of the fans. The air flow through the radiators is poor in traffic and/or slow speeds. There are fans behind the radiators that turn on to get airflow at slow speeds as temperatures increase. If the fans have failed or they are not running optimally this could cause the increased temperatures during traffic but explain while higher speed driving does not show the temperature increase. There are many threads on Rennlist and Renntech.org about testing the fans and/or even causing the fans to run at all times or to install a switch to activate the fans upon your command.

Brian: Thanks again for the suggestions. I will tear into the front bumper and take a look at the radiators there. Your plastic bag suggestion could be viable. I still get a hint of coolant...so I think that I'm going to order the replacement tank and have it on hand here as another DIY this winter when the weather keeps me indoors. I do hear the fans up front running when I come in to the garage before I shut down...so I assume that the issue of the fans not running is a moot one....unless that fan noise is attributable to something else....but neither my AC nor heater is running, so the fan noise must be the ones doing the radiator cooling. Thanks again for the feedback....it's really great to be able to get these sorts of helpful hints just by signing on and coming to Rennlist. I find I'm spending a lot of time here and on Pelican these days. Regards, Chuck