dcsjc

Decided to tackle the coolant tank replacement yesterday on my 2004 C4S. Researched it ad naseum here and elsewhere and thought I knew all the tricks but it was still a bear to get out. In the process I heard a "crack!" and knew that the job just got bigger. It turns out that the AOS lower (corrugated) vent line on my engine is routed through the intake plenum between cylinders 1 and 2 and was blocking the movement of the tank. Even better: it was jammed right at the sharp-edge fitting on the tank for the coolant temp sensor. Well heck! Check out the carnage in the image below.

A new vent line (996 107 147 59) is arriving Tuesday and I found a nice DIY write up for the job in post #22 on this thread. This forum is great.

I plan to install the vent line first and then install the tank (seems like not enough room to install the line if I do it after the tank). I found some pictures on the net that show the vent line routed between cylinders 2 and 3, which is also where the above DIY says to route it. This should make getting the tank in easier and the routing between 1 and 2 is probably what made the tank removal so difficult.

If you guys have any more hints or tips, let me know!

dcsjc

Short update. Removed the old vent line today to get ready for the new one arriving Tuesday. It was so brittle that it came apart in pieces...

dan_189

That hose gets old moves around against the sensor in the coolant tank - same spot mine had a hole in as well.

If you have any questions let me know - it's a fairly straight forward job aside - access is tight though

dcsjc

Thanks, Dan. Getting the old hose out was straightforward. With the engine already lowered (for the coolant tank replacement) I was able to get my hand around the fitting on the AOS side to pull it off. That was the only tedious part.

When you replaced the hose did you route it between he intake runners for cyl’s 1 and 2 or cyl’s 2 and 3? I’m hoping that routing it between 1 and 2 will avoid the rubbing issue and also make the coolant tank easier to install.

808Bill

You might want to replace all the vacuum lines to. All that plastic is over due for a change.

Barn996

Nice bug-eye in your garage. What year and how long have you owned it? Hardly any room when I replaced the coolant tank in my '99.

dcsjc

Thanks! It's a 1959 with the 948cc engine, upgraded to ribcase transmission, front disc brakes, electronic ignition. Bought it about 4 years ago for our 20th wedding anniversary and my wife's 50th birthday. It gets driven on a weekly basis (Friday to work, over the hills to the coast on the weekends). It's funny how people in other cars and even pedestrians strike up a conversation with you at stoplights.

dcsjc

Thanks folks for the inputs. I finished job today. I like it when threads are tied off so here's the last bits.

I chose to reinstall the coolant tank BEFORE installing the new lower AOS vent line. I also used the trick mentioned elsewhere to remove the top black tank mount bracket. With no AOS vent hose, no black bracket and lowered engine the tank slid in like a breeze. Pushing the tank all the way to the back of the engine compartment (i.e. toward the rear seats) gave room to re-install the black bracket and then pull the tank forward and underneath to re-mount. Install was WAY easier than removal. I still hope I never have to do this job again.

Installing the lower AOS vent line was also straight forward, even with the coolant tank in place. It seems molded specifically to go through cylinders 5-6 and 1-2 with no obvious option to thread it any other way, so that's what I did. Getting it plugged onto the AOS was tedious until I figured out I could use my RIGHT arm with my body facing to the left of the car (armpit over the SAI pump). This gave the perfect angle to grip the end and push it onto the AOS.

Another useful tip from other threads was to use hose clamp pliers with the cable end. It made it very easy to get all of the hoses on and off.

Thanks for the suggestion Bill. I didn't end up doing this since I wasn't sure what parts to order and wanted to get the car back on the road. Since then I found this useful post from Ahasi that identifies all of the vacuum components:

https://rennlist.com/forums/996-foru...omponents.html

I tested the vacuum system with my mity-vac at the little black-white valve connection and it seems to be holding well so I'm good for the moment. But now that I know how to remove and replace the throttle body/plenum I'm ready for the vacuum lines whenever they break.

808Bill

Have you changed your AOS yet?

dcsjc

Yes about 4 or 5 yrs ago. So hoping I’m good for another 5+ yrs...