Project 718 Cayman T: Part 9 – GT4 Undertray Vanes and Water Pump Mod

There are many valves which depend on vacuum signal lines to actuate; blow-off valve, wastegate, engine mounts, exhaust valve, and numerous coolant valves used to regulate coolant and oil temperatures off the top of my head. The 991.2 Carrera is notorious for coolant pump failures where the coolant gets sucked deep into the spiderweb of vacuum lines. Once that happens, everything connected to a vacuum line is suspect. During a water pump replacement on a 991.2, it is also mandatory to replace the Change Over Valve Assembly which is an assembly of 6 valves that control which items get vacuum signal. Yeah, I want to avoid any future headaches related to coolant clogging up the vacuum system.

Getting to the pump means going through the bulkhead opening behind the seats. I was going to remove the passenger seat, but the fasteners are some spline head like on the rear brake calipers. Of course, it wasn’t the same size as the head size on the rear caliper, but some size smaller. I managed to do this job with the seat in place.

What I thought was an access panel on the bulkhead panel turned out to be fasteners to hold a mass damper. I’d guesstimate the damper had a mass of about 5 lbs. I do wonder what potential buzzing noises would occur with the mass removed.

I got this dowel pin from Mcmaster to use as a plug in the vacuum line. 18-8 stainless steel to be corrosion resistant, 6mm diameter to jam into the 5mm inner diameter hose, and chamfered edges to make it easier to install the plug into the hose.

That little black vacuum line hiding behind the belt is the one I need to get to. I’m sure this job would have been easier with the belt out of the way, but I didn’t have the correct size hex socket for the belt tensioner. I managed to push the hose off by getting a flathead screwdriver under the end of the hose. Just pulling on the hose will not work because it causes to hose to stretch and grip the hose barb even tighter; it’s like a Chinese finger trap.

It was tricky getting the plug installed as I had very little space to work with. There’s just not much space for two hands in this area and the hose is short, so you can’t pull it out to an area with more space. Typically, I would have used some lube to make it easier to install the plug, but I couldn’t risk dropping the plug and potentially losing it forever into the abyss of the engine bay. I used the same coat hanger from the front bumper job to help fish this vacuum line. Also, no signs of crustry coolant residue in the vacuum line or the hose barb on the coolant pump after almost 4000 miles. Yes, some water pumps have failed that quickly.

I was only able to push the vacuum line this far back onto the hose barb which pushed the plug into the line about 3mm-4mm. I probably tried to push the line over the barb for about 15 minutes which also meant pushing the plug in further. Maybe it was a half hour. Either way, I was into the job about 2.5 hours at this point and decided to just go get a cover for the hose barb on the water pump.

After a trip to Autozone, I put this rubber cover over the hose barb on the pump. I then jammed the vacuum line with the plug between the rubber cover and the aluminum block. I don’t foresee anything moving around.

Are the GT4 air turning vanes a worthwhile modification? That’s a good question. I think it’ll incrementally improve the intercooler performance, but I haven’t tested that theory and I have other things in the works where I won’t have a proper A to B test. If you care about rock chips on your rocker panels, the air turning vanes may be a contributor, but those may have just been a coincidence. If you’re looking to eek out every bit of performance for the track, then I would say to go for it. If your car is more of just a fun street car, then I wouldn’t bother. With the water pump vacuum line plugged up, I no longer have to worry about sucking coolant into the vacuum line spaghetti and clogging everything up. Worst case if the seals in the pump fail, coolant will seep out from under the cover on the hose barb and drip onto the ground. That scenario is much preferable compared to contaminating the vacuum line system. A nice benefit of this water pump mod for me is that I can now start the car in Normal mode without actuating the shutter which will probably make my neighbors a little bit less annoyed due to the quieter exhaust. Another observation after oil change number four at 3714 miles: the oil came out less shimmery. So it feels like the engine is well broken-in now. I know, it’s not a scientific metric. Oh yeah, go ahead and screw in those GT4 scoops.