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955/957/958 Cayenne DIY: Fixing the coolant manifold fitting with a threaded adaptor


955/957/958 Cayenne DIY: Fixing the coolant manifold fitting with a threaded adaptor

Old 01-30-2018, 01:03 AM
Thread Starter
Join Date: Mar 2017
Posts: 8
Default 955/957/958 Cayenne DIY: Fixing the coolant manifold fitting with a threaded adaptor

This thread will show you in detail with pics how to repair your coolant manifold in the back of the engine where the hose fitting is coming unglued and u will end up with sudden cooland loss and eventual engine failure or be stranded in the middle of nowhere. Bottom line this is an issue that all 4.8L owners should address sooner than later.

My car started loosing coolant more and more but there was no sign of it under the car. Few months later and about 4 quarts of coolant toping the coolant made its way down onto the driveway so I decided to dive into it . After reading a few posts I realized that the leak will be either from water pump, thermostat housing, thermostat intake o rings, plastic pipe under fuel rail or failed coolant manifold fitting. Time to replace all , car has 100k miles so it will be a perfect time to update all.

After I removed the intake manifold there was coolant into the valley of the engine block. I will not go into detail on how to remove the parts to get there.

You can see the reddish coolant pooled in the valley of the engine.

Next I removed the water pump, thermostat intake and housing and lower pipe which is the plastic pipe that's under the fuel rail. That pipe is a pain to remove since it will not come out from the thermostat housing. Also I will replace the double plastic vent pipe.

You can clearly see the plastic pipe, vent pipe and the manifold in the back that will get to .

After a closer look my leak was from the thermostat intake orings or around that area. After digging so much into the engine I had to check the fitting in question on the coolant manifold. You will have to remove your hp fuel pump in the back of the engine on DFI engines . The fitting is right under it .

Without removing the pump you will not be able to see the fitting or to work on it . Some of the screws holding the pump are very dificult to remove.

After removing the hp fuel pump and taking a closer look my fitting looked ok and not moving at all, hose was all the way close to the manifold with no signs of getting loose. So what now? I didnt want to leave it like that since it was a ticking time bomb so I decided to drill a hole from the top tru the manifold and fitting , tap it and install a set screw like other did here on the forum but that was done under the car with trans removed . Just so clarify there is more than enough space to drill and tap from the top. It wont be easy but with little patience it can be done.

I went and got a 1/4 - 20 tap and drill set from the hardware store and drilled and tapped the manifold . To remove the chips I removed the clamp holding the hose onto the fitting , by the way u will need a clamp removal tool to get behind there. Craftsman makes one.

After removing the clamp I started pulling on the hose to remove it so I can use a vacuum to clear all the chips from the drilling and taping.

GUESS WHAT ??? The moment I pulled on the hose the fitting and hose pulled right out of the manifold with very little effort.

It took me a while o get that fitting out of the hose but got it done .

This is the infamous fitting that everybody is talking about.

Cayenne_turbo is offline  
Old 01-30-2018, 03:46 AM
Thread Starter
Join Date: Mar 2017
Posts: 8

After a few measurments and contemplating ways to fix this issue it seemed logical to me that the only way to fix it is with a threaded adaptor and NOT USING SAME METHOD USED BY THE FACTORY.

The OD of the fitting and ID of the manifold are 18mm, so I checked the next size thread available and that is 20 mm.

20 mm thread comes in pitch 1, 1.5 and 2.5 , 1 is too fine and 2.5 too coarse so I opted for 1.5.

Also 20mm 1.5 pitch requires an 18.4 mm hole for threading which was pretty close to my 18mm.

Next I ordered a 20mm x 1.5 thread starting tap and a 20mm x 1.5 bottom tap. Got these from McMaster-Carr you can shop around for better pricing.

The thread starting tap has about 7 threads that are tapered so you can easily start the tread and it also will keep your tap centered.

When done threading with the thread starting tap I switched to the bottom tap to finish the thread all the way to the bottom of the hole inside the manifold.

I used a 15mm ratcheting wrench on the square head of the taps and went very slow in the beginning until I was centered and started the thread.

I also got a 20mm x 1.5 die and a handle for the die . I looked all over the net for a 20mm x 1.5 to barb adaptor with very little luck so I decided to make my own. Also material was key too since aluminum dont like brass or stainless so it had to be aluminum. The next size up from the 20mm was 7/8" so I got a 7/8" T6061 aluminum hex stock .

All of these will run you about $225 at McMaster-Carr. Did some measurments again and started making the adaptor.

I used my lathe to get the part done . I tried to match as much as I could the original specs. The new piece ended up longer since it has a hex for wrench.

You will have to find a machine shop to make this for you if you dont have access to one .

Next I used some teflon tape and installed it into the manifold . In the picture u will see that I used a set screw to fill the hole I originaly drilled but later changed my mind due to stainless and aluminum and decided to epoxy the hole.

This is how it looks after the hose was installed and hole was jb welded.

The hole had threads from the 1/4 - 20 tap so the jb weld had something to grab into.

Hopefully this will help others out there trying to find a permanent solution to this problem.

I'm still waiting on parts to finish up the rest of the job and I will post more when I'm done putting all the cooling parts back and do a pressure test.
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