How to use a S4 (1986-1988) aluminum water pump housing on a first gen (1979-1985) 12
 

How to use a S4 (1986-1988) aluminum water pump housing on a first gen (1979-1985) 12A

Parts:
1. S4 1986-1988 Water Pump Housing
2. S4 Water Pump and Gasket
3. S4 Water Pump Pulley
4. S4 Air pump bracket – if an air pump is installed
5. 12A Water Pump Neck

Tools:
1. M18x.1.50 Tap
2. M8x1.25 Perma-Coils
3. M8x1.25 Plug
4. High temp sealer

1. Obtain 1986-1988 S4 aluminum water pump housing. This can be turbo or non-turbo. A S5 will NOT work.

2. I used stainless steel bolts/nuts but they are not required. They are expensive but are nice because they do not rust and will not cause issues with the aluminum.

3. Remove the large sensor from the rear.

4. Tapped the large sensor opening to M18x1.50. This will be used for the 12A factory water temp sensor used for the choke. You don’t need an expensive tap. Your only tapping soft aluminum.

5. The location of the rear nipple is where I tapped for a 1/8 NPT water temp sensor. I like electrical gauges for the ease.

Use a pair of pliers and turn the rear nipple to free it up. Do not bend it. It should turn but if it is stuck, don’t worry. The nipple can be cut and drilled out or a small screwdriver placed between the nipple and housing to deform the nipple. Don’t go crazy and take your time.

6. There is one less long water pump engine stud on the 12A vs the S4. To overcome this, I used a Perma-Coil (Heli-Coil) on both ends the water pump housing. The size is M8x.125 to be the same as the stub. The rear Perma-Coil gets a M8x1.25 plug.

https://cimg8.ibsrv.net/gimg/www.rx7...8dd20b5dba.jpg

https://cimg7.ibsrv.net/gimg/www.rx7...02e5e58c0e.jpg

https://cimg3.ibsrv.net/gimg/www.rx7...983a25a8cd.jpg

https://cimg9.ibsrv.net/gimg/www.rx7...a26d09788e.jpg

I media blasted and powder coated all my parts. This is not required but sure looks nice.

https://cimg6.ibsrv.net/gimg/www.rx7...dfd293eec3.jpg

NOTE: If doing this for a 1984-1985 GSL-SE 13B, do not remove the rear nipple.

Looks Good!

Thx for the comments. Can't wait to get this thing back into the car. Just have the intake, carb and engine bay to cleanup before it goes back in.

This is an awesome thread! I vote for an archive with this one since it's well-written, thought out, has good pictures and will be easy for people to understand :bigthumb:

What's the benefit of this change? Better flow rate? Parts unavailable for SALE? Just curious, as I know theres probably an extra 5-7lbs on the cast iron pump housinget vs. aluminum.

Primarily weight savings.

Weight saving is the main reason. I like the ability to more easily add a water temp sensor.