Engine Cooling

Coolant Reservoir Hose Replacment

People:

Recently, I replaced all of the coolant hoses on my '82 Weissach 928 (928 S). The most difficult part of the process was replacing the j-hose under the coolant reservoir.

Since the J-hose for the reservoir is connected in the right rear corner of the underside of the coolant reservoir, you'll need to be able to invert the coolant reservoir to replace the hose.

To replace the j-hose (or replace the coolant reservoir), you'll need to remove the diverter valve for your emissions system to get clearance to invert the reservoir. The diverter valve sits on top of the RH valve cover, approximately between the spark plugs for cylinders 3 and 4. There are four lines leading to the diverter valve. The rightmost is a cloth-covered hose for vacuum, the one closest to the firewall is an intake bypass to the airbox cover, the one closest to the center of the engine leads to the catalytic converter and the most forward leads to the air pump, via a stepped, ~1.5" hose leading to a steel pipe that heads toward the air pump.

First remove the air intake hoses and air box. The mass flow sensor comes out with the air box. Detach its electronics connector to remove the air box.

While the air box and mass flow sensor were out, I replaced all the accessible o-rings in the induction system and replaced all the old rubber fuel lines and cloth-coverd vacuum hoses under the induction system.

Cover the air intake of the induction system with a rag so you don't drop anything into it.

It's easiest to remove the diverter valve as a subassembly with its previously-mentioned short hose and pipe. First pull the cloth-covered vacuum hose off and mark it with some masking tape.

There're two brackets mounting the emission system's pipe/short hose/diverter valve to the RH head. They're held down with two M6x 1.0 hex-head bolts. The head size of the bolts is 10mm. The forward fastener is easily accessible. The aft one is barely accessible, since it's directly under the diverter valve and access is impeded by the coolant reservoir and windshield washer reservoir neck. I needed to use a u-joint, inline with a short and long extension to remove the aft bolt. A ground wire from the injector system attaches to each of these fasteners. Be very careful about the electronic connectors to your injectors when you're messing about removing the bolts and ground wires, since the connectors are probably 19-year-old Bosche ABS and are quite fragile.

After you get the two bracket screws out, disconnect the hose that heads off to the catalytic converter. Then disconnect the hose that leads to the air pump.

The coolant reservoir is held in with the j-hose and two M6 hex head mounting screws. Again, the head dimension is of the screws is 10mm.

Since the j-hose was rotten, I found it easiest to cut it in its visible section between the reservoir and its connection to the y pipe. I dealt with the stub ends of the j-hose after the reservoir was out. Remove the two coolant reservoir mounting screws from the corners of the reservoir. Disconnect the coolant level sending unit connector. I left the radiator-to-coolant reservoir hose intact, since I'd recently replaced it. Your's likely needs replacement. Replace it. If you're replacing the coolant reservoir, unhook the radiator-to-coolant reservoir hose, too.

Now you should be able to wrestle the reservoir out. Note the angle/position of the j-hose. If replacing the coolant reservoir, mount the new hose to the new coolant reservoir and compare to the old coolant reservoir/old j-hose subassembly. Correct as necessary. If not replacing the coolant reservoir, Remove the old j-hose and install the new one, per the index marks you've made for the old j-hose.

Reverse the procedure to reinstall. I used some "slobber" to ease installation of the j-hose on the reservoir and y-pipe. I also cleaned up the steel pipes with 3M red abrasive cloth. Be sure to install the j-hose in the same angle/position as it was on the old coolant reservoir, or you're in for a bit of a wrestling match. If you're replacing the reservoir, you'll need to move the coolant level sensor from the old reservoir to the new one. I cleaned up the electrical connectors and contacts on the coolant level sending unit with electrical contact cleaner from Radio Shack. I applied Vaseline to the contacts to protect them from corrosion, down the road. Be sure to clean up the path to ground for the fuel injector ground wires, before re-assemby. I also replaced the air pump hoses, while I had all this stuff out.

928 Int'l helped me out tremendously with all the hoses for the air pump system, induction o-rings, and cooling hoses. I replaced all of the induction/air pump hoses, while this subsystem was out.

Best Regards,
Mark Zeh
'82 Weissach