Paso Thermostat/Cooling Hose Replacement mod.
Posted: Tue Apr 21, 2009 8:26 pm
Ducati Paso Thermostat & Cooling Hose Modification:
The original Paso thermostat is no longer available from Ducati. These were bypass thermostats that routed coolant from the heads to the top right angle feed. When cold, the coolant would exit the side outlet, returning to the water pump. When warm, the bottom opens, forcing the coolant thru the radiator before returning to the water pump. Ducati makes another bypass style thermostat that was used on the 996, ST2, and ST4. Its top right angle feed is opposite the Paso’s version, and also smaller in diameter. It must be mounted similar to the 996 orientation (see picture below). Since the junction hose on the Paso will no longer fit this orientation, now is a good time to replace it and all the unique hoses that are becoming difficult to find. One alternative is to use the 996 Junction block also shown in the picture. This slips over the horizontal head outlet and has connections for the vertical head, thermostat bypass, and upper radiator hose. It also has openings for the fan switch, temperature sensor, and thermistor. These can either be plugged or used in place of the Paso pipe that mounts under the tank. If replacing the original Paso pipe, Speedway Motors offers a 1” aluminum hose connector that is 6” long and has a bead on each end for $12. http://www.speedwaymotors.com/Aluminum- ... ,8936.html. I have not checked thread size compatibility between old and new sensors yet, so someone PM me with updates.
The picture shows the approximate position of the 996 components as they would mount in the Paso. The junction block would be inboard of the frame up against the head. Its forward 1” connection needs to turn a right angle within 2” of the radiator and rise 6” before turning another right angle under the tank. 1” Barbed fittings like the ones shown here can be trimmed to fit in 2”, with .75” of hose overlap before the 90 degree elbow. http://www.fittingsandadapters.com/90hosmenbras.html . Samco Superflex 25 mm hose could probably route right to the radiator filler neck if you have already performed the Paso Coolant tank modification that I published last year and you want to eliminate the pipe listed above.
The smaller head outlet diameters measure 21.2 mm, so I believe 19 mm diameter Superflex could be used http://www.sporthoses.com/parts/straight_superflex/. The upper rear facing outlet from the union will connect to the vertical head. The lower outlet can use a piece of the 996 union/head hose or Samco hose elbow to turn 90 degrees and pick up the thermostat top inlet. The water pump return can use another 1” 90 degree barbed fitting to connect to the existing Paso water pump return hose or equivalent. Finally, the radiator outlet to thermostat is a pretty straight shot, so any piece of 25 mm hose will do. Below is a list of the parts you will need to get started:
Description Ducati Part Number
996 / ST2 /ST4 Thermostat 553.4.003.1A
996 Junction block (mates to outlet below) 779.1.121.1A
996 Horizontal head water outlet 814.1.036.1A
996 Vertical cylinder water inlet hose 800.1.007.1A
A word of caution, unlike the Coolant Tank Modification and the Dual Headlight conversion, I have not actually performed this modification. Comments or updates can be sent to me (Shelboss) via PM or posted in this thread. Let's keep these old beauties rolling!
Art
The original Paso thermostat is no longer available from Ducati. These were bypass thermostats that routed coolant from the heads to the top right angle feed. When cold, the coolant would exit the side outlet, returning to the water pump. When warm, the bottom opens, forcing the coolant thru the radiator before returning to the water pump. Ducati makes another bypass style thermostat that was used on the 996, ST2, and ST4. Its top right angle feed is opposite the Paso’s version, and also smaller in diameter. It must be mounted similar to the 996 orientation (see picture below). Since the junction hose on the Paso will no longer fit this orientation, now is a good time to replace it and all the unique hoses that are becoming difficult to find. One alternative is to use the 996 Junction block also shown in the picture. This slips over the horizontal head outlet and has connections for the vertical head, thermostat bypass, and upper radiator hose. It also has openings for the fan switch, temperature sensor, and thermistor. These can either be plugged or used in place of the Paso pipe that mounts under the tank. If replacing the original Paso pipe, Speedway Motors offers a 1” aluminum hose connector that is 6” long and has a bead on each end for $12. http://www.speedwaymotors.com/Aluminum- ... ,8936.html. I have not checked thread size compatibility between old and new sensors yet, so someone PM me with updates.
The picture shows the approximate position of the 996 components as they would mount in the Paso. The junction block would be inboard of the frame up against the head. Its forward 1” connection needs to turn a right angle within 2” of the radiator and rise 6” before turning another right angle under the tank. 1” Barbed fittings like the ones shown here can be trimmed to fit in 2”, with .75” of hose overlap before the 90 degree elbow. http://www.fittingsandadapters.com/90hosmenbras.html . Samco Superflex 25 mm hose could probably route right to the radiator filler neck if you have already performed the Paso Coolant tank modification that I published last year and you want to eliminate the pipe listed above.
The smaller head outlet diameters measure 21.2 mm, so I believe 19 mm diameter Superflex could be used http://www.sporthoses.com/parts/straight_superflex/. The upper rear facing outlet from the union will connect to the vertical head. The lower outlet can use a piece of the 996 union/head hose or Samco hose elbow to turn 90 degrees and pick up the thermostat top inlet. The water pump return can use another 1” 90 degree barbed fitting to connect to the existing Paso water pump return hose or equivalent. Finally, the radiator outlet to thermostat is a pretty straight shot, so any piece of 25 mm hose will do. Below is a list of the parts you will need to get started:
Description Ducati Part Number
996 / ST2 /ST4 Thermostat 553.4.003.1A
996 Junction block (mates to outlet below) 779.1.121.1A
996 Horizontal head water outlet 814.1.036.1A
996 Vertical cylinder water inlet hose 800.1.007.1A
A word of caution, unlike the Coolant Tank Modification and the Dual Headlight conversion, I have not actually performed this modification. Comments or updates can be sent to me (Shelboss) via PM or posted in this thread. Let's keep these old beauties rolling!
Art