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. . 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

I run my 906 with two radiators and full electronic control for the cooling fan. The standard cooking thermostat runs the engine too hot in my mind, especially if its putting out more horse power.

My 907 had been in storage for a long time when I bought it. During recommissioning I tested the thermostat and found it not to be working.

My solution was to fit a thermostat from an aprillia 1000 which only requires the use of a 90 degree silicone bend and piece of pipe.

Much cheaper than buying ducati parts.

Can you post a picture of the thermostat installed? Is the bypass maintained and the open temperature the same? Sounds like an interesting alternative to the discontinued Ducati part, thanks!

I will get a picture over the weekend and post it.

Temperature wise, it still runs at about normal around town (about 88 centigrade but stable at that temperature) with the fan cutting in as normal. However, out of town it runs at a stable 80 centigrade according to the temp gauge.

The outlet from the aprillia thermostat is slightly narrower than the original ducati item, but it does not seem to affect the operation of the system.

Pictures of the Aprillia 1000 thermostat as fitted to my 907ie









You can see that there is a slight kink in the outlet to the radiator, but I guess when the system pressurises when hot it is OK bacause the system runs a steady 80 centigrade out in the countryside at speed, and a steady 88 in town traffic with the fan cutting in and out as normal

I have not had to cut any of the original hoses. I have cut down the 90 degree red silicone bend (19mm/ 3/4" bore), and I have used a 22mm copper tube (about 75mm long) to link the silicone bend to the original coolant tube. I really need to replace this with something better, but it works for the moment without leaks.

Hope this helps someone

Sean

Thanks Sean!

I have added a few other bits on Tech FAQ for clutch, fuel pump and fuel filters.

All stuff I use on my bike with no problems.

Great bikes,

Lets keep them on the road........Cheaply!

Sean

Thanks for the pictures, this looks like a great replacement for the 907IE thermostat as long as the upper junction hose continues to be available. I would try substituting a 1" 90 degree brass elbow for the Samco elbow and copper union as this will pull the thermostat inward, make one less connection, and tighten up the fit.

The reason I used the flexible hose bend is because the outlet from the thermostat is 15mm, and the inlet to the top junction hose is about 25mm. The bend is 19mm. Squeezing the jubilee clips got a seal on either end with a 22mm copper pipe.

Not sure about connecting metal directly to plastic. Would either have to thread if the bend had sufficient wall thickness (not sure that the thermostat outlet would have), or use an industrial glue.

Either solution may not withstand the environment of thermal cycling, pressure changes and vibration in the longer term.

A solution is to use the Samco bend as I have done to connect to the thermostat, but then to replace the junction hose with silicone as well. I did buy a T piece for this purpose, but need to get the rest of the hosing. This would then pull in the thermostat so that it looks more natural.

Will post some pictures when I get it done, and let you know which hoses etc I used

Sean

Have any fair-weather riders considered running without a thermostat? Might be worth consideration, and is even cheaper...

Did this originally.

Took apart the original thermostat housing by cutting steel ring and prizing it off. Then split the unit and remove failed thermostat inside. Put things back together and sealed the unit by tightening large jubilee clip around the steel ring. Worked without leaks, but had no confidence because of potential for the jubilee clip to loosen and fall.

Another problem was that even in summer the system was only running at about 60 degrees centigrade, and it would take about 20 miles to get there. Around town would still heat to about 88 centigrade so no change there.

In winter I could imagine it would not get past about 40 centigrade.

Likely that there may be engine wear as clearances would not be taken up etc. because the engine would be working outside its designed steady state.

I read somewhere that 80 centigrade is the ideal temp for a petrol engine which is where the aprillia thermostat keeps it on a run.

Hope that answers your question

I wasn't suggesting connecting the brass fitting to the plastic housing, there would be a short piece of hose there. With the 15 MM to 22 MM transition, I like the silicon elbow too!
My thermostat was leaking and has been repaired by cutting thru the metal ring, then sealing the seam and putting a hose clamp over the now split ring. The cut from a dremel cut-off wheel and the angle on the ring work to provide good clamping force on the housing pieces.