The Rotax 912 ULS engine has an oil pressure sending unit located on the forward bottom right corner of the engine. Quite a few builders have experienced the oil pressure sending unit going bad prematurely from what many believe may be engine induced vibrations. Once again DOG Aviation is attempting to make a preemptive strike in the hopes of having trouble free operation from the oil pressure sending unit … this will be accomplished by relocating it to the firewall and using a rubber mounting grommet. The new home for the oil pressure sending unit will be adjacent to the fuel pressure sending unit on the modified dual mounting bracket fabricated a couple of months ago.
To accomplish moving the oil pressure sending unit, Aircraft Specialty
came to the rescue. Aircraft Specialty has a kit developed for the RV-12 to
move the oil pressure sending unit to the firewall. The kit includes an adapter
fitting for the block of the Rotax engine, a restrictor fitting, Teflon hose and
an adapter fitting for the oil pressure sending unit. Because I was striving
for an aesthetically pleasing mounting for the oil pressure sending unit, decided
on making a modified dual sending unit bracket so both the fuel and oil
pressure sending units can be mounted together on the firewall. Because this
mounting is at a different location, Steve at Aircraft Specialty sent me all
the fittings and suggested I remove the sending unit from the engine, install
the fittings and run vinyl tubing between the fittings to determine the exact length
of hose necessary … then return the fittings back to Steve so a custom oil pressure
hose can be fabricated.
Removing the oil pressure sending unit from the engine … a paper towel ready
to catch oil but not a drop came out of the oil pressure port when the sending
unit was removed.
The Aircraft Specialty supplied fittings that will be installed on the Rotax engine at the oil
pressure port … the left fitting screws into the port on the engine where the oil
pressure sending unit was removed, the 45 degree fitting on the right has a restrictor
built in and screws onto the fitting to the left.
Following Steve’s suggestion, the fittings were installed on the engine
and a piece of vinyl tubing was attached and routed to the new home for the oil
pressure sending unit on the firewall and a measurement was made for the
amount of hose necessary. Also of note, the Rotax Illustrated Parts Manual
shows Loctite 243 used on the oil pressure sending unit’s threads, so the threads
on the fitting installed in its place had Loctite 243 applied to them. Initial
thoughts were to run the Teflon hose under the engine but after thinking it through,
decided the safest route was to run the hose up and across the top of the
engine where it can stay cooler and away from the heat of the muffler and
My finger is pointing to the adapter fitting and restrictor fitting installed in the oil pressure
port on the engine ... the 45 degree flair fitting with vinyl tubing attached
so a measurement could be made on the length of hose necessary to relocate the
oil pressure sending unit to the firewall.
At the firewall, an adapter fitting will sit in the rubber grommet and serve
as an interface between the oil pressure sending unit and the Teflon hose fitting. The
fitting used for measurements in the photo below is a 45 degree fitting …
however, the Teflon hose will be made with a 90 degree fitting for the firewall
Measuring the amount of tubing necessary to reach the new mounting location for the oil pressure sending unit on the firewall. The Teflon oil pressure hose which will
connect to the oil pressure sending unit at this end will have a 90 degree fitting and not
the 45 degree fitting shown in this photo.
Decided for my application the actual length of the hose material not
including the fittings needs to be 37".
Return from the future:
The changeover to Aircraft Specialty’s remote oil pressure sender kit
has finally been completed (well almost). Covered on a posting February 5,
2016, felt it would also be best if I were to return from the future and edit this
post as a follow-up on installing the remote oil sender hose from Aircraft
Specialty ... especially since this entire post covers their remote oil sender kit for the
RV-12. As mentioned earlier, measurements were taken using a vinyl hose so
Aircraft Specialty could make a custom remote oil sender hose for the DOG
Aviation RV-12 utilizing a different fitting and length than the one they would
normally supply in their retrofit kit. The reason for this, as mentioned earlier,
is because a special mounting bracket was fabricated so both the oil and fuel
pressure sending units could be mounted together in a bracket on the RV-12’s
firewall. After measurements were taken and passed on to Steve at Aircraft
Specialty … three days later, DOG Aviation’s receiving department took delivery
of a custom, quality built, conductive Teflon hose in fire sleeve. Have to say,
the customer service from Steve and follow-up has been nothing less than
outstanding for each of the five kits that have been purchased from Aircraft
Specialty for the DOG Aviation RV-12 … Teflon brake line kit, Teflon fuel line
kit, Teflon remote oil pressure sender kit and the totally slick canopy locking
The custom Teflon hose made for the DOG Aviation RV-12 by Aircraft
Specialty is a different length and has a 90 degree fitting where a straight
fitting would normally be on their standard kit hose.
There are two mounting options possible with the hose I ordered …
depending on the final location for the voltage regulator. If the German built
Silent Hektik (or Ducati) voltage regulator is mounted using the old mounting location
on the firewall shelf reserved for the voltage regulator, the remote oil sender
hose can be routed across the top of the Rotax engine, down under the engine
mount and then sweep over to the oil pressure sending unit on the firewall.
This arrangement still allows for a cooling cap to be installed over the
regulator and room for the cool air blast tubing to supply cool air to the regulator.
The hose for the remote oil pressure sending unit is routed so it won't interfere
with the cooling shroud or blast tube if a voltage regulator is mounted on the
firewall shelf. Because the regulator sits directly under the oil pressure
sending unit, with the hose paralleling the firewall, there is plenty of
room for the shroud and blast cooling tube used to cool the regulator.
The other option available which is likely better (especially for those
who have followed Van’s latest mounting instructions to move the voltage
regulator under the instrument panel shelf) is to run the hose for the remote
oil pressure sender following the same path as the hose for the fuel pressure
sending unit. The hose length I chose will work for this route, but ideally
could be an inch or two longer.
Hose for the remote oil pressure sending unit routed along the same path
as the hose to the fuel pressure sending unit. This may be a
preferred solution if the voltage regulator is not directly under the oil
pressure sending unit.
At this point in time, the final decision has not yet been made on where
the voltage regulator will be mounted, so only the engine end of the remote
hose will be tightened ... the fitting on the sending unit will remain loose
until a final decision is made regarding the location of the voltage regulator …
which will dictate which way the firewall end of the remote oil pressure sender
hose needs to be routed.
The Aircraft Specialty conductive Teflon hose for the remote oil
pressure sending unit is connected at the lower right portion of the Rotax 912
ULS engine via the supplied adapter/restrictor fittings installed on the engine's