Spider tank relocation

If I mount my spider tank to the firewall, do I just have to make sure it is the high point in the system. Any other considerations or thoughts?

Hi Josh,

I might take a stab at this since you have not received any responses yet.

Rotax locates the spider tank on top of the engine, likely in consideration of minimizing the length of the hose runs and therefore minimizing the hydraulic friction with the coolant and reducing the amount of materials used to connect stuff.

As far as the high point of the cooling system is concerned, the spider tank only has to be above the water outlet on the cylinders - think in terms of that is where you fill the system. For the plastic overflow tank, that can be above or below the spider tank since the overflow hose is sealed between the spider tank and the overflow tank; however, the plastic overflow tank normally ends up at the top of the firewall on the port side because the level can be easily checked through the oil door (once the system is known to be free of air)

With the options on your engine, you might not be able to put the spider tank right on top of the engine where it normally sits; but, might be worth considering minimizing the amount of hose/tubing the hot water coming of the top of the engine has to go through to get to the radiator.

Oh yeah.....if you check the price:eek: of the rotax hose for connecting the spider tank to the top cylinder fittings.......that could possibly sway a person in the direction of keeping the runs as short as possible;). Rotax is very, very proud of their hose.

Hey Dave, thanks for the reply. I actually was able to raise my manifold by half an inch which gave me juuust enough clearance to get the hose under. I ran short of hose so I still have one connection to make but here’s where the tank is now.

Hi Josh,

Looks good.

If I recall correctly, part of the puzzle with the ULS was relocating the spider tank a very short distance towards the back of the engine for routing the aluminum down-pipe towards the radiator. I think there was a need to rotate one of the top cylinder elbows also. Your mileage might vary on the 914.

Hi Josh,
I didn’t use the rotax spider tank at all on my build.
I took the 4 hoses from the heads and routed them into a 4 in 1 out manifold
Located at the rear of the engine.
I use a pressurised expansion tank mounted high on the firewall.The expansion tank has 2, 3/8 hoses, one from the 4/1 manifold,one from the thermostat
housing,and a 1/2” hose going to the inlet side of the water pump.
The 3/8 hose from the 4/1 manifold is routed thru my heater core,before it
Goes to the expansion tank.
The 3/8 hose from the thermostat housing is routed thru carb body heaters
before it goes to th expansion tank. Works great so far!

You can see the expansion tank,and the return hose if you look carefully.

Thanks for showing me what you did on yours I had though of a header as well. Here are pictures of what I ended up doing.

Looks good, might want to route the plug wires over the hoses.:):)

Ah will do. I just assumed since the wires were laying on the engine originally and the wires didn’t have a ton of slack it would be ok.