Vacuum coolant fill kit recommendations

[Rubio]

The fill kits that I’ve seen available don’t have adapters small enough for the 30 mm neck in the thermostat housing. Some have a conical adapter but I wonder how well that seals and if I will need an assistant to hold it in place. Does anyone have a recommendation on a fill kit or experience using the conical adapter?

 

[Erdoc48]

In truth, when I did my coolant refill last year, I just used a long, thin funnel, filled it up to the neck with that, fired up the bike, let it warm and then kept filling until I couldn’t see anymore spouting of the coolant. It was up to the filler neck at that time and then I put the cap back on. No special adapters were needed.

 

[SMSW]

I've never used any special tools to fill my bikes (or cars) w/ coolant. If possible, I poured the stuff right from the jug into the radiator, on my bikes I've used a funnel. Back in my Guzzi days, a friend told me to buy a long neck funnel, then he pulled out a heat gun and bent the spout to make filling the carankcase w/ oil easier. That single funnel has seen more use than any of the other half dozen funnels (big, small, offset, etc.) that I have in my collection. @Erdoc48's method works fine - fill, burp the bike, add more, etc.

I've never heard of filling the cooling system through the thermostat housing, nor have I heard of using a vacuum device. IIRC, most of my cars had a purge valve on the heater core that was the high point of the system. That hole in the thermostat (that we are supposed to put at 12 o'clock) serves the same purpose - letting air bubbles out of the block to be collected in the radiator.

 

[Rubio]

I did similar last year and it burped after several rides before it was full. I would let it cool, take the rad cap off and top it up. You have to take so many body pieces off to put the fairing packet back on after it’s full so I thought a vacuum fill would be a one and done.

 

[tonythecarguy]

The smallest "square" rubber adapter from UView 550000 air lift kit has worked on the radiator neck of my ST1300 many times.

Using an vacuum fill device is more work than finding a funnel and pouring the coolant in; Get the air compressor filled up, don't knock over the jug of coolant you are sucking from, don't trip over the compressed air supply hose and knock the addapter out of the radiator, don't let the suction hose lift out of the jug while filling, then rinse out all the hoses and parts and but it back into its slightly too small box. However when I do work in the winter and filing the coolant is in the middle of many tasks and the engine will not be ready to start for a few weeks it is nice to have the coolant part of the work completed and I dont have to remember to go back to the burping step weeks later. Addionaly pulling a vacuum and seeing how long it will hold is a decent check for major leaks before you put the bike back together.

 

[Erdoc48]

If you want to talk about a difficult drain and fill, I recently changed the coolant in MR2 Spyder. In that car, the engine is in the back and the radiator is upfront with the lines running under the car. It’s kind of a complex operation and you have to run extra clear hoses from a bleeder on the radiator as well as a bleeder on the heater core. Keep filling from the back since the radiator doesn’t have a fill point, the system gradually fills over time and keep adding fluid until you see the coolant in the lines that you hooked to the heater core and the radiator. I wanted the garage to do it, but they were going to charge an exorbitant rate just to change coolant I guess because they realize it’s kind of a pain to do. I did get it done and if I had to do it again, I probably would’ve used my vacuum pump to pull the air out of the heater core bleeder. It would’ve been off faster that way, but I didn’t think about it at the time. I kept compressing the rubber hoses in view in the “frunk” area of the car and little by little I got it to the point that there was no air in the lines. The key is firing up the car and realizing that you have heat and that’s an indicator of success. I used a Prestone 15 years/350 K mile coolant which is a 56/44 mix of coolant to water and of course used distilled water. This is the same coolant I used in the bikes as well. I did that in 2025 so I won’t be doing it for some time. I would say the absolute easiest coolant drain and fill is on the Silverwing because with that all you have to do is take out the little storage box on the right and it is just a little light squeeze of plastic (takes seconds) and just remove it and the thermostat neck is right there. The drain point is the lowest point on the bike. So it is insanely easy to do. I even use the little piece of hose to blow whatever extra coolant out of the block that I could and basically really got nothing out since it’s drained via the lowest point on the bike. however, despite the little bit of disassembly with the ST, I didn’t find it that difficult.

 

[Erdoc48]

I did similar last year and it burped after several rides before it was full. I would let it cool, take the rad cap off and top it up. You have to take so many body pieces off to put the fairing packet back on after it’s full so I thought a vacuum fill would be a one and done.

Actually, if you didn’t feel when you did it that the radiator was full, it’s supposed to pull coolant that is in the overflow so all you really needed to do was filled up as much as you could via the regular filler neck, then use the overflow bottle for extra if it was necessary. In other words, monitor the overflow and then just fill that up a little bit to the top line and then all would’ve been fine and your system would’ve been filled at that point.