Rocket 3 Roadster Possibly Overheating?

atomsplitter said:
Grand plan.
Click to expand...
Interesting news, the radiator cap from Amazon came today so I got straight to work, but it was the wrong cap. However, I didn’t know that going in so when I went to fix the coolant issue, I discovered some very interesting things that I thought maybe everyone should know.

1) first thing I did was unscrew the safety screw from the radiator cap and open the radiator cap. Now the bike has been off for close to four days and I made sure to sit the bike upright. As soon as I screwed off the cap coolant start spilling everywhere, which was totally unexpected. It was so filled to the brim that the cap was entirely off and it was still spilling for seconds. I had to get my rag to soak it up.

2) the next thing I did was unscrewed the bleed bolt, but even before un screwing it, I took a closer look, and I saw some orange coloring there around the rim. As soon as I unbolted it almost halfway out, coolant started to stream out very slowly almost until like to a bulge, the more I left it open the more coolant slip slipped out. As the coolant was leaving the bike, I didn’t see any bubbles, but I didn’t have to pour any coolant from the radiator because it was already filled to the brim.

3) so what I did next was I bolted back the bleed bolt and I went to put the new cap in but the new cap is way too big! I then realized looking at our past discussions on this thread that at first the radiator cap suggested that I get besides the OEM was a 10230 Radiator Cap, but the Amazon link you sent me pointed to 10231 radiator cap. I’m guessing the numbers means something. I didn’t bother to check and ask to see which one was correct but needless to say the cap that I have is just way too big.

4) so for now I put the old cap in lost the safety screw. It fell somewhere on the bike. May rest it peace and now I’m waiting for the new pressure cap the correct one to come which is I’m guessing the standard OEM part, or do I go to my auto parts store and get the one that will best fit my bike.

So, with how the coolant reacted, what does that tell you? Could the cause have been just a bad radiator cap this whole time?
 
buddazero said:
So, with how the coolant reacted, what does that tell you? Could the cause have been just a bad radiator cap this whole time?
Click to expand...
Yup. I won't bore you with the science behind it, so take your OEM cap to the auto parts store and see if they can match that up. Sorry for the mix up I was pretty sure I had the right part number but didn't verify before posting it. Your best bet is to see what the auto parts store has as a match, it won't be chrome shiny, but should work until the chrome one shows up. Send the one you got back for a refund. Also make sure the expansion tank is filled below the MAX mark.
 
atomsplitter said:
Yup. I won't bore you with the science behind it, so take your OEM cap to the auto parts store and see if they can match that up. Sorry for the mix up I was pretty sure I had the right part number but didn't verify before posting it. Your best bet is to see what the auto parts store has as a match, it won't be chrome shiny, but should work until the chrome one shows up. Send the one you got back for a refund. Also make sure the expansion tank is filled below the MAX mark.
Click to expand...
No worries at all I spent more money buying lotto tickets in the past haha!

Also, you’re not boring me with the science, you actually explained it earlier by saying that if it’s not a pressurized system, then the coolant will boil a lot earlier than it should or something like that right? And a leaking cap is a no go.
 
buddazero said:
No worries at all I spent more money buying lotto tickets in the past haha!

Also, you’re not boring me with the science, you actually explained it earlier by saying that if it’s not a pressurized system, then the coolant will boil a lot earlier than it should or something like that right? And a leaking cap is a no go.
Click to expand...
If it's not boring I'll give you the skinny on the pressure cap. The reason the system is pressurized is to ensure a minimum subcooling of the fluid. At the suction eye of the water pump's impellor fluid pressure drops as the impellor rapidly accelerates the fluid thru the pump. This rapid acceleration (velocity) is converted to pressure in the volute (In fluid mechanics, a volute refers to the spiral-shaped casing around a pump impeller. Its purpose is to gradually expand the flow area, slowing down the fluid velocity while converting kinetic energy into pressure energy. This design is common in centrifugal pumps). That means the pump suction has a required minimum net positive suction head requirement (NPSH). If the suction pressure drops below that NPSH the fluid can cavitate inthe suction eye meaning bubble formation in the suction eye of steam and loss of pump total flow (NOT total loss of pump flow). If the pressure cap is leaking, then the fluid reaches saturation temperature at 212F (less at higher elevations above sea level) and the NPSH is lost and the fluid flashes to steam in the suction eye of the impellor. The water pump doesn't move vapor so becomes steam bound in severe cases or sloshes a mix of water and steam in your water pump's case and cooling from the system is then dependent on sloshed coolant and natural circulation. The design of the system permits a good deal of cooling via this natural circulation however temperatures will be elevated from norm. Natural circulation is possible if the heat source is below the heat sink (motor mounted lower than the radiator), which is why the cooling system return goes to the top of the radiator and radiator outlet to water pump is taken off the bottom. Hot water rises due to the change in density and cold water falls because it is denser (more mass per unit volume) and so cooling is maintained, however the driving head for this natural circulation flow is the differential temperature of the hot side to the cold side. The greater the differential temperature the faster the flow. So, while the pump is just sloshing a steam water mix cooling flow is occurring at a reduced rate from sloshed water steam and natural circulation driven by low-density steam/water at the top of the engine being pushed out by cold water entering the bottom of the engine. The air going across the radiator fins cools the steam water back to subcooled liquid that gets flashed at the suction eye and while cooling is happening your temperature gauge is reading a lot higher than normal. Sound familiar?
 
Last edited:
atomsplitter said:
If it's not boring I'll give you the skinny on the pressure cap. The reason the system is pressurized is to ensure a minimum subcooling of the fluid. At the suction eye of the water pump's impellor fluid pressure drops as the impellor rapidly accelerates the fluid thru the pump. This rapid acceleration (velocity) is converted to pressure in the volute (In fluid mechanics, a volute refers to the spiral-shaped casing around a pump impeller. Its purpose is to gradually expand the flow area, slowing down the fluid velocity while converting kinetic energy into pressure energy. This design is common in centrifugal pumps). That means the pump suction has a required minimum net positive suction head requirement. If the suction pressure drops below that the fluid can cavitate meaning bubble formation in the suction eye and loss of pump total flow (NOT total loss of pump flow). If the pressure cap is leaking, then the fluid reaches saturation temperature at 212F (less at higher elevations above sea level) and the net positive suction is lost and the fluid flashes to steam in the suction eye of the impellor. The water pump doesn't move vapor so becomes steam bound or sloshes a mix of water steam and any cooling from the system is then dependent on natural circulation. The design of the system permits a good deal of cooling via this method however temperatures will be elevated from norm. Natural circulation is possible if the heat source is below the heat sink, which is why the cooling system return goes to the top of the radiator and radiator outlet to water pump is taken off the bottom. Hot water rises due to the change in density and cold water falls because it is denser (more mass per volume) and so cooling is maintained, however the driving head for this natural circulation flow is the differential temperature of the hot side to the cold side. The greater the differential temperature the faster the flow. So, while the pump is just sloshing a steam water mix cooling flow is occurring at a reduced rate from natural circulation driven by low-density steam/water at the top of the engine being pushed out by cold water entering the bottom of the engine. The air going across the radiator fins cools the steam water back to subcooled liquid that gets flashed at the suction eye and cooling is happening but your temperature gauge is reading a lot higher than it should. Sound familiar?
Click to expand...
Sounds very familiar yes. So the gist is that the system needs pressure to work, but with a leaking cap, pressure cant build up...i think
 
Did you drain the expansion bottle or leave it hanging upside down before removing the rad cap?
 

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