V4RG build

Went for a long ride yesterday. Temps between 75 and 85F. Bike got hot enough to boil over. The reservoir catch can was removed so it spilled out of my vent. Not sure how much coolant I lost but I think I had enough to finish the rest of the ride. I was surprised that the coolant was boiling at around 235F. I feel like this could be due to the VP Stay Frosty lower boiling point. I am considering getting a different radiator cap but not sure if anyone else has tried this and if I should be cautious about any aspect of the modification. I have the samco thermostat delete hose kit but am more concerned about the coolant temp sensor o-ring failing. Should I pressure test the system to see if the higher pressure would cause a leak? Should I just stop riding my track bike around town during the summer? We'll see if there is anything to learn from this. For now I'll top off the coolant and retest when it cools down a bit more. Here is a random picture I found that shows the reservoir/vent setup.
20250327_142435.jpg
 

BMW Alpina

FOUNDING Member & Administrator
Staff member
Something must be wrong, maybe the flow of coolant was partially blocked, or the coolant mixture is incorrect, or the flow of air to the radiator was blocked somehow... Also changing radiator cap to larger pressure should not have any bad effect.
Maybe start with changing the coolant with normal regular Ducati recommended coolant (or any automotive coolant), with the correct coolant vs water mixture.
 

HKMP7

First 9 & Moderator
Staff member
I concur because riding in AZ in 115 degs my bike doesn’t mind it at all.
 
I concur because riding in AZ in 115 degs my bike doesn’t mind it at all.
From what I can tell the bike is not running any hotter than before.
It has been up to the 4th bar heat range when in traffic. The only change is VP Stay Frosty coolant which has a much lower boiling point but should otherwise help the bike run cooler.
250F vs 400F is my guess depends on the system pressure.
I have deleted the fans so that probably doesn't help when I have to pass through a 15 mph school zone, 20 mph small town, or the occasional red light.
Bike runs normal temps on track and on the open road.
 
Black Friday shopping spree has added a few parts to the winter part upgrades que.

I2M sensor wiring and front rear suspension potentiometers
DNA air filter
SBS Dual Sinter 2 front brake pads
RCS Corsa Corta 16 clutch master cylinder

Hopefully I do not regret this as it is not a direct match to the RR brake master I also have in que but the other options are around $300-$500 more for billet Brembo options and I lose whatever functionality related to the clutch sensor. I might wire the clutch lever sensor to one of the dead buttons on my 7 button I2M left switch pod to offset this allowing starting the bike in gear etc. I don't expect any obvious improvements with this, just cosmetic and hopefully lose a few grams.
I struggle to see what benefit there is in any of these higher spec clutch master cylinders from the $332 RCS up to the $2000 billet options. If anyone wants to enlighten me, please do.

The oem v4 master cylinders will likely replace the coffin style ones on my 999 if I can get a good deal on some 30mm piston calipers.
 
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