Hi

Just changed a coolant tank on my super v8.
Did notice that the new replacement cap came with 140kpa rating instead of the original 120kpa.
The oem part number is replaced by a new number for the x358 so I guess they upped the rating for the cap on the facelift version.
Does anyone know why, whats the benefit in doing this? With higher pressure the coolant can withstand higher temprature without boiling, but it would also put more stress in the system/hoses.
I have not had any overhating problems with the 120kpa cap.

Really tempting to just use the original 120kpa cap

 

Odd, I had the opposite problem. The original was 140kpa, with the new replacement I bought being 120kpa. I ended up just using the original 140kpa.

 

Thats strange, we both have 2005 models. Maybe its a difference between USA and ROW ?

 

I’ve just stumbled across this issue also although in my case the vehicle is a naturally aspirated 2012 XK X150. The factory installed cap is marked 200 kPa and the Workshop Manual says it should be 140. My cooling pipes are all original, so they’re 12 years old. The PA-12 material they are made of becomes brittle over time when exposed to heat and pressure. At 30 psi and 200 degrees F their life expectancy is about 8 to 10 years. Leaving the cap pressure at 140 kPa and changing the coolant mixture to 60/40 will buy you some time, but the only long term solution is to change all the pipes which are PA-12 to silicone or reinforced rubber. You should also replace your pressure cap about every five years. I tested my 200 kPa cap and it wouldn’t release at 200. Unless you are pushing a supercharged engine hard or live somewhere really hot, a 140 kPa cap and a 60/40 coolant mix should be adequate.