Originally Posted by
PhilipA
I learned something in Saudi Arabia.
I had a Nissan Sunny runabout and was at the Riyadh dealer one day to buy a new exhaust as my then 12 year old son had snapped the old one while I was teaching him to drive with a particularly vicious clutch drop.
As I was standing at the counter I noticed the Sunny parked outside start to drop coolant, so ordered a new cap as well. I fitted the new cap and no more heat soak boiling. This was in 40-45C ambient.
IMHO the role of a pressure cap is to mainly to stop boiling from heat soak once the engine is stopped.
Nearly all engines should not exceed 100C when running and for example RRC electric fans cut in at 102C and out at 97C in addition to the viscous which cuts in at about 92-94C. In my RRC they only cut in once in 13 years of ownership.
The TD5 viscous fan in my D2 cuts in loudly at about 92-94 C , so the engine is designed to generally run below that temp.
So I personally would not be comfortable if my car exceeded 100C except in very unusual circumstances.
Maybe not so crucial in a TD5, but run a V8 over 100c for long and you are asking for a moving sleeve.
BTW I note that the TD5 does not heat soak anywhere near as much as a V8. In my V8 I noticed that on hot days when I was stuck in roadworks in Queensland the temp would rise 5-8C in 5 minutes before dropping back, but the TD5 doesn't seem to rise very much at all.
Regard sPhilip A