I will be back in the S of Sweden in 2-3 weeks. Will try a fixed cap on the rad. I think another of my XKs has an identical setup but will check.
I have tried to drive with the hesder tank’s lid silighty open, but that changed nothing.
[quote=“pedermansson, post:1, topic:419922, full:true”]
Most of my Jaguars seem to run at around 70 deg. On a 140 it is 80 when driving and 84 at idle even at cool ambient temperature.
The “ideal temperature” for minimal wear is 80C, but emission reductions required the engine to run at higher temp.
The first emission standards required a hotter running temp of 84C to achieve the required reduction in emissions,
Further tightening of standards required a higher running temp of 88C.
Both of these temp required a corresponding increase in system pressure to raise the boiling point to maintain a safety margin before the system boiled.
Early Jag systems that had a 7lb. cap or lower, cannot be upgrade due to water pump seal
limitations.
XK120 140 4 lb radiator cap. 7 at some risk to the thermostat. No higher.
Nick