I did a full timing chain job on my XJ8 about 5 months ago and threw in a new waterpump and thermostat while I was in there. Since then I've replaced the crossover, expansion tank tubing, new hoses, and upgraded the thermostat housing. My lower fan crapped out about a month ago, at the same time I realized I had a slow leak somewhere in the coolant system. After some searching and a system pressure test, I pinpointed the source of the leak. Octupus hose in one of the lower legs laying across the transmission bell. At 14psi there was no leak, but at 15psi I'd get a steady drip. I confirmed the leak with the car running and some newspaper under the steering column at the firewall. I got my replacement fan this weekend and quickly had it installed. Just to check things out, I let the car run at idle with the AC on for about 30 minutes in the driveway, but the leak never showed. The octupus hose is on backorder everywhere I've checked, but I'm wondering if I still need to get one. Does anyone know if there's a pressure relief in the valve in that lower hose (area of the leak)? I've checked a few times after my wife's driven the car to work and back and there's no sign of new fluid on the bell housing and no sign of fluid drop in the expansion tank.

 

I'd guess that, with a working fan, the coolant temperature is reduced, and therefore the pressure in the cooling system is being held below 15psi. If there was a leak in the hose, it didn't disappear - replace it.