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Leaking coolant reservoir cap

Snr Member
Posts: 263
Joined: Fri Oct 23, 2015 12:12 am
Location: Germany (South-West)

Leaking coolant reservoir cap

Postby XJ4081 » Fri Jul 31, 2020 11:11 pm


I repeatedly noticed a loss of coolant fluid through the reservoir cap, especially after driving mountainous roads or stop-and-go traffic. When examining the cap I noticed that the inner upper rubber sealing has almost gone. So I got me a new cap and ... the issue remains the same :shock: . In the past year I already had noticed a loss of coolant on hot days (by its sweetish smell when burned on hot surfaces), but I could never locate a leak. This year I don't have this issue, it seems all to come through the cap, maybe the weekest point in the system.

Several times I also noticed that the coolant temperature had raised beyond the N-mark in the gauge when the cap leaked. In think this could be no coincidence but be related somehow. Is it getting too hot in the system so the pressure is becoming too high and it leaks at the weakest spot? Or is there too much fluid in the system so the pressure rises too high when the coolant becomes hotter (how can I determine the proper fill level, the reservoir has no marks)? Or is the cap not tightened accurately (I simply tightened it with my bare hands, in order to untighten the old one I needed a gripper)?

Best regards
1993 XJ12

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