Hmm, the title says coolant cap failure, I mentioned I'm on my third coolant cap in six months, hey Mark I wonder if it's the coolant cap failing???

 

what you don't seem to understand is your cooling cap has not failed three times. For some reason like it or not your cooling system is being pressurized, other wise your cap could not have gone off at 18 psi three times.

 

The question was, what was the failure mode. What happened when they failed.

 

That's part of the problem i guess is nothing else showed up other than i could smell anti freeze, popped hood and visually noticed coolant coming from cap. That's why i'm looking for pointers on what could have caused it so i can start trying to solve the issue. I have heat so i don't think it is an airlock but maybe? Something else with motor? Possible water pump? Was just hoping maybe someone else had this issue in the past and could give me a quick answer or direction to look. Not a mechanic, don't claim to be, just trying to learn more about the disco so i can work on simple things myself. Someone had mentioned the temp gauges are inaccurate, mine seems to go right to the middle after warm up and stays there, maybe it is getting hot and blowing the relief valve on cap? Not trying to **** anyone off just suffering landrover frustration!

 

your temperature gauge will stay right in the middle even as the molten aluminum is pouring out from under your truck.
you need to have your cooling system pressure tested, it is the only way to find out for sure. everything else is a guess

 

Fern... look into getting an UltraGauge. You can mount it inside your truck as you see fit. It plugs into the OBD2 port under the dash and gives you real time measurements. Set engine temp as one of the main read outs. That will help you keep an eye on your temps. The gauge in the dash is extremely inaccurate.

Now, as far as your cap blowing off... I'm not sure why, other than too much pressure building up in your system. Like DR said, take it somewhere and get it pressure tested. That will get you started on what the issue is. It could be something simple, maybe something bigger.

Where are you getting the pressure caps from? If you are buying the wrong part, maybe that's the issue? There are a handful of suppliers that you can get parts from. Your local autozone/oreilly's/advanceauto places don't carry many parts for Land Rovers. And, if they do, the parts are usually remanufactured or cheap china crap.

 

I will add that the bottle/cap on my D2 has a "tight" point that is only about 2/3 of the way to the actual end.

If I only tighten to there, it will eventually boil over when city driving...learned the hard way.

 

Just as an aside, I still use my original coolant reservoir cap that's 121K miles and 11 years old and it still works fine. Once every year I check it , blow it through with an airline and spray silicon into it and wipe off the excess. Works great.

 

Got ya beat... my cap has 191k miles on it.

 

Update to this issue, i replace the cap reservoir cap with a higher rated one and the issue was resolved.