So, I'm in the process of getting my coolant leak found, repaired, ect. Have a few questions... Can I use the pressure tester from the overflow cap or do I have to use it from the drain plug? Also, how hard is it to remove the underpan? I'm assuming a dozen bolts? I couldn't find much on the forum. Any tips? I plan to use a Lisle spill free funnel to fill also. Should be a breeze hopefully. Thanks!

 

SandCat, when pressure testing the coolant system, you do it from the overflow bottle (atleast that is how I have done it every time I have needed to do it.

As for the plate under the car, it is in a few pieces. Basically you have one that does the curve of the bumper, one that does the next like 18 inches, then the 3rd goes all the way back to the tail of the tranny. You should really only need to remove the 3rd plate to do what you are after. This has 2 (possibly 4) bolts that go into the tranny, then you have 2 that are holding it to the frame of the car at the very back, then you have like 12 fasteners near the front holding a majority of the plate and they make a big circle from 1 tire to the other with like 3 in hte middle. Not hard to remove. I want to say it is a whole bunch of 10mm bolts (possibly a few T25(?) bolts). Not hard to get unbolted, but is a little clumbsy in trying to slide it out from under the car. I normally just push it back towards the rear tires.

 

You shouldn't need to remove the two underside panels to find almost any coolant leak. They can be found from the topside.
There is one panel that runs the full width from the front bumper to the second under-panel, about mid-engine. You would need to remove this to access the radiator if you drain the coolant.
It has a number of Torx fasteners that secure the front of the panel to the bumper, and a couple of 10mm bolts that secure it to the rear & a couple of body panel fasters (IIRC) to secure it to the fender well liners. (highlighted below).
There are two flat straight plastic pieces that are attached to the bottom of that panel for aerodynamics - secured by their own screws. Those screws do NOT need to be removed unless you're replacing those plastic pieces. They only hold those pieces to the panel & go no deeper.
The fender well liners don't need to come out unless you are looking at the associated side of the engine.


The rearward panel (#13 in this illustration) is the largest which when you peek under your Jag also runs the full width from about mid-engine rearward.
The highlighted points are where you should find 10mm fasteners that secure it. The front two fasteners also secure the rear of the front panel.
If you buy a set of auto ramps from Harbor Freight or somewhere like that, you can easily access all these with the front end driven up onto ramps.

 

Great advice posted above!

If you run into problems with the radiator drain plug take a look here;
Radiator Drain Plug

These are so cheap I would just go ahead and pick one up and any auto parts store?
Do read hafren's comments about getting the drain plug out too.
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I neglected to include a little bit of detail on those fasteners that hold the front undertray to the bumper.
There are actually 16 Torx fasteners along the front. 10 of them are easy to see, but 6 of them are deeply recessed into cups, so you have to look for them in the recessed cups, not in plain view if you don't know to look for them.
Then there are the five fasteners towards the rear of the front panel, 3 that secure the rear of the front panel to the front of the rear panel, and the 2 angled fasteners that secure the rear of the front panel & front of rear panel to the frame.
Then there are 2 screws at the bottom of each wheel well liner that secure the panel to the liner.

 

Awesome replies, thank you so much! I can't wait to get this done. Any advice for draining and flushing? I've heard it's near impossible to get it all out. What's in there now is blue mystery coolant, and I'll be putting in proper spec orange dexcool, I'd hate for some horrible chemical reaction from mixing 2 kinds. Current plan is to fill and drain repeatedly with distilled water until it's as clear as I can get it, then refill.

 

Yes that's all I do is keep changing it with water until it runs clear. Yes your right it's pretty much impossible to get a complete drain and you will see this when you refill. I have run Thermo-Cure for a week or so too but not sure you need it?
Thermo-Cure

Made by the same people that make Evaporust if you have ever used that.

I post this a lot but I recently got a vacuum refiller tool and now it's one and done on any car for me! I wish I had got this years ago as it just plain works!
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Sandcat, I would recommend investing in a number of gallons of distilled water. In this case, having an aluminum radiator, this can affect the longevity of the radiator. Tap water has certain minerals in it that can help promote corrosion of the coolant system. Distilled water does not have these. It may seem trivial, but I make my living from knowing the difference between different types of water and how they affect a system. Salt water will make a nuclear fail potentially in minutes. Sounds somewhat impossible, but, having seen the effects of even low level water contamination, it can get impressive under high heat/pressure.