Re-posting this from another thread, as I suspect it may have gotten buried there.

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So, I have more questions (about my Discovery II overheating) that all seem to tie to the reservoir tank. I've been trying to remove things from the equation to figure out why I'm still getting too much pressure in the hoses and overheating. I wanted to pressure test the radiator to remove that as a factor and rented a pressure tester at AutoZone (for free, too! Great store.). However, the pressure tester was clearly designed for a radiator with a cap, which the LR doesn't have. I finally found an attachment that would attach it to the reservoir tank. But ... when I pump pressure into the reservoir, the pressure was immediately "leaking" out through the reservoir's overflow/drainage hose.

Is there some workaround to this? If not, it seems really difficult to pressure test a cap-less radiator. Could you just stick a thumb on the end of the overflow hose, or is there too much pressure going to be built up for that to work? I didn't want to proceed and potentially get false-negative results because pressure was actually escaping without me knowing.

Next question on the reservoir ... if I keep the cap loose, does this disrupt the proper functioning of the cooling system? It relieves the problem of having too much pressure in the hoses because the pressure is obviously escaping from the loose cap, BUT ... is that because it's actually failing to keep pressure in the system at all and therefore not circulating coolant correctly (and ultimately resulting in more overheating)? When I run the vehicle with the cap loose, it feels like there's NO coolant running through the upper hoses (I can squeeze them all in the way without any flow pressure), but there IS coolant spitting out of the upper hose bleed valve when I release it.

Haven't tried the block sealer yet. Wondered if there was maybe a simpler answer relating to the reservoir before proceeding with the multiple flushes, taking out the thermostat, etc.

I checked for any untoward gunk in the oil filler cap. Also took out the plugs and looked inside the plug sockets, and saw nothing unusual. So there at least isn't those signs of blown gaskets or anything.

I've also read that any minor damage to the blades of the fan can cause overheating. Anybody experienced a resolution to overheating problems by replacing the fan?

Just trying to look at all possible causes. It's maddening trying to figure this out vs. dumping my vehicle.

Thanks,

Dan

 

The coolant reservoir is pressurized.
You need the correct adapter for the AutoZone kit to work.
You can plug the overflow tube and then pressure test.
Yes leaving the radiator cap loose will cause the engine to run hotter, the reason you pressurize a cooling system is to increase the boiling temp of the coolant.
Remember that water boils at 212*F, your engine runs around 200*F, pressurize it to 15psi and now it will take 250*F to boil it over.
DO NOT put block sealer into your system.

 

Thanks Spike.

What do you suggest blocking it WITH? Is a thumb enough? Vice-clamping it shut? Duct tape? Will that create enough blockage to not disrupt the pressure test?

I'm curious why there's so many block sealer products if they're so bad for engines? Is it just a sucker novice's choice (and the sellers know this)? I have read on other forums that people have used it as a last resort on an otherwise screwed engine (cracked cylinders) to successfully get another few months out of it.

Thanks,

Dan