Hey all!

After spending SO much time buttoning up the coolant system with new parts last year, I finally got it to a point where it wasn't making any trickle noises in the heater core (the last remaining part of the original cooling system). I started hearing it again, more and more, a few months ago, and noticed that the weep hole of the 4-month-old water pump was leaking. I replaced the water pump, but to my disappointment, the trickle sounds were still heard through the heater core, and have been for the last two months since replacing the water pump.

I've pressure tested the system so many times, and every time, it holds 13 lbs all day long. No leaks are visible at any hose connection. The most common place I've found leaks is the throttle body heater plate, but none there this time. No leaks around the new water pump. And since they're so cheap, I replaced the coolant reservoir cap with one from the LR dealer ($20, btw, and the build quality is 1000x better than the crap from aftermarket vendors) just in case. Tested the head gasket for exhaust gases and it's all good.

Could this simply be a stuck air bubble in the old heater core? The original radiator was JAMMED up with old Dexcool, so I'm only assuming it's the same situation with the heater core. Is there anything about changing the water pump that could've caused this? I've replaced four water pumps between the two discos, and would consider it pretty routine and straight-forward. I've never had an issue post-operation before.

Out of ideas.

 

Yes, obviously the waterfall sound is from air in the heater core. BTW, pressure test should be done at 21 psi. Factory water pump does not have enough output to push coolant through the heater core at idle. You can try buzzing the engine when cold with the cap off. Do you have the inline thermostat mod? It bleeds much better. If the air came out of nowhere you might have a blonw hg or worse.

 

Mmmm, I respect your opinion of course, but would argue that 12-13 is the correct pressure to run the test at.

And no, stock thermostat setup. Though the in-line may be better at somethings, most even, I prefer to keep it all stock. Albeit, with the lower temp thermostat.

 

Had a long discussion with a different friend yesterday on a similar subject regarding inline vs. stock. When I say it is the single best thing you can do to your Disco, I am not kidding. Anyone running the stock thermostat is asking for trouble. The question is not if it will fail, but when. I will provide more details in the inline thread so it is more widely seen, but even if you used it just to test with and went back to factory it would make things easier.

The 140 on the factory cap is 140Kpa, which is just over 20 psi. BWM actually ran some of their cars with 200kpa caps, I do NOT recommend those. I actually do not recommend the cap fully tight so the system builds pressure. A pressurized system offers limited benefits and stresses every component on the system. For a stress test though, I recommend the higher pressures.

 

Actually, that brings up something that I don't think I've ever thought about before... how tight is too tight for the caps? Just snug is good enough you think?

 

Just snug is tight enough to seal.

 

If it seals, it seals and builds pressure. This increases the boiling temperature (50/50 coolant) from about 226 deg. F to about 275 deg. F (20 psi). Pls note, the boiling point goes down at higher altitudes due to lower ambient pressure.

 

Closing out the thread - was a leaking head gasket. The water jacket at the rear of the right-hand gasket was the cause. New head gasket, no leaks!