Ok I got a new one... when driving at speeds over 45, I get the waterfall noise from the heater core area. but only over 45. I am not leaking any coolant I have bleed and re bleed the system and their is no air. any ideas, thoughts! I have looked all over and under and cannot see anything that leads to me think a leak. I have replaced all hoses with exception to heater core hose and throttle body heater. I have ordered them both and will replace as a matter of just doing. My running temp is in good shape. on the highway I am at 195-200. on the city I am at 198-204.it may shoot up to 207 after I have been on the highway and come to a stop but it will drop back down on its own or sometimes with assistance of aux. fan.

 

If you have the noise, you have air in the system and may need to get a little more creative when bleeding the system.
What do you do when bleeding the system?

 

What I did last time... I jacked up the front of the truck about 6 inches and let it sit for about a half an hour to let any air(in theory) work its way to the highest point, i.e. the bleed screw. Then I release the bleed screw, then I open the cap on the reserve tank. I started to pour coolant into the reserve. It took all of about an ounce of fluid for their to be coolant seeping from the bleed screw. I then screwed the bleed screw tight again and then the cap on the reserve tank. I have not done the hang the reserve tank yet. I did replace the water pump about a mont ago as part of my general replace program.
I should state that when I first opened the bleed screw there was a very small poof of air.

 

IMHO - if you are unable to bleed it and it keeps returning - might be exhaust gas in coolant when HG is letting go at high pressure when engine is revved up. I know this is an un-desired opinion.

One way to eliminate that possibility would be the $50 combustion gas in coolant test, which does multiple tests. One source is http://www.amazon.com/UVIEW-560000-C.../dp/B000NPDL76, there are others.

Of course, there is always the "Island Shade Tree" method to eliminate the bubble sounds ... (originally posted by Slanginsanjuan) - lol

 

When you say front of truck do you mean both front tires come off the ground? I use to do "your way" but I never could get all the air out. What I do now is jack up the side with the battery 4-6 inches off the ground. Put the heat on FULL BLAST and as hot as it goes, open up bleeder screw, start truck. Do this when your truck has sat for at least 6 hrs to make sure its completely cold. Wait until coolant starts to come out of the screw hole, then put the screw back in the hole. Turn truck and heat off. Drive it and see if it returns. NOTE: I have a Discovery one so this may NOT work for you.

 

On a later D1 or a D2 "heat on" won't change coolant flow, there is no heater valve like in earlier D1s and coolant circulates through the heater core whenever engine is running. Heres a cooling circulation plan for a D2. Might want to verify belt route, just in case.... strange things happen late in the evening under dim light, fatigue, and Red Bull and beer....

 

You need to raise the reserve tank higher than the bleed screw. Unsecure the tank and raise it up high and keep adding coolant until it comes out of the bleed screw. Tighten the bleed screw while the tank still unsecured.

 

This first^^^^

 

X3 on Homroot's advise. Remove the coolant reservoir from its usual location (hoses still attached), move it up and forward and rest it on top of the hydraulic jack location (with battery cover removed).

Until you get the reservoir higher than the bleed screw, you stand a good chance of having air trapped in the system.

 

Ok...Update. first off Thanks to all of you for your comments and suggestions. Finally got to my garage. Did a pressure test. 5lbs for 20 min all good, 10lbs for 20 min all good, 18lbs found a small seep from the hard plastic return line from the top of the radiator. replaced the hose clamp. Re ran pressure test at 18 lbs. lost approx. .5 lbs after 25 min.. The loss I think could be a reasonable loss without indication of a larger problem. Did the combustion gas test as well with a non positive outcome, talk about a breath of relief. I will do a re-bleed in the morning when engine is completely cold with the expansion tank on top of the battery cover. The funny thing is on the way to the garage I had no waterfall noise but had the noise on the way home but then it stopped.. So I will poise another question. Is it possible, should the system not being bleed properly allow the air pocket to actually travel thru the system causing the randomness of the waterfall noise over 45 mph?