Pulled t-stat and ran open with one of those fancy radiator burp funnels. ran it for about 20 minutes and watched a ton of air bubbles out of the radiator into the funnel. The air bubbles stopped, but when I slowly rolled from idle up to 1500 rpm, more bubbles every time. Is that normal or is it pulling air from somewhere? Once it got up to about 140 the bubbles seemed to be constant and the funnel filled with more coolant, about half way. I shut it down as I didn’t want another coolant geyser. temp gauge got to about 140, coolant temp in the funnel was also close to that.
I should add that I started with no coolant in the funnel and it climbed to about 1/2 full. As it’s cooling the funnel is empty and sucked back into the radiator.
After reading most of everything here were it in my hands I would do two things next. With it stone cold fill it with water and 4" blocks under front tires, keeps the air moving up and out. Let it set 1/2 hour then put a pressure pump on the Rad and pump it up to 18lbs. Watch the gauge and see if it drops. This will tell me if it has any internal gasket leaks. Next I'd take my drop light and move it around on one side of the Rad and from the other follow it with my eyes and look for contact of the tubes in the Rad. In other words, making sure I have full air flow through the Core. I have found large spaces where those cheap offshore alum rads come with factory air blockage. That will drive you nuts. Another thing is check Exhaust temps. Lean fuel makes for too much heat and will show up in exhaust temps before it blows over.
Just a guess, and maybe you’ve had it magna-fluxed , but is there a crack in the head(s) or block? Run a compression check after it’s done puking?
Rad pressure test will imply a crack as well. I would next do a leak down test before a cranking compression test. If you have a leaking head gasket it will tell you where it's at and whether or not it leaks into the water jacket.
My recommendation is to go buy or rent a "combustion gases tester" and test at the radiator for , well, combustion gasses. If the test is unfortunately positive, before you take the engine apart disconnect all coolant hoses coming from the engine (like heater and radiator hoses) and cap each hose with a PVC plumbing supply cap. On one of those caps you need to install a tire stem (shrader valve) so the engine can be pressurized with shop air. Remember to double-clamp the cap in the hose, then zip-tie a shop rag over the cap to prevent injury if the cap comes loose under pressure. The reason you want to do it this way is so you can pressurize the engine with far more pressure than the radiator/heater core can withstand.
It won't pull air in. It would push coolant out. The only way for non-coolant to end up in the coolant it a crack, or a bad gasket. It is not impossible, as early Hemi's are pretty thick, to have a deck crack. If there is a combustion gasses push, I would suspect a head gasket more than anything else.
I have suspicions about the size of the upper tank in the radiator, versus the overall capacity of the radiator. If it cools, but it pushes that much coolant up into the funnel on expansion, then there may not be enough expansion space in your system, as constructed. Remember, the early Hemi engines were used in full-size cars, with particularly large radiators.
A must for this is making sure that the timing is properly set, too. Late timing sends still burning mixture into the exhaust, driving up temperature there.
My friend had a water pump that rotated in the wrong direction. They make them for serpentine belts which go in one direction and the standard pulley ones that go in the other direction. It was driving my friend crazy until he figured it out.
Compression test is good. Gotta run and grab a leak down tester. Gonna do a leak down and a radiator pressure test next. I did run it again, tons of air again.... seems air is getting in somewhere
Take off thermostat and waterpump belt.top it off with water but leave thermostat housing of. Now get it running at idle ,maybe put some rpms And you should see witch side the bubbles are coming. Been using this trick many times.
Was the coolant moving while running cold? I would think with no thermostat in the system as the OP said that it would be moving immediately. Lippy
Yes moving immediately and bubbling into funnel immediately. Didn’t get hot cause no t-stat, but consistent bubbles that did not stop
the OP says lots of bubbles to be seen….The symptoms sound like an O/T car I owned noted for head gasket issues… The head gasket fails in such a way the combustion gases get into the cooling system…runs for a short time , the combustion gases pressurizing the system and coolant blows out when the cap psi rating is exceeded even though the engine is not real hot… Just saying….
Does your coolant smell like exhaust gas? If you have a compressor with a regulated output, you could make a fitting to replace a spark plug and with each cylinder at TDC firing you can check for bubbles in the radiator with the cap off.
Well there it is.... radiator test confirmed I have combustion gas in cooling system. Blue liquid to yellow damn quick....
This is when I'd do the leak down and listen for bubbles in the Rad. Do all 8. Don't just stop at the first sign of air leak. Let it tell you where the problem is, don't just go hunting.
If you can get access to a borescope, you can look for traces of coolant in all 8-cylinders. That will help you zero-in on a location. It is probably just a head gasket.
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