Air in coolant?

Iceni John · July 11, 2023, 08:28:10 PM

My engine is now completely rebuilt and back in the bus after it ate a camshaft last year, but we can't put back all the coolant that we initially emptied out of it. We had drained about 30 gallons out into a big plastic tote bin, covered the bin with its lid, and didn't touch it until we refilled the engine recently. It all went well until the last 2.5 gallons that just won't go in. I've replaced the old coolant booster pump with a new Groco CP-25 pump, we've driven the bus locally (but not on the freeway at high speed) for an hour or more, then today I had the engine at Fast Idle at 1225 RPM for about an hour with both the heaters on, and it still won't take these last 2.5 gallons. We're assuming the air is in the heater loop: when I closed the coolant loop's two isolating valves and disconnected the hoses on the old booster pump before removing it, only about a pint or two of coolant came out, much less than would normally sit inside 80 feet of 1" pipe to/from the front and inside the two heaters. Unfortunately there's no bleeder valve on either heater, but very little air was coming out of the bleeder on the coolant crossover pipe to the radiator.

Soon after I bought the bus I had ABC Bus change the coolant, and there was no problem getting any air out of the system at that time: we just ran the engine at about 1500 RPM for half an hour or so with the heaters on, and then we were good to go. Why is it such a problem to do this now?! Have we overlooked something important? All valves are open, the heaters are blasting out lots of heat, and there's a brand-new booster pump to move the coolant to the front and then back to the engine.

Any ideas, anyone? All sensible suggestions will be gratefully received!

Thanks, John

chessie4905 · July 12, 2023, 03:41:18 AM

The bleeder should be at the dash heater defroster at top line.

luvrbus · July 12, 2023, 06:13:31 AM

I use a shop vacuum to get the air out of the system since some of the bleeder valves are hard to get at,it works on the generator too,some of those little engine can be a real pain to get the air out

Iceni John · July 12, 2023, 10:37:42 AM

Quote from: luvrbus on July 12, 2023, 06:13:31 AM
I use a shop vacuum to get the air out of the system since some of the bleeder valves are hard to get at,it works on the generator too,some of those little engine can be a real pain to get the air out

Where do you connect the shop vac to? The radiator filler, or somewhere else? Do you use the shop vac when actually refilling the engine, or afterwards when the engine has taken all the coolant it can take?

I've heard from others about this shop vac method, but I was never clear about how it's actually done.

Thanks, John

lovetofix · July 12, 2023, 08:31:24 PM

Did the rebuilder test run/dyno the engine before giving it back to you? The engine can hold quite a bit of coolant down in the block even with the hoses disconnected.

Iceni John · July 12, 2023, 10:54:42 PM

Quote from: lovetofix on July 12, 2023, 08:31:24 PM
Did the rebuilder test run/dyno the engine before giving it back to you? The engine can hold quite a bit of coolant down in the block even with the hoses disconnected.

The engine was completely stripped down to a bare crankcase, and every piece was hot-tanked. There was nowhere for coolant to hide there! And yes, it was test-run for an hour or so on the work stand (after the entire fuel system had been pressure-tested). Besides, if coolant had managed to remain inside, then it wouldn't have been drained into the tote bin; our issue is that we cannot refill all of what was originally drained out.

John

luvrbus · July 13, 2023, 04:34:24 AM

Not being around Crowns much and not knowing the HVAC system setup,it could be a valve closed in loop or a booster pump is not working. If the engine is not running hot it has to be the HVAC system is air locked, I hook a wet/dry on the loop somewhere on the HVCA and suck the air out with the engine running, it doesn't take much vacuum to break the air lock if it is circulating with the valves open. The water pump on the engine circulates 65gpm so it will move coolant, another way to find a air lock is with a hand held IR thermometer find a cold spot with a hot spot with in a few inches of each other and sometimes just loosening a hose clamp in the area will start the flow. Not knowing your setup check the air compressor for overheating a lot of manufactures of the past would tie the air compressor into the HVCA loop and they would air lock, hope a rag didn't get into the system like Vans 8v92

tr206 · July 13, 2023, 04:35:13 AM

Just run it and keep a eye on the coolant level the if it's air will work it's way out.

Iceni John · July 13, 2023, 10:23:15 AM

Quote from: luvrbus on July 13, 2023, 04:34:24 AM
Not being around Crowns much and not knowing the HVAC system setup,it could be a valve closed in loop or a booster pump is not working. If the engine is not running hot it has to be the HVAC system is air locked, I hook a wet/dry on the loop somewhere on the HVCA and suck the air out with the engine running, it doesn't take much vacuum to break the air lock if it is circulating with the valves open. The water pump on the engine circulates 65gpm so it will move coolant, another way to find a air lock is with a hand held IR thermometer find a cold spot with a hot spot with in a few inches of each other and sometimes just loosening a hose clamp in the area will start the flow. Not knowing your setup check the air compressor for overheating a lot of manufactures of the past would tie the air compressor into the HVCA loop and they would air lock, hope a rag didn't get into the system like Vans 8v92

Thanks for those good suggestions! I will definitely use my IR thermometer on as much of the heater loop as I can reach. We checked the engine earlier but didn't find any anomalies there. The new booster pump is working well: it's rated at 17 GPM, and its hoses have as few bends as possible so its flow should be strong. I had my air compressor rebuilt, but it's not tied into the heater loop at all.

Thanks again, John

Iceni John · July 13, 2023, 10:27:12 AM

Quote from: tr206 on July 13, 2023, 04:35:13 AM
Just run it and keep a eye on the coolant level the if it's air will work it's way out.

Because the coolant surge tank's lower and upper level marks are only about 3" apart, I would have to stop and check its level quite frequently. If the coolant level drops enough that the Low Coolant Level sensor is exposed, the DDEC will shut down the engine.

John

Glennman · July 13, 2023, 12:54:14 PM

Quote from: Iceni John on July 12, 2023, 10:54:42 PM
The engine was completely stripped down to a bare crankcase, and every piece was hot-tanked. There was nowhere for coolant to hide there! And yes, it was test-run for an hour or so on the work stand (after the entire fuel system had been pressure-tested). Besides, if coolant had managed to remain inside, then it wouldn't have been drained into the tote bin; our issue is that we cannot refill all of what was originally drained out.

John

Not to speak for someone else, but I believe what was being said is that if the shop tested the motor for an hour, they probably put some coolant in it for the test. So maybe you received it with some coolant that was put in it after the rebuild. I'm not a mechanic, but it seems to me that if they are going to test a motor for an hour, it would need coolant for the test (?)

luvrbus · July 13, 2023, 01:31:00 PM

Quote from: Glennman on July 13, 2023, 12:54:14 PM
Not to speak for someone else, but I believe what was being said is that if the shop tested the motor for an hour, they probably put some coolant in it for the test. So maybe you received it with some coolant that was put in it after the rebuild. I'm not a mechanic, but it seems to me that if they are going to test a motor for an hour, it would need coolant for the test (?)

Those 2 strokes take 6 to 7 gals for engine alone

chessie4905 · July 14, 2023, 06:19:45 AM

Are you getting good heat at all heaters and defroster? Lots of air, little to no heat. If you have no heat at defroster, high spot in loop, that's where the air is.

Iceni John · July 14, 2023, 11:03:48 AM

Quote from: Glennman on July 13, 2023, 12:54:14 PM
Not to speak for someone else, but I believe what was being said is that if the shop tested the motor for an hour, they probably put some coolant in it for the test. So maybe you received it with some coolant that was put in it after the rebuild. I'm not a mechanic, but it seems to me that if they are going to test a motor for an hour, it would need coolant for the test (?)

We were running plain water through the engine while it was on the test stand. I wanted all that water drained out, including what was in the heat exchangers, but maybe some of it remained inside. If so, that may explain this discrepency. I'll check into this on Monday when I'm next at the mechanic's.

John

Iceni John · July 14, 2023, 11:04:38 AM

Quote from: chessie4905 on July 14, 2023, 06:19:45 AM
Are you getting good heat at all heaters and defroster? Lots of air, little to no heat. If you have no heat at defroster, high spot in loop, that's where the air is.

There's plenty of heat coming out of both heaters!

John