Radiator expansion tank constantly boiling

[Jolly Roger bus 223]

sorry to say but trust me i know???
you can have a bad head gasket letting exhaust into the coolant passage and bubble into your radiator and into the overflow tank without showing signs of being in the oil.
luckily that means most of the time? its just a failed gasket and not a warped or cracked head.
but if you are doing it yourself then you can check the heads yourself while they are off
if its a shop that you trust and know then follow there opinion as long as you trust them.
but yes it happens and i am just hopefully finishing a motor with the exact same issues.
and please dont waste money on the snake oil head gasket repair mess because it will clog and mess up the rest of everywhere coolant go s and be a bigger issue later.

[Jolly Roger bus 223]

trace your compressed air lines.
and see if any connect into the coolant system.
i have never messed with what you have but i have never heard of an air compressor connected into a coolant system?
i could be wrong but a check valve should not be the only thing seperating them?
seperate coils YES but not air in the cooling unless i read something wrong.
side note
i just learned that this special pain in the butt car i have just spent the last 7 weekends on has a power steering fluid cooler on it????
i know i got out of it for awhile but really a fluid cooler for power steering?
alot of other special mess that i didnt know existed.
sorry.
wish you luck.

[cadillackid]

roger - the compressor head has engine coolant lines going through it for cooling the compressor.. this will be on the Bendix Tu-Flo 500,550,7xx series compressors..



the thing about the air compressor leaking into the coolant is that it will do it even after you shut the engine off till the air pressure drops out of the wet tank..



if you can make your coolant bubble at id;le with the cap off. then open up your air drain valves on all 3 tanks while the bus is idling and see if without any air pressure being built up you still incur the bubbles.. if theres no change then chances are you blew a head gasket, cracked a head, etc..



the coolant lines can go into the sides or ends of the compressor head and are easy to spot.. on mine they are hose fittings that you could remove and then pressurize to see if you get bleed down indicating a leak then you can assume a problem..


you can also pump the air system up to capacity, place a hose on each end of the compressor head and put the 2 ends down in a bowl of water and see if it bubbles.. you can start and run the compressor for a short period for testing without harming it having no coolant in the head..



running the temp gauge off the scale usually wont damage a compressor head.. however it can and does damage the engine.. head gasket, head, etc.. and the only way to truly know is to do a cooling system leakdown test and if the water doesnt show up in a heater loop or radiator or other known place then most likelyits going inside the engine someplace..



ive seen head gasket blows so bad that the engine hydrolocks after the leakdown test..

[mmoore6856]

Originally Posted by cadillackid

roger - the compressor head has engine coolant lines going through it for cooling the compressor.. this will be on the Bendix Tu-Flo 500,550,7xx series compressors..



the thing about the air compressor leaking into the coolant is that it will do it even after you shut the engine off till the air pressure drops out of the wet tank..



if you can make your coolant bubble at id;le with the cap off. then open up your air drain valves on all 3 tanks while the bus is idling and see if without any air pressure being built up you still incur the bubbles.. if theres no change then chances are you blew a head gasket, cracked a head, etc..



the coolant lines can go into the sides or ends of the compressor head and are easy to spot.. on mine they are hose fittings that you could remove and then pressurize to see if you get bleed down indicating a leak then you can assume a problem..


you can also pump the air system up to capacity, place a hose on each end of the compressor head and put the 2 ends down in a bowl of water and see if it bubbles.. you can start and run the compressor for a short period for testing without harming it having no coolant in the head..



running the temp gauge off the scale usually wont damage a compressor head.. however it can and does damage the engine.. head gasket, head, etc.. and the only way to truly know is to do a cooling system leakdown test and if the water doesnt show up in a heater loop or radiator or other known place then most likelyits going inside the engine someplace..



ive seen head gasket blows so bad that the engine hydrolocks after the leakdown test..

all he said here is correct also if you suspect the compressor head to causing the bubbles start it watch for bubbles while its running and bubbling take the output air line off the compressor see if it quits or slows way down.

[cadillackid]

Originally Posted by mmoore6856

all he said here is correct also if you suspect the compressor head to causing the bubbles start it watch for bubbles while its running and bubbling take the output air line off the compressor see if it quits or slows way down.

good call on taking the air output line off the compressor..

[Jolly Roger bus 223]

you learn something new everyday.
now i wanna know?
compressed air creates hot air that creates moisture which means filter dryer and auto drain/purge valves
split radiator?

[cadillackid]

you lost me.. compressed air should never end up in the coolant loop.. the air dryer is between the compressor discharge and the wet tank.. it purges moisture out.. the OP's cap should boil before the radiator is split open due to an air leak if thats what you are referring to..

[Prince408]

Originally Posted by mmoore6856

all he said here is correct also if you suspect the compressor head to causing the bubbles start it watch for bubbles while its running and bubbling take the output air line off the compressor see if it quits or slows way down.

I'm also going to try this out. I have already drained the tanks and the problem goes away.

[CHEESE_WAGON]

Originally Posted by Danjo

When you’re done you need to purge the air from the coolant system by drinking it to temperature and gradually adding the coolant back in.

Folks, please check your posts before submitting... This seems like a fairly benign error, but could have fatal results if taken literally.

OP - DO NOT drink your antifreeze, in case you are wondering...

[FlackShack]

Kinda late to update this for everyone. But there were several things that happened, so I'll just start from the beginning.

Before taking the bus on its maiden voyage back to MN, I consulted several mechanic shops in town about the coolant bubbles. After looking at the reservoir and engine, they said not to worry about it. I drove it around a lot too, and after replacing those 7 gallons of coolant it never overheated.

I did notice that I was missing several quarts of oil though since my dipstick was around the "Fill 2 quarts if low" mark. Which must have happened after running the engine w/o coolant for awhile - some of the oil must have burned off. It took 4 quarts of oil. Oil pressure stays within spec at 55-65 psi.

I continued to run the bus for awhile afterwards and neither the coolant nor the oil has discolored from the fluids mixing. Water temp stays within 200 degrees at highway speeds (70 mph) w/ the fan clutch engaging.

The reservoir still bubbles but I believe the reason for this being something the previous owners had done. I compared the OPs pictures from their first post to the reservoir installed on my bus, and the tanks are completely different. There is also a hose leading from the top of my engine block directly into the top of the expansion tank. There is coolant running through this high at a decent pressure which I believe to be the reason for the bubbles in the tank - I can see it shooting jets of coolant into the expansion tank.

I think this was supposed to be my return line, but it must have been modified?

Who knows. The bus is back to running great though.

[mmoore6856]

that line on top of the engine that connects probably had a valve in it instead of a line to bleed the air out of the engine when refilling. it is defeating your engine of being able to raise the water pressure (thus raising the boiling point) you need to see a good mechanic that is familiar with that cooling system and find out. overflow tanks should be after the pressure cap

[Booyah45828]

His tank is likely pressurized, and is therefore a degas tank, and not an overflow tank. That's how most FE transit buses are.

That hose coming from the engine into the tank is by design. It provides a path for air that could be trapped in the engine, to vent into the degas tank. I typically see them submerged with coolant though, so the fact that yours is squirting into the coolant level tells me you should check and make sure your coolant isn't low. It's possible you have one from the radiator too, and maybe someone flipped which barbs the hoses attach to.

[FlackShack]

Yeah, next time I start it up again I'll take some pictures and a video of the coolant being sprayed into the expansion tank. I know it isn't low because I can open the cap and see the coolant.

Like the image that the OP posted, I have the same hose indicated in red going from the top of the block to the back of my tank. But we have different tanks.

[FlackShack]

I should mention that the point where this hose is attached to the rear of the tank is higher than the line where the max fill for the coolant is.