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Degas Cap Spewing

4K views 26 replies 10 participants last post by  DeadBrown 
#1 ·
I've got a '96 7.3 f350, I just did a coolant flush and put in a thermostat (it didn't have one before). I can't say that it "just started" because I just bought the thing. Once the engine warms up after a little driving, ~5 miles, the degas bottle just start pouring fluid out of the cap. It's not really hot, and the cap comes off with a small hiss when i pull it without letting the engine cool much. I had the heater on to get the heater core to cycle the new fluid, but the air comes out cold. I don't notice any diesel or exhaust smell in the anti-freeze. I feel like the heater core is clogged, but my dad thinks I overfilled the system, but the degas was pretty low once it was done and I filled it to the cold level line on the bottle. Any ideas? Thanks
 
#2 ·
No thermostat? Sounds like the previous owner was hiding something. Coolant puking from the degas bottle is caused by excessive pressure in the coolant system. Typically caused by combustion gases in the coolant.
 
#5 ·
I've had to refill/flush my coolant probably 5 times and every time I fill it til the full level on the degas bottle.

I'll take it for a drive and yes it will push fluid out of the cap since it is working the air out of the system. Turn the heater on, watch the gauges and drive it til it fully warms up and forces the air out. You will see a big spike in temperature and then it will come down once the coolant gets flowing. Have a gallon or two of coolant/ distilled water handy while driving because you will need to top it off.

These motors take a while to get warm so be patient and make sure when it purges the air that you fill it up. The heater will blow warm when everything settles.
 
#7 ·
What brand t stat did you use?
 
#8 ·
I just swapped the cap, no more degas puking, but not it looks like I've gotta replace the water pump seal, tiny bubbles and hissing from the top. I swear it's like this guy hadn't even seen a car before, the type of shoddy repair jobs he did.

Oem tstat and cap.

I'll report back if any problems other than the pump seal show up.
 
#10 ·
#9 ·
It helps to drill a very small hole in the thermostat. The air caught in the block will slowly piss through to the rad side.

If you're gonna change your water pump gasket, make sure you do a partial fill with the heater hose off the pump, that will help as well.

After taking an hour to get the fan clutch off due to rusty threads, I strongly suggest you put anti-seize on them!


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#12 ·
So that's not your water pump gasket leaking, that's your front cover. It's a much bigger job.


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#14 ·
Okay, so, replacing the water pump seal fixed the leak at the top of the pump between it and the case, but then it made me realize that my real problem was the hurricane from the weep hole. Another pump and gasket later and no more leak! Well... No more coolant leak at least... Haha
 
#15 ·
Ok, I'm reopening the case on this stupid thing. I've done a flush, replaced the degas cap, the degas bottle, put in a new fan shroud, replaced the water pump, and the thermastat and the damn thing is still pumping fluid from the degas bottle! I start running it and once it warms up it dumps a gallon and half of coolant, then I can run it and run it and no problems until it cools off again, in which case the cycle repeats. It's consistently a gallon and a half once per run, there is no coolant in the oil or vice versa, so I don't think it's the heads. Does anybody have a clue as to how to exorcise this damn demon?!
 
#17 · (Edited)
Didn't realize that I was in 7.3 zone...
 
#18 ·
Def has problems if the OPs 97 has a egr cooler.

Take the thermostat out and see if it still happens.

Do you refill it after it pukes and is warm and everything is ok till another heat up cycle? Or do you just keep driving it down a gallon with no recurring issues?

Does it push coolant like it's overheating or just blow it all out at once? Under load when it blows out?

Are you using any kind of monitor to watch temps? OBS computer doesn't have a coolant temp monitor but you can watch actual oil temp to see how hot things are getting.
 
#19 ·
I refill the gallon and a half and it's fine until the next heat up cycle. I don't think it's overheating because it'll be fine for a good while after the refill, won't lose another drop. It's not under any load. I'm not using a monitor right now, but when I was I wasn't getting any readings back from it. I'm not getting any codes. And like I said, I don't think it's heads because I'm not getting any oil or coolant mixing.
 
#20 ·
What brand did you use for all your parts.
 
#23 ·
Did you notices any excess rtv in the cooling system.
 
#24 ·
It can still leak pressure into a water passage and you'd never see any oil/water mixing.

I would take the thermostat completely out and see what happens. You might have to gut the thermostat to leave the rim in to make the o ring seal but a thermostat is not a very expensive try.
 
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