Bleeding cooling system question

#1

I drained the cooling system and refilled it with approx. 75% water and 25% antifreeze. We get some cold weather in NC but it never gets crazy cold.

I opened the bleeder screw several turns and started filling the expansion tank, per Bentley. The tank got full (just over the “full” mark) and nothing drained from the bleeder screw. I started the engine and squeezed the hoses as it warmed up but nothing from the bleeder screw. I then jacked-up the right side of the car but nothing. A friend said this would help bleed air out of the system. As it got up to temp, all hoses were hot so the thermostat had to be open and the level in the expansion tank rose up to the top of the filler neck. I let it get just past the middle on the stock gauge before turning on the fan, which brought the temp back down to just below the middle, and the coolant level dropped some. Again, nothing ran out of the bleeder screw.

I let it sit overnight and did the same things, and got the same result. Nothing from the bleeder screw.

I’m doing an 8 hour enduro with only a warm up session. Should I be concerned that there’s air in the system? I don’t want a cooling issue during that race.

Any thoughts?

Thanks,

Carter

#2

[quote=“Carter” post=74855]I drained the cooling system and refilled it with approx. 75% water and 25% antifreeze. We get some cold weather in NC but it never gets crazy cold.

I opened the bleeder screw several turns and started filling the expansion tank, per Bentley. The tank got full (just over the “full” mark) and nothing drained from the bleeder screw. I started the engine and squeezed the hoses as it warmed up but nothing from the bleeder screw. I then jacked-up the right side of the car but nothing. A friend said this would help bleed air out of the system. As it got up to temp, all hoses were hot so the thermostat had to be open and the level in the expansion tank rose up to the top of the filler neck. I let it get just past the middle on the stock gauge before turning on the fan, which brought the temp back down to just below the middle, and the coolant level dropped some. Again, nothing ran out of the bleeder screw.

I let it sit overnight and did the same things, and got the same result. Nothing from the bleeder screw.

I’m doing an 8 hour enduro with only a warm up session. Should I be concerned that there’s air in the system? I don’t want a cooling issue during that race.

Any thoughts?

Thanks,

Carter[/quote]
The way to beat cooling system bleeding problems for all time is to drill a tiny hole in the thermostat near it’s top. Use the smallest bit you own because the hole will allow coolant to bypass the radiator. The hole will allow air to move around so you will be free to bleed the system even w/o waiting for the tstat to open.

The “hose is hot” business can fool a person. It’s spooky that you couldn’t get water out of the bleeding port. Might want to do bleed the system again, but this time wait even longer to be absolutely sure the tstat opened.

Checking the bottom of the radiator to see if it’s hot should be a pretty good test of the tstat being open.

#3

That seems odd, did you put the cap on and allow system to build pressure while the screw is open? If you have pressure it seems something has to come out, whether air or water.

Having screw open while filling may have allowed air to escape as you fill (interesting idea, never done it that way) so you may be fine but understand why you want to be sure.

#4

I had this issue and it turned out that my bleeder screw hole in the thermostat housing was just clogged. Completely remove it and shove something in there to make sure it is clear.

#5

I’ve not seen that before but it’s a really good thought.

#6

Actually you want to drill a 3/16" hole in the thermostat flange where the arrow points up. Install it up. Two benefits…the system will bleed while you are filling it, no mote bleeder screw. Second, it allows water to bypass the thermostat to the temp sender…if the thermostat sticks and you watch your gauges, no blown motors from overheating.

#7

Sorry to revive an old thread. Drilled a 3/16" hole per Chuck’s recommendation. No bleeding at all with this in place? Do you need to open the bleed screw while filling and close it after?

#8

Just fill slowly and you’ll have no air. You can squeeze the hoses while filling to check.

#9

I hate to find myself in disagreement with Chuck because he’s been doing this a long time, but I think you still need to bleed the system. Normally to bleed the system the coolant needs to be hot enough that the tstat is open. A little hole in the tstat means it’s “a little” open, so you don’t have to wait for the engine to get hot.

If you don’t bleed at all there’s going to be air trapped because there’s no way for it to exit. The bleed valve is above the radiator return. A closed tstat would block off the engine from the bleed valve so any air trapped in the head wouldn’t be able to get to the bleedvalve.

#10

The easiest way to fill the cooling system is to remove the hose at the thermostat that connects to the driver side of the radiator. after removing the hose at the thermostat, loosen at the radiator then rotate and fill the radiator until it overflows. Then fill the engine block side of the cooling system through the exposed thermostat housing opening. With this method, you fill the block side and the radiator side of the cooling system without a need to bleed at all.

#11

I wound up cracking the bleed screw anyway, and got a lot of bubbles, so apparently I didn’t fill it slow enough. Very handy, though, not having to wait for the car to get hot.

Rich, I’ll have to try it your way next time.

#12

Never had to open bleed screw in 10 years of filling after drilling hole in t’stat. YRMV:laugh:

#13

No doubt, Chuck. I’m sure I wasn’t filling it as slowly as I should have, or otherwise did something else incorrectly. I had some very foamy bubbles come out for about five seconds, then all was well. Thanks for the tip on the 3/16" hole! “Next time”, I’ll try filling with Rich’s method. I like it because I don’t have to worry about how fast/slow I’m filling. I’ll probably still bleed it with that method, as I still don’t see how it’s possible to not get at least a little air in the system. Especially if I’m doing it, LOL.