COOLANT BLEED (my experience)

[TANTO]

Lots of posts on this i know already. Done my coolant system change many times without an issue after my first time. I recently read Honcho and others struggles to get air out of the system - thus my "tip". I determined first time to not attempt to drain and fill in one work session. I raise the rear about 6" and simply put one bleed hose from the heater connection upward leaving all bleeders open except the thermo one and WAIT overnight. Point of this post is IMO it just takes overnight for the bubbles to find their way out. And then of course follow the SM bleed order (approx) a couple of times. No vac filling or heat cycles needed (antidotal warning). Obviously many mechanics have gotten the SM procedure to work as they can't wait overnight. But if you have to time, maybe try it? As a youth that was sprayed more than once with hot coolant waiting for a thermostat to open (or not!) this "mid/rear" engine fluid thing is understandably a bit stressful. At times I wish we had a "real" temperature/oil pressure gauges, but i've got enough on my list already.

 

[Chris_Lum]

I recently did a video on my channel for the coolant bleed procedure and found it relatively straight forward following the SM, especially for my first time. I think as long as you have tubes to attach to each bleed point and an adequate container to accept the amount of coolant that will displace, then it's not too bad. I bled mine in around an hour and that's with the uncertainty of never having done it before (not counting drain time since my radiator dumped most of it's coolant on public streets). In my limited (read: single) experience doing this, displacing about 1-2 gallons of coolant total out of the 2 front bleeders was key to getting all of the air out of my system. The rear bleeders only required maybe 1/2 gal total on my car. I'm wondering if those who have trouble with air pockets just aren't moving enough coolant to begin with.

 

[Old Guy]

I sort of followed the factory service manual along with guidance from Kaz. In particular, his suggestion to use a long clear hose set up to act as a siphon to a low mounted jug for the heater hose bleeder. This might theoretically be possible on the thermostat and rear firewall bleed points; but, I found keeping a long hose in place while turning those bleeders exceedingly difficult / impossible. I also found that I got a clear (no bubble) flow from those points fairly quickly. It was the heater hose bleed point that took forever to run clear. I do recall a comment from some other Prime member about not bothering with anything other than the heater hose bleeder (which would probably lengthen the amount of time it takes to finish the bleed). Kaz advocated for increasing the pressure on the 'fill side' by using an extension and a tall funnel to increase the hydrostatic pressure on the system. I did not do that because I did not have a suitable adapter for the expansion tank.

Raising the rear of the car may have a similar effect as Kaz's recommendation to elevate the filler and increase the hydrostatic pressure as the primary sticky point in the bleeding process appears to be the up and then down loop formed by the supply to the heater core.

simply put one bleed hose from the heater connection upward leaving all bleeders open except the thermo one and WAIT overnight

I am missing something here. On my na2 if you leave the back firewall bleeder and the radiator bleeder completely open with no hoses you are going to end up dumping the contents of the expansion tank on the floor because the tank is well above those two points.

 

[TANTO]

I would never question the Kaz/others mentioned method of using the extension funnel to get the job done quick. But, IF you can split your work sessions up you certainly can get a great result without it and without the messy bleed hoses IMO. I mispoke on the bleeders – let me start over: 6” or so high in the rear gets the air to leave the bottom hard pipes. Put a hose on the heater connection up a foot or so and tape the upper end to the underside of the hood – leave open and forget. Fill the tank a good two inches above max level. Open all bleeders. Be ready with wadded up paper towels at the firewall bleeder and thermo bleeder as they will bleed pretty fast. Likely not seeing anything at the radiator, close that for the night and open in the morning and then close when it flows. Re-bleed the firewall (this should be THE big burp), top fluid and then re-bleed that one again, then thermo, firewall and thermo again. I don’t think the exact sequence in the SM is needed –just hit them all 2-3 times. You will have a bunch of fluid in your heater connection to drain. I personally pop the cable off the heater valve and tape the valve open - thus i don't have to mess with the dash unit as i likely will have my battery disconnect switch open. I have not found it necessary to bleed much fluid at all. It’s my contention that if you let the system sit for some time the air does migrate on it’s own to just up under the bleed fitting, so a small-ish burp will do. I’m ordering one of those extension funnels for my front engine cars – very nice. We are actually kind of lucky in that with our mid-engine set up we can fill all the way with the thermostat closed and engine off. Not an expert – needed this to-do list for myself and thought I’d share.

 

[Chris_Lum]

I sort of followed the factory service manual along with guidance from Kaz. In particular, his suggestion to use a long clear hose set up to act as a siphon to a low mounted jug for the heater hose bleeder. This might theoretically be possible on the thermostat and rear firewall bleed points; but, I found keeping a long hose in place while turning those bleeders exceedingly difficult / impossible. I also found that I got a clear (no bubble) flow from those points fairly quickly. It was the heater hose bleed point that took forever to run clear.

Can you expand why you found it hard to turn the bleeders with a hose on it? Is it because the hoses were coiled up?

As far as getting a clear flow at the heater hose quickly, that's what I was kind of alluding to when i said enough coolant needs to be displaced. I found that the heater hose had the least restriction (I have old rubber cap setup vs the newer bleeder fitting setup) and just flowed coolant like crazy before even a drop of coolant even ran out of the radiator bleeder so once that happened, I grabbed some hose clamps and pinched off the heater hose bleeder tube and bled the others and circled back to the heater hose after the others were bled a bit. I cycled through all 4 bleeders a few times just to be sure. I found that A LOT of air came out of the heater hose bleeder after the rear bleeders had bled out air.

My entire bleed starts at 7:26 but at 12:48 is when I start to bleed the heater hose for the second time.

For me, the only bleeder I had an issue with is the radiator since there's no fitting there and I failed to watch Richard's (lap of the world) video where i think he installed an aftermarket fitting onto his koyo, which is an amazing idea. Next time i do a flush, I'm going to replace the radiator bleeder plug with a valve/fitting so i can regulate coolant flow better out of that port.

I have not found it necessary to bleed much fluid at all. It’s my contention that if you let the system sit for some time the air does migrate on it’s own to just up under the bleed fitting, so a small-ish burp will do. I’m ordering one of those extension funnels for my front engine cars – very nice. We are actually kind of lucky in that with our mid-engine set up we can fill all the way with the thermostat closed and engine off. Not an expert – needed this to-do list for myself and thought I’d share.

I corrected my earlier post where i misquoted how much fluid i displaced out of the front 2 bleeders after rewatching my video. I estimate i only did about 1-2 gal max out of the front two bleeders total. I used the funnel extension and raised the rear when I did it. All worked out fine. I think the tradeoff of time and having your car sit over night is spilled coolant, but depends on which you feel is the lesser of the two evils. I could definitely do it cleaner with a lot less spillage now that I know what I'm doing and what to expect. The hoses and directing them into large capacity containers are really key to being able to take your time and get all the air out vs rushing to close the bleeders because you're creating a mess.

 

[Old Guy]

Can you expand why you found it hard to turn the bleeders with a hose on it? Is it because the hoses were coiled up?

The bleeders on the water pipe (rear firewall) and the thermostat cover are in fairly tight spaces. Depending on the wrench you are using you might only get 90 deg of rotation before you need to lift and re position the wrench to open the bleeder more. Opening them enough to get a good flow where you can observe the absence of bubbles with the hose attached was difficult. Most of the time the hose popped off as I was rotating the bleeder. In the end I opened the bleeder and then shoved the hose on to collect about 1+ l of coolant and then fumbled to tighten the bleeder after doing the collection so I ended up with a fair amount of spillage. I was using clear vinyl tubing for my bleed hoses and it was fairly cool when I did the bleed process so the hoses were definitely not cooperative in terms of flexing as I rotated the bleeders.

I followed Kaz's method. He starts off with the thermo cover; but deviates by then moving to the radiator, then the heater core, then the water pipe and finally a repeat bleed at the thermo cover. His big deviation is doing a repeat bleed(s) at the heater core bleeder . He heat cycles the engine and then checks the heater core bleeder for air. Perhaps because I used a vacuum refill tool I had less air in the system than normal because I found that the thermostat cover, radiator and water pipe bleeders ran free of bubbles very quickly. It was the heater hose bleeder that had chronic bubbles.

I found that it took a couple of heat cycles before the coolant stream from the heater core ran completely bubble free. Given the way that the supply for the heater core loops up and then down I think it is no surprise that it is a chronic location for trapping air bubbles and you probably need flow through the heater core to dislodge the bubbles and the only way you get flow is after the thermostat opens up. Looping the bleed tube up high and then down into the catch can

 

[Chris_Lum]

The bleeders on the water pipe (rear firewall) and the thermostat cover are in fairly tight spaces. Depending on the wrench you are using you might only get 90 deg of rotation before you need to lift and re position the wrench to open the bleeder more. Opening them enough to get a good flow where you can observe the absence of bubbles with the hose attached was difficult. Most of the time the hose popped off as I was rotating the bleeder. In the end I opened the bleeder and then shoved the hose on to collect about 1+ l of coolant and then fumbled to tighten the bleeder after doing the collection so I ended up with a fair amount of spillage. I was using clear vinyl tubing for my bleed hoses and it was fairly cool when I did the bleed process so the hoses were definitely not cooperative in terms of flexing as I rotated the bleeders.

I followed Kaz's method. He starts off with the thermo cover; but deviates by then moving to the radiator, then the heater core, then the water pipe and finally a repeat bleed at the thermo cover. His big deviation is doing a repeat bleed(s) at the heater core bleeder . He heat cycles the engine and then checks the heater core bleeder for air. Perhaps because I used a vacuum refill tool I had less air in the system than normal because I found that the thermostat cover, radiator and water pipe bleeders ran free of bubbles very quickly. It was the heater hose bleeder that had chronic bubbles.

I found that it took a couple of heat cycles before the coolant stream from the heater core ran completely bubble free. Given the way that the supply for the heater core loops up and then down I think it is no surprise that it is a chronic location for trapping air bubbles and you probably need flow through the heater core to dislodge the bubbles and the only way you get flow is after the thermostat opens up. Looping the bleed tube up high and then down into the catch can

Ah I see. Yes it helps to heat up the vinyl tubing to make it flexible. With the tubing pliable, you can even turn the tubing to further open the bleeders, once they're already cracked open of course. I heated mine up and laid them out a day before hand as mine were coiled into a 5" diameter bunch which was unmanageable to say the least.

As far as the order Kaz uses, that is indeed the correct order for the 4 bleeders, he just repeats, which i think we all agree is necessary. Interesting to hear that you still experienced air pockets even with a vacuum bleeder. I have one also but didn't even try to use it because my compressor is tiny so i just went all manual.

 

[TANTO]

I know i said i wasn't an expert, but I am a retired powerplant piping engineer having designed dozens of piping systems all needing to be bled at start-up, thus my post. Although i've sometimes found things don't always transfer directly to my cars! While in theory the vacuum method should work but in practice we always use pressure to "burp" a system. No matter your procedure, the hose up from the heater bleed is ideal as the bubbles simply go out the top of the tube -no muss no fuss and it takes one of the bigger variables off the table. Way back for a moment i was thinking about doing this with all the bleeders which is sometimes done on stubborn industrial systems, but thats just not needed IMO. As stated above getting these bleeders open enough to flow yet not leak around the threads is a fine line, but certainly doable. One could put teflon tape on the bleeders eliminating the thread leak point, use hoses on all the bleeders turning up a couple of feet and the system would bleed itself - whoops - over analysis alert!

 

[Old Guy]

It occurred to me that my experience with the need for extensive bleeding might be in part due to the fact that I did a hose replacement. I also remember that some owners said they did not bother with the block drains. I didn't do the front block drain; but, I did the back block drain which is lower on the engine (and easier to access) and from the measured amounts that I collected I think I had the cooling system pretty much empty. As a result I may have had more air trapped in places than would occur with a normal cooling system flush.

 

[Wild Turkey]

Thanks for the heads up as I think I'll be doing my hoses this winter so it sounds like I'm down for a much tougher bleed this time. Both times I changed the coolant before, including block drains, but not changing hoses, I followed the SM exactly wrt order without much fuss, ~250-500 cc/port. After a short drive, I purged again but got almost nothing.

 

[Honcho]

It occurred to me that my experience with the need for extensive bleeding might be in part due to the fact that I did a hose replacement. I also remember that some owners said they did not bother with the block drains. I didn't do the front block drain; but, I did the back block drain which is lower on the engine (and easier to access) and from the measured amounts that I collected I think I had the cooling system pretty much empty. As a result I may have had more air trapped in places than would occur with a normal cooling system flush.

Same here, and I also did a complete engine overhaul, so the block was completely dry!