Radiator air bleeding

Dr.Jeff

True Classic
In the "what did you do today" thread @Dan Sarandrea (Phila) said the following about burping the air out of his radiator:

"I am going to have to come up with a better venting/draining arrangement for burping as I HATE that burping results in a mess up in the radiator compartment and drips where it wants to drip, which is rarely in the drain pan!"
"I follow Jay Leno's burp technique that he uses on his Miura, do it while the cooling system is up to full temp and while the engine is running. That way the system's own internal pressure helps to expel the air. If you burp while the system is cold and not running, under certain circumstances I think opening the burp plug could let air in."

I don't intend for this to be the old debate about the X's cooling system design faults, or even question why a closed system should require repeated bleeding. But I'd like to throw around some ideas for better burping, without the mess Dan describes.

On one of my X's the original rad bleed bolt had been replaced by a prior owner with a simple plug. When I went to look for a suitable replacement bleeder valve I discovered that BMW radiators use the same size thread/diameter bleeder. Theirs is a different design; brass with a center hole for the air path and a slot for a screwdriver rather than the hex socket head. Looks like this:
71QzvoX11DL._AC_SL1500_.jpg


I know from experience that it is easy to use and doesn't tend to get stuck or clogged. Plus they can be found easily for a couple of dollars online. So that's what I got to replace the missing one.

Not that this is any different in terms of what Dan is talking about. It will still allow a bit of fluid to leak when burping the system, running down the rad and spreading a mess everywhere. But in the process of searching for a replacement I found the bleeder's thread size/pitch [M10 (1.0) if I recall correctly - I can verify that]. So after reading Dan's comment today I got thinking how to improve the burping process and eliminate the mess. How about replacing the bleeder valve with a M10 (1.0) fitting with a hose barb, run a hose from it to the bottom of the rad, and add a common valve there. Then to bleed it you work from below instead of above, and any fluid will drain directly into your catch pan. Or if you prefer to not work from below, then install a valve with a hose barb directly into the rad's opening and then route the drain hose to the bottom. For that matter you could route the hose and valve to any convenient location to make reaching it easier - so long as your air path allows the air to escape before the fluid does. There is ample room above the X's bleed valve location to allow any changes in fittings, etc. And if you want to get fancy with either approach you could install corresponding fittings to attach a hard line rather than a hose, everything else being the same.

This seems very easy to do and would prevent the mess when burping the rad. Thoughts?
 

kmead

Old enough to know better
In the "what did you do today" thread @Dan Sarandrea (Phila) said the following about burping the air out of his radiator:

"I am going to have to come up with a better venting/draining arrangement for burping as I HATE that burping results in a mess up in the radiator compartment and drips where it wants to drip, which is rarely in the drain pan!"
"I follow Jay Leno's burp technique that he uses on his Miura, do it while the cooling system is up to full temp and while the engine is running. That way the system's own internal pressure helps to expel the air. If you burp while the system is cold and not running, under certain circumstances I think opening the burp plug could let air in."

I don't intend for this to be the old debate about the X's cooling system design faults, or even question why a closed system should require repeated bleeding. But I'd like to throw around some ideas for better burping, without the mess Dan describes.

On one of my X's the original rad bleed bolt had been replaced by a prior owner with a simple plug. When I went to look for a suitable replacement bleeder valve I discovered that BMW radiators use the same size thread/diameter bleeder. Theirs is a different design; brass with a center hole for the air path and a slot for a screwdriver rather than the hex socket head. Looks like this:
View attachment 32787

I know from experience that it is easy to use and doesn't tend to get stuck or clogged. Plus they can be found easily for a couple of dollars online. So that's what I got to replace the missing one.

Not that this is any different in terms of what Dan is talking about. It will still allow a bit of fluid to leak when burping the system, running down the rad and spreading a mess everywhere. But in the process of searching for a replacement I found the bleeder's thread size/pitch [M10 (1.0) if I recall correctly - I can verify that]. So after reading Dan's comment today I got thinking how to improve the burping process and eliminate the mess. How about replacing the bleeder valve with a M10 (1.0) fitting with a hose barb, run a hose from it to the bottom of the rad, and add a common valve there. Then to bleed it you work from below instead of above, and any fluid will drain directly into your catch pan. Or if you prefer to not work from below, then install a valve with a hose barb directly into the rad's opening and then route the drain hose to the bottom. For that matter you could route the hose and valve to any convenient location to make reaching it easier - so long as your air path allows the air to escape before the fluid does. There is ample room above the X's bleed valve location to allow any changes in fittings, etc. And if you want to get fancy with either approach you could install corresponding fittings to attach a hard line rather than a hose, everything else being the same.

This seems very easy to do and would prevent the mess when burping the rad. Thoughts?
If you can find a 90° hose barb with that thread you could be in business. The ones I looked at were all straight which could allow you to have it come into the frunk and do the deed in there.


I spoke too soon:

One like this would be ideal if the offset matched the header tank of the radiator:
 
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tigeravg

True Classic
I want a spring loaded, plunger type bleed valve that has a simple 90 degree lever I can reach in and press... PSHHHT...done.

Also, I get what Jay is say'n... That being said...
I place the rear end real high (slope on my driveway) and let it heat cycle a couple times.The air should go to the highest point (catch tank, where I want it to go). Then while still in this position, I bleed the rad. I level out the car while still hot and running, bleed one more time. Call it done. Works for me. Just say'n
 

kmead

Old enough to know better
Funny I have always done it the opposite way, nose high and bleed the air out of the high point of the radiator since that air can’t get out of the radiator any other way.

Whatever gets it done.
 
Funny I have always done it the opposite way, nose high and bleed the air out of the high point of the radiator since that air can’t get out of the radiator any other way.

Whatever gets it done.
That is how I've always done it for the same reason as Karl said and it has never been a big deal to get the air out.
 

Dr.Jeff

True Classic
I want a spring loaded, plunger type bleed valve that has a simple 90 degree lever I can reach in and press.
Might be fun to do some research to see what's available. Spring loaded valves exist. But even if there's a 'regular' type valve that can be fitted to the top and allow a hose/tube to extend to the bottom. So the bleeding can be performed from the top instead of below, but have the fluid drain at the bottom.
 
After I had my radiator recored, I had them replace my bleed screw, which had a crack, with a "T handle" type valve like they often used to use for radiator drains. I find it very easy to use - no tools required. Just turn the T handle to open or close. Works well with the low clearance in that spot as you only need to place your hand on it.
 

JimD

Waiting for Godot...
Moderator
Since I just replaced the radiator in my 86 the other day, I will tell you what I usually do.

I park the X flat. Open the cap on the reservoir, set heater valve to full open and open the bleed valve at the rad. With the engine off, I pour coolant into the reservoir until it runs out of the bleed valve at the front. Then I shut the bleed valve and start the car and turn the fan to high. I watch the coolant level in the reservoir and add as needed. After the car warms up I open the bleed valve until it dribbles and then check the res level again. Button it all up and make sure the radiator fan comes on. Then I will check the bleed valve after a couple drives. I can't say that I have ever encountered a lot of air at the bleed valve on follow up checks.

I have tried nose up, nose down, etc over the years and have never found a significant difference compared to bleeding it flat. YMMV :)

Yes, I have had an X with LOTS of air every time I bled it, but it was usually a compromised radiator causing the issue. My 85X was like this when I bought it. Fortunately, BobG was issuing his first run of aluminum reproduction radiators at that time. I bought 2 and put one in my 85 at a few years ago and then put the second one in my 86 this week. I have some open shelf space now. 👍
 

Dr.Jeff

True Classic
I had them put a 1/8" NPT fitting in for the bleeder -> lots of options.
Exactly. A 1/4" NPT tap requires a 27/64" hole (.4218"). If the stock bleeder is M10 (.3937"), then it wouldn't be difficult to bore it out so a 1/4" NPT tap could rethread it. With radiators being soft (brass or aluminum) it would drill and tap easily. A NPT thread allows any type of valve as you say.
 

Dr.Jeff

True Classic
I can't say that I have ever encountered a lot of air at the bleed valve on follow up checks.
Yes, I have had an X with LOTS of air every time I bled it, but it was usually a compromised radiator causing the issue.
I keep wondering the same question. Why do some X owners need to constantly bleed air out of their cooling systems, while others never do. At the beginning of this thread I said I do not want this to become that debate again, and I don't. So perhaps I should not have just mentioned it. But my intent is not to begin the discussion, only to relay that I keep wondering the question...from purely a mechanical perspective. E.g. is there something that I should do or not do to avoid the problem.
 
Exactly. A 1/4" NPT tap requires a 27/64" hole (.4218"). If the stock bleeder is M10 (.3937"), then it wouldn't be difficult to bore it out so a 1/4" NPT tap could rethread it. With radiators being soft (brass or aluminum) it would drill and tap easily. A NPT thread allows any type of valve as you say.
My radiator guy had to solder in a new bleed fitting because the old one had a hairline radial crack. Since we had a choice on what to replace it with, we went 1/8" NPT because lots of stuff will screw into it (Tap size is 21/64). If you are retapping the existing fitting, 1/4" NPT should be a good choice.
 

Datsun Guy

Low Mileage
I used a vacuum coolant filler, from Amazon after replacing the radiator. Evacuates the system using compressed air to create vacuum, all the hoses get sucked flat. Put the hose in a bucket of coolant, and it sucks it in. Got no air from bleeder, as there was no air in there when the coolant went in. Runs cool, no issues. Well worth the approx $70.00
 

SteveG

Low Mileage
I used a brake banjo fitting into the top of my radiator, with flexi pipe down to ground level. The normal fitting where the hard-line brake pipe goes has a 10mm bleed nipple fitted. I bleed into a clean container, then re-use the coolant to top up again.
20200630_082456.jpg
 
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