TheSamba.com :: View topic - Bleeding cooling system with seized radiator bleed screw

Tue Jul 01, 2025 12:25 pm

This AI stuff is getting annoying. Moderators, this will become a more prevenient issue going forward. One of you guys must be a tech nerd, fix it.

BK

Tue Jul 01, 2025 12:34 pm

1988M5 wrote: This AI stuff is getting annoying. Moderators, this will become a more prevenient issue going forward. One of you guys must be a tech nerd, fix it.

BK

meaning what, this whole post is a troll?

if it were anywhere else, I'd think it's an AI spoof but here in the land of the stereotypical cheap VW owner, I think it's very real.

Tue Jul 01, 2025 12:52 pm

Van den Broke wrote: Thanks for all the suggestions.

The drilling idea got me thinking - I could drill a small hole in the bolt and thread it for, say, a 3mm (stainless!) screw to bleed it.
If I were really lucky I could loosen the radiator and tip it forwards at the top so I could do the job without having to remove it.

When the van is warmed up the radiator is only hot on the lower third, which seems to indicate that's the coolant level. In other words I have one third the cooling potential of a properly functioning system.
But the climate here is not too hot so it's been okay for the few years of ownership.

I did try putting a 13mm box wrench on the bolt and tapping it many many times with a big brass bolt, I will also try the suggestion of heating the bolt gently while shielding the rad.

Cost is an issue, the only way my family afforded this beast was by squandering a small inheritance to pay for it. Luckily I can do all the repairs and maintenance myself, so far.

Before this the most expensive vehicle we ever bought was $3500.

I be very skeptical of using heat. you heat that bolt, well the brass insert will also heat, and that in turn is secured in the plastic radiator side tank, then you try to turn the bolt, and you may end up tearing out the brass insert. Then it is game over for that radiator.

Use penatrating oil, if that fails try to drill out the bolt. Drill it to just avoid touching the threads, then use a tap to clean out any remaining bits of the bolt threads from the brass insert. This is the safest bet if penatrating oils dont work

for rusted in bolts, one usually needs high heat, but that will not work with the plastic. That brass insert is very likely held from turning in the plastic by delicate splines which have dug into the plastic, get that insert hot, and then try to turn the bolt and the splines in the plastic will rip away, and you will be stuck with a leak or spinning insert.
I reckon the temperature needed to break free that bolt from the insert does far exceed the temperature that the insert to plastic interface can accept without failure.

[/quote]

Tue Jul 01, 2025 1:40 pm

radiators and heater cores are 'thermal precipitators'. meaning, hot solution with dissolved solids enters them, gets cooled and whereby SOME of the dissolved solids drop out of solution due to their reduced solubility in colder fluids. combine that with a reduced flow rate due to the greater area of the coolant tubes vs coolant hose, further exacerbating drop out, and you can see why a radiator is "half full" of schmoo after 40 years. it's a sewage settling pond.

a new radiator is good for engine longevity. half plugged is fine for runs to the local State Park. when you're loaded for a trip, pulling up the 7 mile 5% grade, you gonna want a clean, happy radiator.

as the chemist saying goes... "If you're not part of the solution, you're part of the precipitate."

Tue Jul 01, 2025 2:32 pm

1988M5 wrote: This AI stuff is getting annoying. Moderators, this will become a more prevenient issue going forward. One of you guys must be a tech nerd, fix it.

BK

How does AI set up an account in 2012?

Tue Jul 01, 2025 2:34 pm

SCM wrote: 1988M5 wrote: This AI stuff is getting annoying. Moderators, this will become a more prevenient issue going forward. One of you guys must be a tech nerd, fix it.

BK

How does AI set up an account in 2012?
That’s called “playing the long game”…

:wink:

- Dave

Tue Jul 01, 2025 4:58 pm

Van den Broke wrote: Thanks for all the suggestions.

The drilling idea got me thinking - I could drill a small hole in the bolt and thread it for, say, a 3mm (stainless!) screw to bleed it.
If I were really lucky I could loosen the radiator and tip it forwards at the top so I could do the job without having to remove it.

When the van is warmed up the radiator is only hot on the lower third, which seems to indicate that's the coolant level. In other words I have one third the cooling potential of a properly functioning system.
But the climate here is not too hot so it's been okay for the few years of ownership.

I did try putting a 13mm box wrench on the bolt and tapping it many many times with a big brass bolt, I will also try the suggestion of heating the bolt gently while shielding the rad.

Cost is an issue, the only way my family afforded this beast was by squandering a small inheritance to pay for it. Luckily I can do all the repairs and maintenance myself, so far.

Before this the most expensive vehicle we ever bought was $3500.

For better access to the bolt you just grind off some of the metal above it (oh sacrilege!) To bleed it just run it til hot then park it with rear end raised.Any air will collect in the expansion tank. Fill it full and overflow to max. You don't have to deal with the rad bleed screw.

Call Malahat auto for a used rad on the lot or put you on a waiting list. You might get lucky with a fairly new wreck just in. Be aware that "anything vanagon will be expensive" they once told me.

Tue Jul 01, 2025 5:10 pm

I heated a box end wrench with the propane torch to indirectly apply heat to the hex head but this didn't free it up. I agree that heating is not really practical in this case.

I really like Wesitarz' idea.

I had no idea Malahat Wrecking still had VWs. I remember walking around there decades ago when there was a sea of Beetles, pretty neat (or sad).

Tue Jul 01, 2025 5:13 pm

When I snapped the Nissens plastic screw/bolt I put some JB Marine weld on it then ground it down,cut a slot in the plastic screw/bolt with a dremel and unscrewed it later when I had a replacement bolt.

I replaced the original rad when the bleed screw just spun in place which may be the case here.

Tue Jul 01, 2025 6:22 pm

wesitarz wrote: Van den Broke wrote: Thanks for all the suggestions.

The drilling idea got me thinking - I could drill a small hole in the bolt and thread it for, say, a 3mm (stainless!) screw to bleed it.
If I were really lucky I could loosen the radiator and tip it forwards at the top so I could do the job without having to remove it.

When the van is warmed up the radiator is only hot on the lower third, which seems to indicate that's the coolant level. In other words I have one third the cooling potential of a properly functioning system.
But the climate here is not too hot so it's been okay for the few years of ownership.

I did try putting a 13mm box wrench on the bolt and tapping it many many times with a big brass bolt, I will also try the suggestion of heating the bolt gently while shielding the rad.

Cost is an issue, the only way my family afforded this beast was by squandering a small inheritance to pay for it. Luckily I can do all the repairs and maintenance myself, so far.

Before this the most expensive vehicle we ever bought was $3500.

For better access to the bolt you just grind off some of the metal above it (oh sacrilege!) To bleed it just run it til hot then park it with rear end raised.Any air will collect in the expansion tank. Fill it full and overflow to max. You don't have to deal with the rad bleed screw.

Call Malahat auto for a used rad on the lot or put you on a waiting list. You might get lucky with a fairly new wreck just in. Be aware that "
anything vanagon will be expensive" they once told me.

I dont think is practical to raise the rear of van high enough to remove air from the radiator, short of near standing the van on its nose, I dont see how trapped air can be removed from it

The radiator hoses are near the bottom of the radiator You will need to make the hose the high point of the radiator

Tue Jul 01, 2025 7:09 pm

If the hoses from engine to radiator are connected properly, (hot from engine into bottom of radiator...) then air does not get trapped in the radiator.

It is normal for the bottom of the radiator to be hotter than the top because the coolant flows from the engine to the bottom of the radiator, to top of radiator, back to the water pump.

If you run the engine at high rpm so the flow from the water pump is sufficient to pull any air with it from the top of the radiator, the air all bleeds out to the pressure tank.

Tue Jul 01, 2025 7:46 pm

The bottom of the rad was hot, and the top two thirds was about ambient air temperature. Could this still be normal operation (vs. an air pocket), in that the radiator cools that well in the bottom third under light loads?

Tue Jul 01, 2025 9:24 pm

Thanks for the explanation. I never understood where all the stuff came from that makes an old radiator so heavy.

DanHoug wrote: radiators and heater cores are 'thermal precipitators'. meaning, hot solution with dissolved solids enters them, gets cooled and whereby SOME of the dissolved solids drop out of solution due to their reduced solubility in colder fluids. combine that with a reduced flow rate due to the greater area of the coolant tubes vs coolant hose, further exacerbating drop out, and you can see why a radiator is "half full" of schmoo after 40 years. it's a sewage settling pond.

as the chemist saying goes... "If you're not part of the solution, you're part of the precipitate."

Tue Jul 01, 2025 9:40 pm

Excerpt from link below...

"Vanagon cooling systems are a bit peculiar because the engine is in the back and the radiator is up front. The pipes that run between the two are BELOW both, so if air gets into the system it ends up in the highest point, which is the radiator. If air gets in the radiator it will stay there. There is a bleeder screw on the top of the radiator next to the right headlight used to get the air out. But if air gets back in, it will end up accumulating in the radiator again. "

link...
https://gowesty.com/blogs/article-library/cooling-system-in-vanagons-explained

The radiator is a cross flow type, with both inlet and outlet near bottom, flow is from side to side, trapped air will be in the upper cross flow passages. Air floats over coolant, if air gets into the radiator, it is trapped, thus the bleeder screw is needed to remove trapped air. The water pump cannot suck that trapped air out. Trapped air will remain on the top, unless the bleed screw is used to vent it.

If the air could be pulled out by the pump, then there would be no need for the bleed screw, no need for the factory bleed procedure that uses that screw.

TRAPPED AIR WILL REMAIN TRAPPED UNTIL VENTED FROM THE BLEED SCREW.

Wed Jul 02, 2025 6:24 am

I believe that at high rpms, the water pump can push/pull air out of the top of the radiator, but I have neither the time nor the inclination to prove that to anyone. That's not the only thing that GoWesty gets wrong in their articles.

Even though it is possible not to fall off the edge of a balcony even if there isn't a railing, it drastically reduces the risk of falling if there IS a railing. In a similar manner, it is certainly much riskier to run the engine without bleeding the air out of the radiator when filling the system because running the engine with insufficient rpms for the water pump to have the force to remove air from the radiator could easily result in overheating and potential damage. Removing that risk is wise and plenty of reason for the bleed screw at the top of the radiator and for following a good bleeding procedure when filling the system.

Wed Jul 02, 2025 7:37 am

I have 100% seen the Vanistan heater mod move air bubbles from the top of the radiator. After that air bypass I never had a problem bleeding the coolant system again.

Wed Jul 02, 2025 9:51 am

Interesting discussion, I like theoretical as well as experimental approaches to repair issues.

I think if the coolant level in the expansion tank continues to go down for a while with no external (or internal, hopefully) leaks, I can conclude that the air is gradually moving from the radiator to the expansion tank.

Wed Jul 02, 2025 10:11 am

Without the Vanistan heater mod I've never had any issues bleeding the system either 'by the book' or with a bong.

If anyone wants to prove for themselves definitively whether or not the water pump has the force to pull air from the top of the radiator, then I imagine the following procedure should do it.

1. Start with a vehicle that has had the coolant system properly bled to ensure that there is not any air in the radiator. This can be easily accomplished (provided your radiator bleed screw is not seized...) by getting the van up to temp, parking on an incline so the right front is high, crack open the bleed screw on the radiator and allow any air to hiss out from the pressure of the cooling system and make sure coolant starts to weep out around the bolt threads. Tighten bleeder and allow the vehicle to cool down to ambient.

2. With the engine cold, open the pressure tank and remove a cup or so of coolant. Save the coolant for later.

3. With a helper watching the pressure tank, open the radiator bleed screw some and have the helper tell you when the pressure tank level has risen back to full. At that point, close the radiator bleed screw and replace pressure tank cap. What you have done at this point is allowed a volume of air into the top of the radiator similar to the volume of coolant that you removed in step 2.

4. Start the engine and let it warm up to normal operating temperature so the thermostat is open.

5. Rev the engine to 4,000 rpms in neutral and hold it there for a minute or two.

6. Go to the pressure tank and see if the level has dropped. If it has, then the reason why is because the air you introduced to the radiator in step 3 has been purged to the expansion tank and you have proven that the water pump has the force to purge air from the top of the radiator.

7. Next, either wait for the engine to cool to ambient and add the coolant that was removed in step 2 back to the pressure tank or add that coolant to the burp tank. Through consequent heat cycles any air remaining in the system will purge from the pressure tank to the burp tank when the engine is hot, and coolant will be pulled from the burp tank back to the pressure tank and refill it when the engine is cools. Check the level in the burp tank with each heat cycle until it does not drop. Top off as necessary.

Sat Aug 16, 2025 7:47 pm

Okay, so I took the radiator out and drilled and tapped for a small bleeder screw.

First I center punched to locate the hole accurately in the center of the existing M8 hex head screw:

Drilled it 3/32 then tapped 4-40:

Chamfered hole, filed surface flat (not shown):

Here's a few SS 4-40 machine screws for trying, with a nylon sealing washer:

And here it is all back together:

It worked just fine, I oriented the van nose down and topped up the coolant reservoirs. Then I removed the screw and listened to the slight hissing of the air coming out, and then quickly put the screw in.

Over the next couple days I bled the system when it was hot by just loosening the screw a little as there wasn't much air to come out.

When the engine got hot, the whole radiator got hot! Success!

Sat Aug 16, 2025 7:56 pm

Although I think that is extra work to put into what is probably an already used up radiator, that looks like a solid modification that will allow bleeding and probably will be without issue. Good job.