Open the overflow reservoir, that hose goes down (like a straw) to the bottom of the reservoir. You should be able to blow into that hose & it blows out through a little hole where you put the red circle. Don't go crazy with air pressure. I'd be careful about blowing with your mouth because you really don't want any antifreeze in your mouth.

If needed, pull the hose off the plastic nipple at the radiator neck. Poke in there with a wire or something?

 

I already pulled the overflow tubes and checked them all ... free and clear, ~3/16" ID on these. Plenty of air and fluid flow.

I then connected a short piece of plastic tube directly to the overflow nipple at the radiator neck, and blew. Nothing, and I think the only air I was able to push through the tube escaped at the nipple connection.

I also poked a rod inside there to see if it was clogged with caked on material ... it felt solid to me. This is why I suspected a dropped breather channel inside the plastic ... maybe that's overthinking it

I will take another good look when I get home. If you think there should be a nice 1/8" to 3/16" hole staring at me, then it looks like this radiator has been working for the past 2 years that we've owned the car -- and possibly it's entire life -- without a coolant overflow system! (One of the upper fan housing bolts is missing though, so there may also be an undocumented radiator replacement sometime in the past.)

If/when you get to your Honda, if you wouldn't mind popping the radiator cap and confirm the hole position and size, maybe take a pic, I would appreciate it. I can't find any pics of the Honda radiator online that show this. (All other auto radiators have a nice big hole there.)

Thanks. John

 

I just looked at the 97 SE outside, there is a small hole there. No where near the size of the tube...more like the size of the "straw" you get with a can of carb cleaner.

You ight have to take a paper towel and wipe inside the lip to remove the fluid/coolant in that lip to see it.

 

Yeah, you should have been able to blow air through it without too much effort.
I don't recall it being very difficult to see that hole inside the radiator neck.

 

Well, guess what? No hole.

I took the cap off this morning, wiped the outer ring of the neck dry and looked in and felt around in there ... only a slight dimple, but no hole.

So I started poking a straight pick in through the nipple, and I eventually broke through to the outer ring of the neck, and was able to route it out to maybe 1/16" of an inch.

This was not debris or crud -- I had to break through a thin film of hard black plastic to get through.

So, in the injection molding process of making this radiator top, someone forgot to route the passageway. And the car has been running with a fully pressurized cooling system with no relief valve. That helps to explain the cause of the leaking water pump and exploded top radiator hose which started the whole process of me revamping the cooling system. (I'm glad I did though -- the car really needed a timing belt change and the belt pulleys were actually wobbling).

When I get home again tonight I will clean out the hole a bit more and then go for a test drive. I will probably pick up a new cap and overflow hoses just for good measure as these are looking old.

Thanks for providing the reference info on your radiators ... another future crisis averted!

And I guess this is something that should be noted on the forum ... if your coolant reservoir doesn't seem to be doing anything, make sure the vent tube actually has an opening into the radiator neck.

Thanks. John

 

Hey, it's nice to know the actual end of the story. Thanks for the explanation.
(sometimes we never find out...)

I copied this part over to the DIY forum because I think it's a nice explanation of a strange problem.

 

Update -- I routed out the hole to 1/8".

I used a series of drill bits starting with 1/16", holding the bit and twisting it with my fingers to drill through the plastic. Once the bit was in I moved to the next larger size ... 5/64, 3/32, 7/64, and then 1/8. Each time it was fairly easy to turn the bit and scrape away a bit more plastic from the almost/formed hole. After I had 1/8" cleaned out I tried 9/64", but the bit jammed pretty hard and wouldn't turn ... so the hole must have been molded to 1/8".

I will pick up a new cap from the dealership before I warm the engine ... just in case the main pressure relief wasn't working on the old cap (now that there is actually a place for the pressurized steam and fluid to escape.)

 

Congratulations Jkowtko for finding that weird problem and to all those who helped. I didn't participate but I have enjoyed reading this thread. I bet the cooling system will work fine now, glad it wasn't a head gasket.