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Discussion Starter #1
Ran across a cheap 2002 Civic LX with the D17A1, it needed a head gasket and radiator. I've done at least a dozen on various vehicles over the years. Figured it would be no big deal.
Changed the timing belt, water pump, tensioner with factory parts, all the gaskets (factory gaskets) also used ARP head studs, new spark plugs, had the head machined to make sure it was level, all the exhaust valves were cleaned up since they were slightly leaking. Replaced the radiator and the cap with Honda parts. Fired it up and it started and ran fine. Bled the cooling system with the front jacked up, heater on full blast until the level stayed filled with no bubbles, took about 20 minutes.
Went for a drive and after 20 minutes or so of driving I saw a rather significant amount of steam, turned out it was coming from the radiator cap. It wasn't overheating. I figured bad radiator cap. I've seen it happen. So I got another one along with new hoses and a thermostat, factory parts again since everyone screams to use factory parts. But after another drive through the mountains it starts gushing steam again. I've never seen anything like it.

Any of you more experienced guys got any ideas what it could be?
 

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Could it be you spilled a little coolant in the fins or a lip of the radiator and its taking a bit to warm up and burn off hence the steam you are seeing?

Filler neck could be out of round letting vapor out around the cap?

Cap might not be seated in the full lock position?

Might have missed something when doing the gasket like a crack into a coolant jacket forcing pressure to rise enough to let steam escape?
 

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Discussion Starter #4
Radiator fan comes on.

Radiator is new, actually it's the second radiator. I got an ebay special first and thought maybe it was the problem.

I didn't notice anything in the cylinders obviously amiss. Machine shop said head was good to go. The radiator cap is clearly seated and it's the second one I've tried, parts store brand first and now factory replacement.

Cap is clearly spraying coolant, I dry it off before the test drive and there's light moisture around the neck when I get back.

I'm starting to wonder if the block is cracked, but from my understanding it's essentially unheard of with these lil motors
 

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Discussion Starter #5
Ran a test on the coolant, no combustion gases present in the coolant. No steam out the cap when it's idling cold it warmed up, no steam out the cap when I hold it at 4k rpms for three minutes in neutral. But when I drive it and the engine is under load I get tons of steam coming from the radiator cap. Coolant stays full it appears. No appreciable difference in reservoir coolant level. I'm good and stumped, no idea what else to even check. Any suggestions?
 

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Try another radiator cap. Might have a warped or bad one, even out of the new box.

Make sure the hole that leads to the overfill is not clogged.

Make sure the hose running from radiator to overfill is not damaged. Could have a pin hole near cap.
 

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Discussion Starter #7
This is actually the third radiator cap. One is the original old, 2nd is the new parts store brand, and 3rd is the new factory one. They all do the same thing.
I'll check the reservoir line when I get home from work.
 

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had one of those problems once on another vehicle, exact same syptoms, after taking head off, facing, crack testing, new this new that, flush radiator etc etc and it still blew water and steam out of the cap.
Tested it again with no thermostat, same.

I know previous owner drove it sometime unknowingly over heating etc.
He tried to find the problem....nothing obvious.

By the time we got around to figuring what it was, put another motor in.
same radiator, same cap, same everything, no problem, still have that vehicle, my van.

What else could it be except a hairline crack in one of the cylinders ?
cast iron block btw
 

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Discussion Starter #9
Bought a 2002 Civic but it's giving me a hard time, any thoughts? Solved

It appears even despite jacking up the front and bleeding it for over an hour total, it was likely air in the system.
I hooked up a radiator pressure gauge and it held 15lbs. Then fired up the car and watched the pressure climb, it went up to 16.5 - 17 lbs, when the fans kicked on it would go down to 12ish. Above the cap range at max, hence the steam. I watched it for a half hour without it jacked up and it slowly started to reduce max pressure. Low pressure when the fans were on kept going lower and lower. Drove it around for a couple hours and it all seems good now. I assume steam was forming in air pockets and making its way to the cap and bleeding off since the steam pressure was high.
This D17A motor is a finicky lil monstrosity. Been an interesting puzzle. Hope this helps someone else in the future.
 
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