Steam from radiator cap after head gasket replacement

[v7guy]

Ran across a cheap Civic, 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, all the gaskets, new spark plugs, had the head machined to make sure it was level. Replaced the radiator and the cap. 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 10 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, same results, drove for a bit and again, steam gushing from the radiator cap, but no overheating. Oddly enough, not from the reservoir. Swapped radiators figuring maybe my cheapo $40 eBay special wouldn't seal and again, same results.

Anybody got any ideas what else it could be? Did I screw up my first head gasket in over 15 years?

 

[spo0ned]

maybe some oil is still in the coolant system or engine head was previously overheated and it's seriously wry right now.
Any proofs, just supposing. Hope everything is ok)

 

[v7guy]

maybe some oil is still in the coolant system or engine head was previously overheated and it's seriously wry right now.
Any proofs, just supposing. Hope everything is ok)

Replaced the thermostat and the rad cap again but this time with factory parts, also did the radiator hoses, swapped out the head gasket to a factory Honda gasket and used arp head studs. Looked like things were good for a half hour drive through the mountains, get back home and steam gushing from the radiator cap again, but no overheating. Never seen anything like it.

 

[spo0ned]

same thing, mate. Never seen anything

 

[alex98]

Have you ran a pressure test on the coolant system yet?

 

[spo0ned]

Have you ran a pressure test on the coolant system yet?

radiator cap is fine, so there's nothing wrong with the pressure.
need to look somewhere else

 

[v7guy]

Have you ran a pressure test on the coolant system yet?

So two days ago I ran a pressure test on the cooling system. It held 16 lbs. Then I bled off the pressure and started it up and watched the pressure build. It built up to about 17.5-18 lbs - 1.2 bar. Then the fans kicked on and it dropped to 14 lbs/1bar. So it makes sense the cap was steaming given it pops at 1.1 bar. I continued to watch it and over the course of about 30 minutes the max pressure started to drop and the low pressure when the fans were on came down to about 13 lbs/.9 bar and 8lbs/.6ish bar respectively. Went for a drive everything appears fine. I've put about 350 miles on it. I do get the occasional smell of coolant but it seems fewer and father between.
I assume at this point it was air in the system that even after over a half hour with the front jacked up still hadn't bled out of the system. Keeping pressure on it let it work it's way out. It would appear these are picky and cantankerous lil motors.

 

[impactsocket]

Are you sure the head gasket was done right? You should check for a head gasket leak. You can rent a block tester from Autozone for free but you will have to buy the blue testing fluid for $8.

 

[v7guy]

Are you sure the head gasket was done right? You should check for a head gasket leak. You can rent a block tester from Autozone for free but you will have to buy the blue testing fluid for $8.

Yup, head gasket was totally fine after I used the ARP studs and a factory head gasket. Pressure test on the cooling system showed it holding pressure for a half hour with no leak down. Test for combustion gases in the coolant was negative.
As it turned out the coolant smell was a heater core leaking. It was a ton of fun pulling out the dash.
After that, it did the same thing when first filling the cooling system up, radiator cap would steam for a bit after I bled it with the cap off and the front jacked up for a half hour. Then it acted totally normal. No issues. Never overheated, seemingly ran fine until it threw a rod through the block last week.

Swapped the motor out, same thing. First fill up of the cooling system gave me some steam out the cap after bleeding it with the cap off and the front jacked up... for 45 minutes this time. Steam leaked out for about 15 minutes then it acted totally fine. New salvaged motor seems to run well.