I just helped a friend rebuild his B18C boosted 8 psi. We used ARP head studs (all torqued per ARP specs), brand new Honda HG, new pistons, rings, rods, bearings, water pump, etc. and for some reason after revving to about 6k / 8 psi boost a few times, the coolant starts bubbling in the overflow and sometimes starts actually overflowing out the plastic cap!

I know it cannot be a blown HG cos it was brand new oem! Now we did not RETORQUE the headbolts yet and his radiator is over 10 years old (stock 94 civic radiator no leaks but the cap is also original lol).

I am wondering if we need to retorque the bolts already + get a new radiator cap + bleed the system since I did not bleed it after putting it back together...

 

I just had the same thing happening after my rebuild. Mine was the cap. It was shot to crap (no spring). Do that and bleed the system really good. Hopefully that will solve your problem.

 

I hope its the cap or worse case needing to be retorqued. Just thinking how would I retorque the head studs with the motor in the car? Car is a 94 Civic...

 

have a nice day

 

do a leak down test that will tell you if headgasket is the prob

 

^^
Beat me to it..lol

 

Is this thing tuned? if its on an fmu or untuned you could have very easily popped the HG with detonation, either that or the head or block isnt flat

 

Yes he had the head and block checked for flatness and it was good. It is tuned on Hondata S200. The reason it was rebuilt because it spun a bearing (he just wanted to rebuild and boost anyway). Like I said, the only thing not changed on this car is the original radiator and cap lol. I might have him try a cap today and see ... wish us luck since we dont have bookoo's of money lol

 

headgasket.. you have a leak around the water jacket.

 

did you go and retorque all the bolts when you put the head on? or just torque it once though?

cheap fix is radiator cap especially if it been sitting dry

 

Leakdown and compression Test the thing and stop guessing

 

sounds like your leaking compression into the water jackets, pushing the coolant out. Only happens under boost though. Either the head is warped AND HG is now blown, or just the HG is blown. Do a leakdown like everyone else said.

PS: I had a talon tsi years ago that checked out fine on compression test but underboost it pushed coolant after boost. If you drove around normal it was fine. Head was warped

 

AND THE WINNER IS.................. THE GUYS WHO SAID RADIATOR CAP!!!

 

UPDATE : Drove the **** out of it last night and this morning - no more bubbling - this is proof that it can be something really small and that's what you should try first instead listening to people who say its something biiiiiig right away!!!!!!

 

Awesome man. That's what mine was too. We even did a full pull on the dyno with the cap off and radiator overfilled into a funnel just to make sure it wasn't the head lifting. Lol glad it was a simple fix tho

 

Ty bigmike and yep thats all it was and yea the first thing we thought was headlift lol. So glad that was not the case!!