Coolant Boiling

[aspekt9]

Fresh rebuilt engine, I just started it up today for the first time. It reached operating temperature and then it started to boil water out the coolant overflow bottle. I let it cool down, replaced the radiator cap, let it warm up and it didn't leak so I took it out to break it in, got about 6 miles and it started slowly over heating so I pulled over and sure enough it was boiling out the overflow again. I put in a brand new thermostat so I don't think it's that, the radiator cap I tried two new ones (13psi), the lower hose is warm to the touch, the upper hose seems to be filled with air, it's hard and hot. It seems like I'm left with two options, water pump or headgasket. I used an OEM MLS head gasket with copper spray, both the head and the block were machined for an MLS from a reputable shop. I don't smoke out the exhaust, oil does not look milky. Where do I go from here?

 

[wranglerunner22]

First thing is you HAVE to get all the hair bubbles out.

What does your radiator look like?

I know after my engine build and my radiator sitting around the garage it looked kind of beat up, I tried using it and I also had a overheating problem. I bought a Koya and bam problem solved! I dout it would be your HG if you just built it. Did you retorque the head bolts?

 

[jerzeeog]

I had the same issue with my 420A a couple of years back. By the time I changed the water pump the damage was done and I needed a new head. Given that you are sure the head work was good I would suggest replacing with the water pump.

Keep us posted

 

[aspekt9]

So a couple things, I found that my intake pipe pinched the lower hose a little bit. Also, I just poured the coolant in I didn't run the heat full blast to clear any air out of the heater core. I'm guessing this is probably my issue, air in the system. Would air in the system also cause the engine to heat up faster than usual?

 

[firefighter]

It sounds like your air bound.Go to the thermostat housing open it up,remove tstat fill the block with 50/50 mix seal everything back up.Get a good thermomator and measure water temp. at radiator cap opening.run the engine check the condition of the thermastat fan relays etc..While your at it take a pot of water place your tstat in the pot start to heat the water measure the temp of the water.If your tstat is rated for 185 degrees it should open at that temp. When it does read your thermomator. This way you are sure that everything is working correctly.I have seen bad tstat out of the box. hope this helps