Rebuilt Engine Blows Water Out Of Radiator

when you pulled the heads the first time, did you check the deck surface for flatness before you reinstalled the heads? you may have warped the heads when the engine overheated. it is also possible that you installed the head gaskets wrong as well. als o start checking the little things like the radiator cap and its ability to actually hold pressure.

First things first. Completely fill the cooling system and do a pressure test. You may be able to rent a tester at a local auto parts store. It has an adapter that screws in place of the cap and a hand pump and gauge. Your system should be able to hold 16-18psi without losing any pressure over the course of 5 minutes or so. If it does, you have a leak somewhere. If the leak is external you will soon find water dripping.

Next, if you don't have a compressor, borrow or rent one. Using the screw-in adapter from a compression tester, screw it into each cylinder, one at a time (remove all the plugs) and plug it in to the compressor to pressurize the cylinder. Make sure the transmission is in park or neutral and your hands and other stuff is clear of the fan blades. If you hear air leaking from the carburetor that is air seeping past the intake valves. If you hear air leaking from the valve cover or oil breather that is air seeping past the piston rings. If you have bubbles forming in your radiator, that is air seeping from a crack in the block, head(s) or a defective head gasket.

If everything checks out okay, make sure you simply didn't overfill the radiator. A full top-tank radiator has the coolant level about an inch below the filler neck. If you have it topped off and the thermostat opens, all that heated (and expanded) water will force more out the top. With the cap on the system will simply build pressure and the boiling point will be reduced. Also check that the lower radiator hose is not being sucked shut by the suction of the water pump. Many of these came with a steel spring inserted in them for this purpose. Last, but not least, make sure you have the correct rotation water pump (which you probably do).

Good luck.

Mr. Wertz,
I have a few unasked questions and some thoughts/comments.
Questions:
>What does your temperature gauge read while the radiator is puking?
>Where is the temperature sender plumbed into the engine?
>What temperature rating and kind/brand is the thermostat?
>Do you have a shroud on the fan?
>What kind of fan and how close is it to the radiator?
Thoughts/Comments:
It is not at all unusual for a newly rebuilt engine to run a little, or even considerably hotter than might be expected, due to the added friction of rings seating and tight tolerances/clearances (a good thing in the long run) of bearings, valve guides, etc. finding their "happy medium"/breaking in. The important thing is to keep an eye on the actual temperature to not let it skyrocket to the moon. Many folks I know put an extra box fan, or such, in front of the radiator during cam/engine break-in to help, especially if there is no shroud. A little "boil-over" is not uncommon as long as the temp becomes steady at a normal to a bit above normal range and the puking stops. If the temp starts to go through the roof, shut it down. Let us know how you make out.
HTH,
Gene

Hi,
Barring any incorrect installations of parts, it is not too unusual what you experienced. While it's true a newly assembled engine will be "tighter" therefore generate more heat, it's a possibility, this increase heat combined with trapped air and super heated internal surfaces is causing your puking. Before you tear everything down, remove your temp gauge sending unit and, at least, one other plug in the intake that has access to the water jackets. Fill your radiator slowly. As the level increases, in both the rad and the block, air will be expunged from those openings in the intake, otherwise it is trapped in the block and you don't get the level of fill you need. If after filling the rad and water does not begin to exit, one or both of those intake openings, proceed to add water through them until it does.
The thinking here, is to purge as much air from the block by displacing it with water/coolant. keep in mind, while your are breaking in a cam for example the engine is racing, first 1500, 2000 etc. unless you leave the T/S out, it takes several minutes before the T/S is fully opened and water/coolant is able to fully circulate. By this time there a number of super heated internal surfaces that will vaporize the coolant reaching it.
It is for these reasons, I'm a fan of coolant recovery systems that purge air and replace with coolant after a few engine cooling cycles. We all know coolant absorbs heat and carries it to the radiator, not air.
Good Luck!

Another easy trick to make sure that all the air gets out, is to just drill a small hole in the thermostat on 'top', in the flat part by where it goes in between the intake and housing....

Hi,
Relative to:
"Thanks poppymod for some ideas. I will try and do that next time. Are you saying that when the thermostat opens, the water will not force out the air that has been trapped inside the block?" No, I'm suggesting until the T'S opens, a lot of heat is being created. When the coolant does make it to those "hot spots" the coolant will be vaporize creating the pressure your seeing as it puke's it's guts. Again., this is barring any parts head gaskets, blocked coolant transfer ports, mal-functioning T/S etc. not correctly installed.
What can be happening is, when you pour water into the radiator, to completely fill all of the voids in the block air has to be purged. That T/S is closed until water in the block and heated is touching the T/S , heating the medium that opens the T/S. Until that happens there are many, what's called "hot spots" that will super heat as air is trapped, at or, nearby. This is why I suggested you remove a couple of those intake water jacket plugs, As water/coolant is being added, air withing the block is displaced and being forced out through those openings. When you see water at those openings, replace the plugs. Now, this is not to say "all" of the air is removed. This is what a coolant recovery tank will do after a couple of cycles. Ideally, you want to remove your rad cap and see the coolant level right at the mouth over flow tube to the recovery tank. This will indicate a fully purged system.
This is only my surmise at this point. Your issues, I've experience early on until I figured it out. Someone wisely mentioned drilling a small relief port in the edge of the T/'S as a air escape hatch. Very good idea.