Originally Posted by sofakingdom

Head gaskets are almost NEVER responsible for mystery coolant loss, in this type of engine.



Here's what one looks like, with the holes marked. Sorry the photo is so big, I didn't realize that until after I posted it. Copy it and paste it into Paint or something to see the whole thing.

Cyan is the "steam holes" for a 400, which your gasket doesn't have. Red is the dowel pin holes. Yellow is the bolt holes. Light grey is oil drainback from the rocker arms. All others are coolant. The magenta ones are the most important... they cool the hottest bit of casting in the whole engine, which is, the part of the head between the 2 center exhaust ports... that was what I originally posted this photo to explain to somebody.

Now, LOOK AT the various spacings of things in that gasket, and consider the pressures. Coolant is under 15 psi or so; combustion is in the 1200 - 1500 kind of range. THIMK: if that gasket is going to fail, WHERE is it most likely to do so? Would it not be where 2 1500 psi chambers (aka "cylinders") are right next to each other with only a very narrow strip of material separating them?

This is why, when a gasket fails, it ALMOST ALWAYS affects the way the engine runs. They fail between cylinders, the thin places in those cyan rectangles with the steam holes, and VERY RARELY anywhere else.

Put head gasket failure out of your mind.

Bolts are a different matter... on every single one of them, all 17 per side, the threads are exposed to coolant. If the builder used an inappropriate sealer such as RTV on them, or no sealer at all, then they are VIRTUALLY 100% IRONCLAD GUARANTEED to leak. Which is why I suggested pulling every one, one at a time, and putting some thread sealer (my preferred stuff is the "high temp automotive thread sealer with Teflon" from Permatex or Loctite, same company, whichever brand the label says) on their threads and under their head, and re-torqueing them to 60 - 62 ft-lbs. DO NOT use a "clicker" type wrench. Use a beam or dial type. MAKE SURE you measure the torque while the bolts are actually turning, i.e. DO NOT make the mistake of setting them by their "breakaway" torque. ABSOLUTELY NO MORE THAN 65 ft-lbs: if the torque exceeds that while the bolt is moving, back it out, put more sealer on it, re-torque.

I like that valve stem in a rad cap... so simple and basic and cheeeeeeeep, yet perfectly functional. However a leak typically has to be pretty yuuuuuujjjjjjje to be detectable that way.

The intake gasket is a very good suggestion also. Depending on what kind was used, they can easily fail. The cheeeeep paper-ish ones are total crap and are almost certain to fail rapidly. It will be obvious if they have failed, when you pop the intake off.

If it was mine, I'd pull the intake and exh manifolds, and the valve covers; do the bolts; and make sure the intake goes back on PERFECT. I'll be happy to detail how to do that in a separate post when you get to that point.