Should I be concerned about this engine?

My brother's mustang has a professionally rebuilt 1967 200 in it. I don't know how long ago it was rebuilt, but I pulled the head on it and there was no ridge in the cylinders and the hone marks were still plainly visible. I bought it under the impression it had minimal mileage. The pistons had 0.040 stamped in them. I pulled the head because when I installed it in the car and cranked it up, some dark spots appeared at the head-to-block seam on the ignition side. I had given the assembled engine a fresh coat of paint so these spots stuck out like sore thumbs and it was clear that something was seeping through the head gasket. Everything looked good so I put on a new fel-pro gasket and torqued the head bolts exactly per the shop manual's instructions.

The engine runs very well, smooth and even and compression is around 205 psi for all cylinders. I've closely monitored for more leakage, and sure enough after running the engine for a while there are some tiny bubbles here and there along the gasket and it looks slightly moist. There are one or two places where it looks like fluid has collected enough to run down the side of the block, but it must be a tiny quantity because it never looks fresh and there is no collected liquid around the oil pan. The oil is clean and smells normal and has no bubbles on the dipstick. I can't tell what fluid is seeping out because the quantity is so tiny.

Also, after idling for longish periods of time, it always smokes when I accelerate. If I idle briefly, I don't see any smoke though, nor do I see smoke when cruising. The engine sat unused out of a car for at least a year, probably a good bit longer (3 years? 5 years?).

I suspect the smoke is the fault of hardened up valve stem seals (hopefully not valve guides; shouldn't be if rebuilt recently!) and don't know what to make of the head seepage. Do you guys have any wisdom or suggestions for dealing with either of these issues?

Thanks a lot!

Your suspicion about Valve stem seals is probably correct. An engine sitting for a while especially will be susceptible to this.

It is also typical for these engines to weep a little coolant along the driver side. Some have the problem, some don't. I don't know if there is an accepted cure for the problem as I've never had it.

If it were mine, I would probably put a tube of aluma-seal in the radiator and call it good.

oh, okay! I never would have guessed that weepage to be a typical problem. I never noticed it on his other engine, but it was usually so covered in filth I probably wouldn't have noticed in the first place. I wonder how/why it happens?

What's aluma-seal? I've heard all kinds of warnings against coolant system sealers. People seem to think they do more harm than good, blocking off radiator passages and otherwise gumming things up. Not the case?

I'll plan on doing the stem seals next time I have a good opportunity. They're so cheap! I love that about the parts for this car/motor

Well, I've used aluma-seal in just about every engine i've owned at some point, and never had cooling system problems (well, after I used the Aluma-seal, anyway).

It's just a cooling system sealer that comes in a little tube and costs like $2.00.

I started using it on recommendation of an old mechanic friend of mine (one of the few good mech's out there) who told me that he uses a tube any time he opens up someones cooling system.

If you poured 10 lbs of it in you radiator, it might cause clogging problems. But in the small quantities you would actually use it doesn't seem to hurt.

I've got 100's of thousands of miles under my belt with the stuff, and I haven't observed any problems YMMV.

Your block was probably not decked when the rebuild was done.

Typically the block castings tend to deform slightly over time on that side. I have had to take as much as .010" off the deck just to get one straight.

The good news is that the seepage is not critical. Usually it's just weeping from the pushrod passages as the oil drains back. My fix for undecked blocks has been to apply a thin smear of RTV around the pushrod passages prior to assembly. Don't put it on the entire deck, though.

It's not pretty, but it won't hurt anything either.

As far as the smoke, I think you have it pegged. Install new seals and you should be ok. Another thing to check, however, is to make sure you have the right size seal. The 11/32" seal for a small block looks the same, but will not keep the oil under control like the proper 5/16" seal required for these valves. Sometimes they get the wrong ones put on.

Hmm, I wonder why the rebuilders wouldn't have decked the block if it was warped beyond spec. Maybe the warpage occured after they rebuilt it or something (?).

That RTV solution sounds good, but I'd rather not pull the head again if all else is well, which it appears to be. I can do the stem seals with it still bolted on, just have to fill the cylinders with nylon cord or something.

I think I'll try aluma seal. When the seepage first happened I though it looked like oil because it was dark, but since then I've thought it's coolant because of the tiny bubbles that show up. My only concern is that, if the coolant passages on that side of the block aren't sealing, some of the coolant may be getting into the oil. If it's the same amount that's coming out externally, that's still nothing to sweat. But I think aluma-seal will probably take care of it altogether. For $2, can't hurt to try!

I want to make sure I'm getting the right stem seals. 5/16" is the outside diameter of the valve stem, right? Is this something I can trust Autozone or Advance with, or would National Parts Depot be a better choice? I need to order some stuff from them anyway...

i dunno that i'd trust Autozone or Advance
maybe Napa or O'Reilly's

check prices with the catalogs, you might find a good deal

I have put two containers of Alumaseal powder in my radiator to date and have observed zero decrease in the coolant weep. I don't understand why. I think the problem might actually have become slightly worse since I installed a 195* thermostat.

I can't tell yet whether any coolant is getting in the oil. I have about 1500 miles on this motor since installing it and when I pull the dipstick the oil feels viscous and smells right but there is usually 1-3 tiny bubbles in it.

Any other suggestions for stopping the weep (short of decking the block)? Anyone think it sounds crucial to do so?

I would just drive it. The aluma seal can take a while to start working, fwiw.

The leak isn't a problem other than it looks a little ugly. I would drive it for a few hundred miles and see what happens.

It's not going to leave you stranded.

All right, I will take your advice. All I'm really concerned about is coolant getting in the oil and thinning out and whatever else it does to engine lubrication. I suppose the leak is slow enough that even if it is mixing with the oil it might not be enough to mess things up. I'll see how it looks on my first oil change, I suppose.

Still runs great!