Not usually...

Here's the thing - when you have a blown headgasket, the compression usually forces it's way back into the cooling system on the power stroke. Hence why you will get bubbles in your radiator, or on some cars, blow up the coolent tank... The cooling system is under pressure when hot and on the intake stroke, the engine sucks the water into the chamber (it's also under pressure)... Basically, you have a vent in one or more cylinders, so most definitely you should see it on your compression gauge...

Given the symptoms that you've described, I would have expected that you would be losing LOTS of coolent. Your engine should still run with one dead cylinder... It will just shake quite a bit but it should still run... You should also be able to tell which hole it is by looking at the spark plug - it should be very clean... The water dissolves the carbon and cleans it out. Also depending on the size of the leak, the plug may be wet... Should definitely be wet if that cylinder isn't firing...

The way you have described the problem, it won't stay running under 2000 rpm... This is why it makes no sense to me... I suppose that you could have blown the gasket on multiple cylinders at once, but then I would fully expect low compression on at least one hole... This is one of the reasons that I felt it might have been a timing issue...

Now I'm puzzled...

Sorry that you went to the work to find it wasn't the timing belt... I would have bet money on it based on the symptoms that you described...

Is this thing using water? Does the white smoke smell sweet? You will definitely know if it does, it isn't subtle...

You can also get lots of smoke from excess fuel in one or more cylinders. That's why I was asking what it smelled like... If it's sweet, then it's coolent. If it's acrid or makes your eyes water then I'd bet it's excess fuel or bad ignition/timing...

Finally, your local tool truck, auto parts or Sears should have a device that you can attach in place or your radiator cap that will tell you if you have a blown headgasket...

Keep us posted.

Steve