I was planning on removing my head on my stock '78 today, in pursuit of a suspected blown head gasket. I removed the throttle body (don't ask me why) after removing the plugs and rocker cover, and discovered that it was soaking wet on the back of the butterfly. I had previously removed by BCDD , but still had the vacuum line to the EGR system attached. I was able to pour water from the bottom of my throttle body, in the orifices that lead to the now removed BCDD. There was no moisture in the area where the vacuum is applied to the rocker cover. The only source of coolant in the area it appears, is the vacuum line to the EGR system. This line leads to a valve that is temperature controlled, and threaded into a housing that has coolant circulating through it,and when it reaches a certain temp, it has a thermostat built in , and this lets vacuum go to the EGR valve . Has anyone ever had this valve fail in any way as to let coolant be sucked into the throttle body,and then the engine ?

In a move that may be considered wishful thinking, I bypassed this valve by removing the coolant lines from the housing, and looping it back to the source. I really have no concern for the EGR functioning or not. I took a short drive after refilling my over flow tank. This had to be filled after each drive previously, and was still full on return. The drive was admittedly short, but I pushed it hard. The previous symptoms were: loss of coolant without obvious leak, all plugs showing residue that may be from coolant burn, when stop leak was added to running engine, when the thermostat opened , there was a small puff of smoke out the tail pipe that seemed to indicate burning of the oily residue of the stop leak. No, sadly, I did not check compression, but the car runs hard, and does not overheat at all. Just looking for previous experience and want to know if anyone has seen this before ? Sorry for the rambling and thanks for your replies.

I'll take that as a no...

Ok, it gets better. I have battled the overflow tank lid popping off and puking coolant. Thought this was an automatic head gasket. I kept testing other ideas. As it turns out , it only happens when I drive the car before the thermostat opens. I realize the thermostat does not just POP open, but opens slowly as it warms up. However, if I let the thermostat open completely before I drive, I can flog the car like I hate it, no lid pop off, no coolant loss. If I drive before it opens, I can drive like an old lady, and it will happen like clock work. Okay, I'm open to ideas. Thanks.

Pull the stat and test it on your range with a thermometer.Alot and i mean a LOT of T-stats are junkj roight out of the box.

Yeah, I hear that. The funny thing is, there is no overheating at all, ever. I have an aftermarket gauge that actually shows temp, and it's perfect, hovers just barely above 180 deg (the new thermostat rating) no matter what. I'm considering the radiator cap. The old original one was leaking, so I bought a new one. The new one is rated at 14 PSI. Not sure what original should be, but I saw new ones on a Z parts site (don't remember the name) rated at 7 PSI. Seems like my last Z had a single digit number (6 or 7 ) . I wonder if the higher pressure is just too much for the overflow to handle with the increased water flow of driving at a higher RPM while the t-stat is opening ? I may be grasping at straws, but it's worth a shot. I suppose it's also possible the cap is defective outta the box, as you correctly stated , many t-stats are. My head is sore from all the scratching....

Did you replace your radiator cap with a coolant recovery type?

13 psi caps are standard issue.

Doesn't overheat, doesn't leak...and the problem is????

As I said in a previous post, drive before the t-stat opens, recovery tank lid pops off and pukes coolant everywhere. Drive after the t-stat opens, no problem.

Compression test results;

#1 125 PSI

#2 145PSI

#3 150PSI

#4 150PSI

#5 145PSI

#6 147 PSI

Retested #1 after shooting a little 30 weight oil into the cylinder,and second test result was 135PSI So some leakage is happening on the rings. Opinions ? Comments ? Complaints ? Taking all kinds.