68 Eldo coolant issues
 

I was driving back from a car show and noticed my temp gauge was running hotter than normal. The needle was about 3/4 of the way towards hot, luckily I was close
to a pond so I pulled off the road, waited till the engine cooled down and added some
water. I put the radiator cap back on but only half way so as to not build up pressure.
Drove home (about 6 miles) and everything seemed fine. After shutting the car off
anti freeze began coming out the overflow hose. Now it does this every time after the
engine warms up. My first thought was a stuck thermostat or a plugged radiator. I
opened the pet cock and everything looks okay there. One person told me it's either
a blown head gasket or a cracked block but the anti freeze isn't getting into the oil.
I'm not too mechanically adept so don't really want to try removing the A.C. pump to
get at the thermostat housing. Any ideas?

Same issue here. Did u ever figure it out? Under 20 miles no problems. But after an hour trip dumped 2 gallons of coolant. Thermostat has been pulled previously

68 Eldo coolant issues
 

I finally changed the thermostat and it was easier than I expected. I didn't
do it myself but there are three or four bolts to remove and the AC pump
lifts up high enough to get at the thermostat. You don't have to disconnect
anything or remove the belts. Also had the sending unit changed. I don't
take it on long trips but seems to have solved the problem for now. I do
have a problem with the gauge, it reads hot all the time even when you first
start it. My car has both a gauge and a light so there are two sending units.
The other one is at the front of the passenger side head and is a dry socket.
I am currently running without that one as I damaged the threads and can't
get it back in.

Already took thermostat out. Looks like my transmission cooler is leaking into coolant. Pulled some coolant out and put into a jar and it separated into three layers. The gunk on the bottom is either from rust or the tabs that gm put in. Coolant in the middle and then an oily layer on top.

One of the first things I had to do was pull the ac compressor. Have had a hard time finding the right one to replace seems like all replacements are only one pulley