1970 Cadillac Eldorado coolant overflow again

How long since a tune-up by someone who knew what they were doing?

The first thing I would check is the vacuum advance in the distributor. If the advance diaphragm is still good (unlikely if it is original) then check the thermostat. Also check the lower radiator.

-jim

are you sure you don't have any air in the system?

You can always try a new thermostat, or maybe put a lower temp one in.

m6onz5a wrote in news:1b2f6637-eebc-4d40-8f15- snipped-for-privacy@k19g2000yqm.googlegroups.com:

how old is the water pump. some of those old beasts would eat the impellers us so they wouldnt move enough water. KB

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Sounds like you don't have a high enough concentration of antifreeze. Do you have an infrared temp gun you can aim at the thermostat housing to see what temp the coolant is at? The last vehicle I had that did what yours is doing was cured with a new radiator cap but you say you've already put one on it. Are you sure you put on the right pressure rating cap, it probably is supposed to be a 15 pound cap, maybe you put on a lower pressure cap then that. See if there's a gas station that has the gizmo that can check your coolant concentration to see if the ratio of water to antifreeze is at least 50/50.

I seem to remember this topic from a long time ago.. I think we talked about hot spots in the engine, especially when cooling was marginal anyhow. When the engine was shut off, there was still enough heat in these areas to cause local boiling.

Now, what to do about it?

Troubleshoot systematically... Make sure you dont miss anything small... Correct (double check) thermostat? Water pump impeller? Lower hose collapsing leading to overheating? Mineral scale (includes silicates) in the block or radiator? Debris between the air conditioning condenser and the radiator? Air bubble in the engine? Cracked head, block, or blown head gasket?

I will try to search this symptom a little, because I remember it well, but dont necessarily remember the normal cause of it.

xxxx I just now saw this.......I have a warmed up 500 in a 78 Seville.

When you shut down after a good run the stored heat will push coolant into the reservoir tank. If the reservoir is filled beyond the cold fill line it might push some coolant out of the reserve tank overflow which is normal. As the system cools the coolant will flow back into the radiator as the cap has two seals and this allows the system to purge air so if you remove the cap on a cold engine you will see the radiator is filled to the cap. That's when you check the reservoir tank to see it's coolant is at the cold line.

To my estimation this is the finest engine Cadillac ever built.