In my part of the country you can only buy gas with 10 percent alcohol. The BMW dealer tells me the cheaper brands have been as high as 30 percent even though it's not supposed to. There are tons of problems with alcohol in the fuel but vapor lock in the summer in the southwest is high on the list.

 

Seeking advice on cooling problem -

1978 302 V8, stock: I replaced the thermostat with a 192F model, a Stant Superstat to be exact, but my coolant temperature fluctuates. The engine warms up normally, but the temperature gauge tends to sit at one two points. One is slightly below the halfway point of the gauge, and the other is just above. This seems to be pretty random, but sometimes the temperature goes from one spot to the other. These are slow fluctuations.

The engine is certainly not overheating, since my radiator cap doesn't hold pressure (I can open it when the engine is hot, and there is no hiss), and I keep it full. I occasionally have to add more coolant, but have yet to find the source of the leak. Perhaps a head gasket problem?

Should I be concerned about damaging my heads due to air pockets? I don't think the 302 has any place for air pockets to sit in the heads, since the coolant ports lead at an upward angle toward the intake manifold - any air should bubble up into the radiator when the thermostat opens.

I'm planning to do a coolant flush with Valvoline's Zerex product; perhaps this will clean some of the gunk out of the engine. The radiator is new, but the engine likely has a lot of grime in it. When I replaced the thermostat, the inside of the manifold was pretty orange from rust, as was the radiator.

 

the coolant leak may be nothing more than your radiator cap not holding rated pressure. from what you describe about your temp gauge, that doesn't sound really bad. find a shop that can pressure test your cooling system, that wont take long and they may not even charge you for that. flush the cooling system, replace the radiator cap. then let us know

 

Thanks so much. I'm not really concerned about boilover protection since I've never had a problem with REAL overheating, so I might just modify the radiator cap to stay open and install a little coolant reservoir to hold extra.

 

A cap does not cost that much. I just solved a problem I had. The outside temp was 5 degrees. My damn Vic would not warm up. It froze my ass off for over 350 miles. The culprit, a damn 8 dollar cap along with a stuck open 10 dollar thermostat. Both reared their ugly heads at the same time so it was a little confusion to figure out which one caused the no warm up. I would say both. The cap actually raises the boiling point of the coolant (heat) and the thermostat regulates the coolant temp (cool), so my guess would be both. You need to fix this problem. An overheat in the middle of nowhere would be a bitch, even though you said you have never had this problem. Also, you need a coolant catch set up the right way. When the coolant passes the cap, it goes to the jug, when the coolant cools, it draws from the jug if the radiator is underfilled. If I remember right, on hot, your coolant should be one to one half inch under the neck, then cap sealed with a 15 to 16 pound cap. Coolant jug filled between the cold and hot line. Then cycle the hot/cold and see it a draw occurs from the jug. It should draw the jug down when cold.