There seems to be some confusion about cooling service here, especially in the above post.
Leave the cooling system sealers for Larry the Cable Guy.
Never use them in an engine which you want to cool sucessfully. Virtually all sealers which actually seal holes coat the entire inside of the cooling system, engine and radiator, with a pliable material. That's what "fills" the holes. The problem is that sealer is also an insulator so...yeah, you might stop the leak but you also decrease the cooling system's effectiveness. Then, if you take some dim bulb's advice that "some is good, so more is better" and attempt to use sealer, again, because the leak didn't stop the first time; you coat the entire system even more the second time. That really decreases cooling action.
If your Corvette's radiator, block, heads or head gaskets leak, don't put "stop-leak" in the system, repair the problem in the proper manner.
As for the car which starts with a puff of white smoke and smells sweet...the chances are very good you have a small head gasket leak or a cracked head. You shut the motor off and a small amount of coolant pools in the combustion chambers. You fire the engine the next time, the coolant gets burned then cylinder pressure keeps the coolant from flowing back into the chamber.
As for the 327/300 and octane...If you live where it's below 3000 ft and you drive the car even halfway hard, use the highest octane pump gas you can find. The problem with the 300 horse engine is that, yes it has only 10.5:1 CR but it also has a camshaft with short duration. The mild cam causes high cylinder pressure and that tends to make the engine more prone to detonation. Gerally, with cast iron heads 9.5 or 9.75:1 is about as high as you can go and still stay out of detonation, if the spark curve is optimal. With 10.5 and a short-duration cam you may even have to use a combination of 91/93-oct gas and slight spark retard to keep the engine out of detonation.
Finally, the unleaded gas and non-hardened valve seat issue....this can be a durability problem heads on engines which get driven in a sporting manner. The best solution is a Red Line Oil product called "Lead Substitute", a sodium-based fuel additive which offers protection against valve seat recession to the same level as did tetraethyl lead when it was in gasoline in the old days. If the engine is never run hard, ie: easy driving and shows, then you don't need to wory with unleaded fuel. If the car driven in a more aggressive manner than that, and you have pre-71 heads with non-hardened seats, you need Lead Substitute.
nothing worked
ad
hnoes