I know that it is normally recommended that coolant/antifreeze be a 50/50 proper mix, but I tend to use either a 60/40 or 70/30 mix and was told that this might "be too high" a mix for my '92 Bonneville SE with the 3.8 NA engine. I had a nightmarish experience overheating in my 1980 Olds Regency 23 summers ago (my first new car which had no coolant temp gauge, just an "idiot light," and a defective t-stat installed right out of the factory) and have more concerned with cooling systems ever since!

While winters in the NY metro area are only sometimes super cold, summer'* are extremely hot and humid: the Newark area regularly records some of the hottest temps ANYWHERE in the NY, NJ, CT, PA area betyween June and September, and traffic on the Garden State Parkway can crawl at various exits along the 130 mile road leading to various towns along the Jersey Shore with the risk of overheating more of a possibility!

I'm going to flush the system, drop in the 180 t-stat, and change both hoses this weekend but wanted to know what mix is best since a few coolant brands offer the 50/50 already premixed and can save a lot of time when refilling. But still I feel better with a slightly higher mix that doesn't exceed 70/30. Any suggestions or recommendations about what coolant mix might REALLY be best?

Given your description, I'd stick with a 50/50 mix. Water is a better conductor of heat than coolant. The coolant is there to improve the properties of the water, but not take over its job.

NO. After you've flushed the engine, you're going to have leftover water in there no matter how well you drain the cooling system (e.g. in the heater core, and various cavities in the block.) In order to achieve a 50/50 mix (or whatever other percentage you're shooting for), you need to introduce the right amount of 100% coolant _first_, based on the capacity of the system (it'* in your owner'* manual), then top up the rest of the way with the water.

The 50/50 mix bottles are just for topping up systems later on, not for doing the initial fill. Because your engine will have some amount of water in it already (the heater core will be completely full, among other places), adding only a 50/50 mix will never in fact get your mixture up to 50% coolant in total.

P.*. Might be a good idea to get the system and cap pressure-tested, too. Your boiling point will be too low if the system can't hold the correct pressure.

Personally I flush the system twice a year In the winter I run aprox 50/50, and in the warmer months I run 65/35 water/coolant. I'm not sure if I'd want to go any higher with the water or it might not have nearly as much rust protection.

speaking of coolant, i had to crank the heater on today cos the gage went to 140 Celcius (the end of the red zone) it cooled down a few minutes later wheni got to work, so im thinking its time for a coolant flush and new 180 t stat..should i use gunk brand rad flush or am i better just flushing it with the garden hose?