2000 Grand AM water vs coolant


Asked by Jul 04, 2016 at 07:41 PM about the 2000 Pontiac Grand Am GT

Question type: Maintenance & Repair

Ok guys I'm sorry but this could be a long post as I feel you need to know everything I've done to maybe give an informed answer.

I have the above car. When I bought it, It would over heat on me all the time. I replaced the water pump thermostat and hoses, still overheating. So I did research on it and it turns out that I needed to burp the cooling system. Now I didn't have the money to put coolant in so I ran water and everything was great it ran (depending on how I drove it) from 180 deg to 195 deg. Next payday I bought 2 gallons of 50/50 antifreeze (green) and it ran at 210 deg to 230 deg (again depending on how I drove it). Thinking I ran the wrong coolant I bought 2 gallons of 50/50 extended life (orange) and it ran the same as the green.
I took the car to GM to have the ignition recall fixed (only made a key for me) and asked the tech why the car ran cooler on water than coolant. He explained the difference between running water and coolant but that didn't answer my question.

He said if you run water it will rust the engine unless you run distilled water. Then he told me running straight coolant the car would never reach operating temperature. Thinking like that I drained 1 gallon from the system and replaced it with straight concentrate antifreeze.

So here is my question, if it has mostly antifreeze (which is suppose to make run way below 195 never reaching operating temperature) why does it run at a constant 230 no matter how I drive it, and can someone explain why it runs cooler on water.

I appreciate your feedback


2 Answers


I believe the optimal mix is 50/50 water/coolant. The water dilutes the antifreeze so it flows better through the radiator and water is a better 'coolant,' but antifreeze has properties needed that water alone can't provide - it is a rust inhibitor, and it doesn't freeze and has a much higher boiling point. Too much water, and it has the potential to boil away, lowering coolant levels, and causing the engine to overheat. Too little water, and the coolant mix is thicker and doesn't achieve as low an operating temperature. However that is not really an issue, so long as the engine stays withing operating ranges. With water alone, you also have the potential to never achieve optimal operating temperature, especially if you live in a cold/cool environment. I won't mention what a bad idea it is to just have water in the radiator if you live in a cold area as I think everyone knows about that. Your owner's manual will list the optimal temp for your engine.


It has to do with heat exchange. Some liquids absorb and release heat at different rates. Much like aluminum cools down much faster than cast iron. In the old days, 1950s and earlier, you ran straight water during the warmer months and straight antifreeze, usually alcohol based, in the colder months. Back in those days the typical cooling system ran at about 6 or 8 PSI (Pounds per Square Inch) of pressure and the thermostat, if used, was 160°F. These were low compression, low performance engines. During the '60s when horsepower and engine sises increased "permanent" antifreeze came into use. This was a huge improvement because instead of having to flush out the cooling system twice per year it was now done every two years or 24,000 miles. Whichever came first. In addition the new antifreeze, at the time, was designed to work in the higher, 180°F or 190°F engines. My '66 Cadillac, for example, called for a 180°F thermostat. It was made before emissions standards came into effect in 1968. When that happened car manufacturers switched to 190°F for faster warm up times and lower tailpipe emissions. Operating pressures on cooling systems also increased to 16 PSI to raise the boiling point of the coolant to 260°F with freeze protection to -20°F. This equates to about a 60/40 mixture of water and antifreeze. Later on the concentrate was changed to 50/50 to increase boil over protection and freeze protection to -50°F (I believe). My guess is that you need to bleed the air out of the cooling system using a vacuum/purge tool. If that doesn't seem to work, check for a blown head gasket. With a 195°F thermostat you should be running between 195°F and maybe 210°F maximum if you're stuck in traffic on a hot day with the air conditioning on. HTH. -Jim

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