Coolant ratio
 

When I filled my radiator up on initial startup I put two gallons of concentrated antifreeze in and about a gallon and a half or so of distilled water. Not an exact measurement but it has a good bit more antifreeze in it than distilled water. My car has a 180 thermostat and it’s running between 195 and 205 at idle and settling down to 195 or so around cruise. I know this is more than acceptable especially in 100 degree South Carolina but I just wondered if it’s the ratio or the thermostat that might be contributing to this. I have a know good 180 I may swap in next year or if this one creeps up. Just don’t want a stuck thermostat to mess me up. Things are running too good.

And just what in your way of thinking does the mixture ratio have to do with having a potential stuck thermostat like you posted about?

Have you driven the car yet at near full throttle and above 4500 rpm for a good lenght of time to see what your cooling system can truly handle in terms of the motors state of tune and heat output?

That's what I would be concerned about, otherwise I don't see a issue with what you posted about temperature wise.

I don’t mean stuck I mean off on it’s reading. I guess after all I’ve been thru I’m afraid if it’s 15 degrees off it’s only gonna get worse. If a bad antifreeze ratio could be the culprit then easy enough. If the thermostat is off 15/20 degrees then I’d swap it for my known good one. When you’ve been down the road I’ve been you take no chances

No 4500 prolonged blasts. No need. 75 MPH is 1550 RPM in overdrive. I have the rev limiter set at 4800 anyway

As I’ve mentioned before, if the thermostat in the engine wasn’t tested it’s possible it doesn’t fully open until 190-195 as some aren’t that accurate. Easy enough to tell when it opens by letting the car idle to full warm up and wait till the upper radiator hose heats up and you can feel it get hot and fill with liquid. That’ll put you in the ballpark of when it starts to open. All that being said your temp is fine especially at that ambient temperature with AC on, as long as it doesn’t keep climbing uncontrollably.

If you are running a mixture of 66% coolant and 33% water, that is fine but the concentration is a little high on antifreeze. Actually, that mix will give you maximum freeze protection of -52 to -55F. That's far more than you need in SC, I would think. On the flip side, the 60% concentration does hurt the coolants ability to remove heat vs a 50-50 mix slightly. Engine may run 3-5degrees F warmer with that highly concentrated mix. Still nothing to worry about. As far as the thermostat is concerned, they are pretty reliable and work as designed IF they are a QUALITY part and not made in China. They generally fail open or closed, not somewhere in the middle . Your running temps sound perfectly fine to me. Have some fun with your car.

Blow this up and print it off to keep in your files .

That’s a great chart - assume the 160 starts to open 157-163 and fully open at 182

Lower the concentration of anti freeze, no need for anything more than 50/50. Water cools better than anti freeze so go to at least 50/50 & consider adding some water wetter or the more easy to find rislone hyper-cool.

I always mix 50/50 when I lived in Ohio, and left it the same living in Arizona. Works fine.

Yes the 160 stats that I've tested start opening around ~155 degrees.

Antifreeze also raises the boiling point of water. Pure water has a boiling point of two hundred twelve. If the mixture is 50/50 water and ethylene glycol, then the boiling point will go to two hundred twenty-three degrees.

Check your temps at idle in traffic and also at highway speed and compare. If the temp remains the same, you're within the limits of your cooling system capacity. You can try a lower temp thermostat and see if it will make any difference but the BTU cooling capacity of the system is probably the over-riding factor. Also make sure you are running a high flow thermostat which has larger "windows" and less restriction.

True, but let's not forget the boiling point of either combo goes way up when under pressure in the cooling system.

I wouldn't call that more than acceptable. Is it okay? Usually. It depends on your scenario. If it's not giving you fits on pump gas with hard starts and heat soak, then run with it. If that's the worst it gets and you have AC blasting cold, then I'd be okay with it.
If that's no AC, or it's giving you fits with heat soak, you'll have to investigate further. Need more information to give honest feedback.

Technically with your 180 stat, if the cooling system is up to par, and the engine is happy (ie: compression/cam/tune), then it should be running very near your thermostat rating. The fact it's hitting 205 tells me the cooling system is running away a bit for one reason or another.

Well now today it’s right at 90 outside. Going down the road and sitting still it’s at 195. Rock steady with AC blasting.

I could live with that with the AC blasting.

Typically mine never gets above 190 when it's over 100 outside and AC going so not too much difference from yours there. Without the AC and temps over 100 it runs 175-ish, so that gives an idea of the difference with and without AC. That's an A-body with 460 cubes and 600hp.

Personally, I am not comfortable running my classic Pontiac that hot, although it doesn't seem to be a problem for most. If you want it to run cooler then get a Cold Case radiator and leave the factory shroud and clutch fan in place. If the water temp goes much above thermostat rating then your colling system is not keeping up.

Steady is the key word. You don't have a problem in my view. Cools down some when you turn the a/c off I assume?

195 too hot? I don't think so. Especially with the A/C on. He is fine. Did you know that some of the 70,s Pontiacs came with a 195 thermostat?

Precisely. I operated my ‘72 GP in S. OH/N. KY/ S. IN summer weather; never had it overheat, even in Cincy I-75 construction traffic on 90+F days. If you know anything about Ohio Valley/Miami Valley summers you know they can be nearly as hot and as humid as SC.

I have the cold case. I think my thermostat is opening late. It’s supposed to be a 180 but as long as it doesn’t go over 205 I won’t switch to my know “good” one.