My concern is with driveway flushes and they are not baseless.
I have seen this in several vehicles that were WAY overdue for coolant change, only one of them was dexcool. I have used dexcool in several of my vehicles and kept it in there long after the 5 years and never saw this.
Become a professional mechanic, and come in contact with many vehicles over many years.
Then youād see how death-cool got its name.
Tester
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As a professional mechanic, you only get the customers story. They usually donāt tell you how long the cooling system has been neglected.
I do recall in the early days of dexcool, there was a lot of this that GM blamed on a defective radiator cap. You donāt hear these stories anymore so I have often suspected that the dexcool formula was changed a little to prevent this.
When GM introduced Dex-cool, GM removed the radiator caps from the radiator.
And then told GM owners that Dex-cool COULD last five years or 150,000 miles.
That gave GM owners the impression that the cooling system was maintenance free.
Well, get air in the cooling system and you end up with Death-cool.
Tester
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Well after 3 hours of driving on a 90 degree day everything so far is good. I did have the coolant replaced last year during a water pump change. They dropped in like 3 gallons which is spec.
I am still curious on the thermostat and how 15 degrees difference on a thermostat would cause such problems. It just means the thermostat gets open earlier unless you think that the fans and radiator is able to maintain the 180 otherwise it would be in operating temperature and the coolant is getting circulated more often with slightly cooler coolant. Isnāt heat the enemy as it can dry out things, cause more wear, etc. Is there very specific to make/model/engine that would make since to run cooler like the 3800. Even running a little richer with the 180 I was still getting over 26MPG for a car that is 16 years old and has 206K and since it isnāt driven in the winter there wasnāt any need to get the coolant hotter to get heat. Just curious, I am keeping in the 195 in but I would like to learn more cause I search for answers and it is all over the place
Just saying your temp differences from highway and city driving indicates to me something needs attention. not tday but something to keep an eye on.
Right. Iām familiar with air in the system and dex cool forming sludge. I always considered the air in the system (for an unspecified length of time) to be the problem rather than the dex cool.
Iām not a professional mechanic. I still think the ādeath coolā issue must be a bit overblown since there are more than a few GM vehicles running around with it in the cooling system with apparently no issues (including my 170k mile truck).
Iām not a dex cool fan or anything. I have no idea why anyone would opt to change out whatever coolant they have in favor of it (in a vehicle that the manufacturer doesnāt spec it, that has a coolant leak, that thereās a chance not all of the old coolant came out, especially). But, I wouldnāt (didnāt) automatically flush the dex out and replace it with something else either.
A long time ago my oldest son bought a near new 96 Camaro RS; and still owns it to this day.
Those first 4-5 years were nothing but cooling system sludge issues along with 3 water pump failures.
At that point I flushed the cooling system, started using the green coolant, and there has not been one issue with sludging or water pump failures since that time.
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I donāt think youāll have any issues running a 15 degree cooler thermostat all summer. In the winter, the 180 thermostat can cause the engine not to hit the higher target temp of 195 when youāre flying down the highway in 30 degree weather.
I have a Buick lesabre with the 3.8. The rubber thermostat gasket developed a tear in it one winter, allowing a little coolant to get past the thermostat before it opened. The check engine light came on, with the code basically saying the engine didnāt reach target temp, or didnāt reach it fast enough, or something to that effect. So the pcm can tell a difference. The only side affect I noticed was that check engine light. However, I didnāt run the car very long with the cel on before I replaced the thermostat and gasket, so I canāt tell you exactly what would happen long term. Lower mpg for certain, but I have no idea how much lower.
I think 96 or late 95 was the first year they used dex. And the worst year for intake manifold leaks. Ah well. Iām not āBob is the coolant guyā or anything. I havenāt had any issues with the stuff myself.
Right now Iāve got prestone (I think) dex cool. It may be the universal stuff with orange dye in it for all I know 
I agree with you completely. Just have to figure out what to do next.
First you have to determine how long you are planning on keeping the car. Then you have to address an apparent leak issue, then you have to address is it time for a coolant change and if so what coolant to go with.
Have dexcool in my 2008 Isuzu Ascender which is a GMC Envoy and if you do the maintenance on time I have seen no issue whatsoever with Dexcool . In fact at 155000 miles I am still on the factory waterpump .
I ran all last summer and the begin of this spring with the 180. I still got over 26 mpg. The only code ever thrown was a misfire in number cause of a bad coil. My first thought was running a few degrees cooler would be easier on the engine but it sounds like it isnāt.
On a side note. I love Buick with 3.8 that first generation 3.8 is almost bullet proof. Easy to work on. I had a 1987 Buick LeSabre, I thought it was so cool that the hood lifted the opposite direction. You had so much access. The harmonic balancer was the last thing that went out before I got rid of the car.
So heat gauge fluctuates between highway and city, lets say a swing of 7.5-10 degrees in either direction. Warmer in city and cooler on open road. What are the possibilities that cause that?
Last thing I changed was the ignition coils and plugs. The plugs were NGK V-Power Spark Plug which are OEM approved. Last May water pump replaced and new fluid was with Prestone All Vehicles cause where I live Dexcool is $2-3 buck more expensive a gallon. I ran it all last summer with no issue. Stored for the winter and took it out in April. My ideas are an air lock, manifold gasket, temp sensor, and thermostatic fan control.
The GM 3800ās are good motors for sure. The trans on my lesabre is a little sketchy. I figure thatās what will go first.
Iām not sure you have an issue with that small temperature swing. I have a digital engine temp readout on that 05 lesabre. Iām going to drive it today and see how much fluctuation in temp Iām getting, highway vs city.
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The thermostat opens at one temp (195?) and the fan comes on when the coolant in the radiator reaches a higher temp, perhaps 205.
When cruising on the highway the radiator is cool and the fan stays off (unless using the AC).
So the engine coolant is at 195 or a bit more.
In the city the radiator doesnāt get as much breeze, so the whole system reaches 205 before the fan kicks in.
Most modern temp gauges have a ādead zoneā where the needle will park at a certain position and not move over a range of normal temperatures.
Thatās so the typical non-techie driver will not be alarmed by the gauge hunting around.
My 1975 Civic and 1981 Accord had āhonestā gauges, and they would rise a bit higher in city driving and move around when the fan cycled.
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UPDATE
The CIE came on and I ran the code and I couldnāt believe it. It was P0171 (Lean on bank 1). I very highly doubt that something like a vacuum leak or the O2 sensor that cause the temperature questions.
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Me 2: I use them to check a lot of temperature questions.