Antifreeze and normal operating temperature

2005 Chevy Impala with 3.8. I had noticed my temperature gauge climb quite high and the warning light came on of course. I did the usual check antifreeze reservoir. It was low tossed some in. It still ran hot. One of the fans weren’t kicking on, new relay. Still ran hot. Thermostat stuck closed, new thermostat then.

Now it is running cooler though not as cool I think it should or perhaps it is normal. It’s just above the middle on the gauge. The part guy at the store recondmended that I stick with O.E. at 195. One of the first things when I first got the car was put in a 180 as it is only driven in the summer and on occasion.

Is it because it is a 195 that is making run just a little warm to me it seems like it. When I had the 180 in it barely got to the middle usually just below it or on cooler days even lower. All I can think of is clogged radiator. No antifreeze in oil, it isn’t milky. Is this just normal or should I try flushing first.

Perhaps I do not understand, but running in the middle seems fine to me, had an error code running too cool on my 03 chevy, The gauge was just under the middle. New thermostat and all was good, thinking it wanted to be at 212 degrees.

You should be using the 195 thermostat, it is what the engine was designed to use. The gauge should stay more or less in the middle, not below the middle. With a 195 t-stat, the engine will typically run 200 to 210 degrees as it was designed to run.


Definitely agree. You really do want the 195 degree thermostat.



This is a typical GM temperature gauge. The red arrow is about where I am running. That isn’t too hot or is the radiator dirty possible. I don’t want it running too warm wouldn’t that be hard on the fluids, like oil prematurely breaking down.

Your gauge is not a precision instrument. Your owner’s manual will undoubtedly say the needle is in the proper range. Change your fluids as per the manual and you won’t have an issue. Running at the proper temperature will reduce emissions and increase fuel economy, compared to running too cool. It will also help eliminate condensation from the oil more quickly.


Running the oil too cool is worse than too hot. You want the oil at 215 f to evaporate the water. This isn’t 1970 oil or 1970 engines.

The engine won’t spew coolant until about 260 degrees f plus so you have a long way to go before that happens. Running a tick over center in traffic is perfect.


Other than agreeing with others on their advice I might suggest that if you are concerned about the temperature go to Harbor Freight and buy an infrared temperature gauge.

I buy very little from HF but did get an infrared gauge a few years ago. It was comparatively cheap and testing showed it is pretty accurate. Just point, click, and you have your temp reading.



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Thank you everyone. It is just this car I find it frustrating more so than a Nissan but I trust it and will run her until she dies. I will keep an eye on the temp gauge but it is reading “normal”.

After an hour and a half drive the temperature seemed okay. Highway speeds the temperature dipped down a little and in the city it went up a little.

Again thank you for all your great advice and sharing your knowledge.

Engine operating temps are far more critical now then they were 30+ years ago. The ECU gets readings from many different sources and adjusts air and fuel mixture accordingly. Engine temp can drastically effect air and fuel mixture. May cause engine to run a little rich (thus worse gas mileage).

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First thing, what did the coolant look like when it first overheated. Did it look cloudy or just a clear orange? Did it turn brown?

If it was anything but a nice clear (transparent) orange, then the corrosion inhibiters had broken down and you were getting oxides in your coolant. That may have contributed to the overheating. Certainly a fan not running was a major contributor if the overheating occurred in traffic.

Changing the thermostat may not have actually solved the problem, assuming that you did not reuse the coolant and had fresh coolant put in. The problem would have been solved by the fresh coolant more than the thermostat.

But replacing the thermostat was a good idea, first because it was the wrong one and second because it is near its life expectancy and would have failed in the near future. So changing it was a good idea even if it wasn’t the actual cause, plus it actually could have been the actual cause.

Temperature gauges have gotten more accurate lately, they used to be notorious for being way off, similar to the analog clocks in the dashboards of older vehicles. The smallest increment on your gauge is about 7.5 degrees. It’s about 15 degree per the next slightly longer increment marks. So if your gauge moved up two smalle increments (one medium increment) when you went from 180 to 195, that is to be expected.

I would strongly recommend against flushing out the cooling system. Just change drain and refill the system with fresh dexcool when ever it is anything but a clear orange.

Can you explain why you strongly recommend not flushing a cooling system?



I don’t trust flush chemicals as I have had bad experiences with them. Always had leaks after using them. Flushing with a garden hose can also introduce minerals that can reduce the effectiveness of the corrosion inhibiters. You will never get them all out. If you don’t absolutely need to flush due to a blockage in the system, then I recommend against it.

The vehicle in question is not overheating now, so I don’t think there is any blockage. If someone has a severely neglected cooling system that has developed blockages, then I would recommend a flush by a competent mechanic using a flush machine, preferably using the recommended antifreeze. That would be a last ditch effort to save the cooling system. I would still recommend NOT doing a driveway flush.

Flush chemicals aren’t used unless there’s a serious corrosion/sludge problem with cooling system.

Here’s the machine I use.

The flush machine is connected between the upper radiator hose and the radiator so now it’s part of the loop of the cooling system.

The supply tank is filled with a 50/50 mixture of distilled water and the appropriate antifreeze 10% over the cooling system capacity.

The machined is turned on, and the new coolant is pumped into the cooling system while the old coolant fills the recovery tank.

The hose to the recovery tank has a sight glass, which comes in handy when flushing death-cool from GM vehicles.

You can see when the coolant switches from orange to whatever replacement coolant is used.

While this is happening, if there’s any leaks in the cooling system, they will reveal themselves.

100% of the coolant has been changed.

The machine doesn’t over-pressurize the cooling system because if it did, it would blow the pressure cap open.

All this done in 30 minutes or less with no mess to clean up,

So, your concerns over coolant flushes are baseless.


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Chemicals are not necessary when performing a cooling system flush.

We switched to a vacuum exchange system 25 years ago.

How do you keep the thermostat open during the flush?

I would keep an eye on the fluid in the radiator by removing the radiator cap when cool of course, air and dexcool can sludge. I replaced my dexcool with Peak Global, not prone to sludge issues. My temp guage was rock solid, city or highway, so keep an eye on it.

Most times the pressure from the flush machine pushes the thermostat open.

When that doesn’t happen, the engine is started until the coolant temperature opens the thermostat. Then the engine is shut off because the machine can now hold the thermostat open.

Honda’s are notorious for that.


No issues from dexcool that I’m aware of on my 2005 Sierra with 170k miles on it. I’ve changed it once since I bought it with 137k. Actually, I guess I changed it twice, forgot I had to replace the water pump a couple of months ago. I think the dex cool might not have been the issue, rather it was GM’s gaskets with the dex cool that was the issue early on?

It’s the death-cool.

I know people who switched from the green coolant in all makes of vehicles to death-cool.

And air entered the cooling system and wasn’t caught in time, they ended up with this.



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