Engine Runs Cooler with New Prestone - Why ?

[Turk]

Howdy,

I have a '03 GMC Sierra, 5.3l, 106,000 miles on the original DexCool.

A good local shop flushed the system and put in the new Prestome long life. It's a light Yellow. He said the DexCool looked good yet.

Now, I noticed the Temp Gauge does not settle at the same location as it has before - it is off to the Left a bit.

Given the numbered graduations, I'd say it now runs ~ 3-5 Degrees cooler. It is reproduceable over several hot days.

Is this normal? Did it perhaps flush some gunk out that made it run a little hotter before??

Anyone else notice this??

 

[rriddle3]

Pretty normal results compared to coolant with 100,000 miles on it. GM's word or not, I'll still change Dexcool out ~3yrs or 30,000 miles.

 

[unDummy]

Yep, its amazing what a flush can do, especially if shop used a cleaning compound. At 106k, I'd even consider replacing the thermostat. Its been through enough heat cycles and is a maintenance item that is commonly neglected.

 

[Turk]

Interesting - didn't ever think I'd see a difference, but some of my previous vehicles just had the idiot light, so how you'd ever know.....

This truck pulls a 3k Lb boat, hauls wood, but I treat 'er good.

Anyone else notice a lower running temperature when changing coolant??

 

[Lonnie]

Cooling system performance is important and it's the single most common reason for cars in fleet service to break down.

 

[Turk]

Yep, I agree.

But what would cause the engine to "run cooler" with new coolant in it ??

 

[va3ux]

The specific heat of the new mixture must be higher than the old stuff. More water and less glycol cools better than a mixture with high glycol and lower water content. So your old stuff may have been heavier than normal in glycol concentration than what they replaced it with.

But you have to also consider the boiling/freezing points of the mixture when playing around with this. Straight water cools better than any glycol mixture, but it has lousy boiling and freezing characteristics for engine-use.

And, if they did a real good flush at the same time, that may account for some or all of the cooling improvement.

Quote:

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Yep, I agree.

But what would cause the engine to "run cooler" with new coolant in it ??

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[1sttruck]

If they did a flush and filled with 50/50 coolant/water, it's less than 50% coolant because of the water left in the system from the flush.

 

[Al]

Quote:

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The specific heat of the new mixture must be higher than the old stuff. More water and less glycol cools better than a mixture with high glycol and lower water content. So your old stuff may have been heavier than normal in glycol concentration than what they replaced it with.

And, if they did a real good flush at the same time, that may account for some or all of the cooling improvement.

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Actually the cooling medium concentration has almost nothing to do with it. Its true that water can hold more heat per degree of temp but in the steady state operation there will be little, if any difference.

Reason is that every btu that gets removed from the engine must get rejected in the radiator. Initially the engine will cool faster bc the water picks up more heat. But it then rejects less bc it holds more heat (in the radiator). Remember that the water will be at a lower temp at the radiator and thus delta Temp is less in the radiator. (Delta Temp = difference between cooland and ambient air temp)

I agree that it is the flush that makes the difference.

 

[Turk]

That's interesting.

I've been wondering if the DexCool just runs hotter than the new Prestone (??), but that may explain it instead.

 

[99]

I just flushed my cooling system and put in the same type of "yellow/green" Prestone long life pre-mix and my Jeep did the same thing afterwards. It runs about 5 degrees F cooler. It has to be something with the antifreeze as nothing else was touched.

 

[Shannow]

cooler water temperature does not mean cooler metal temperatures (i.e. engine running cooler).

If heat transfer is messed up, the DT between metal and coolant increases.

 

[salvageyardteen]

The flushing probably was the reason.

 

[99]

Nah. My engine and radiator are squeaky clean and were prior to the flush. The only reason I flushed was to get all the "green" stuff out before putting in the "yellow" stuff. Otherwise, I didn't "need" to flush it. The temp decrease is due to the antifreeze. That's my story and I'm sticking to it.

 

[Big Jim]

With all the opinions floating around here I'll toss in another one or two.

I have experienced engines running hotter with too high of a concentration of coolant. I have solved overheating problems by adjusting the concentration back down closer to 50/50. One of the worst I experienced test at over 80% coolant.

Even if you think you have an immaculately clean system, it may have had a little of something on the inner core hurting transfer, so even a drain and refill, let alone a flush, may have helped.

 

[salvageyardteen]

Quote:

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Nah. My engine and radiator are squeaky clean and were prior to the flush. The only reason I flushed was to get all the "green" stuff out before putting in the "yellow" stuff. Otherwise, I didn't "need" to flush it. The temp decrease is due to the antifreeze. That's my story and I'm sticking to it.

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The only squeaky ones are the ones that have never had anything in them. But you go ahead and believe what you want.

 

[wsm41bn]

i used to run the old Green coolant in my dodge m882 and it stayed at 190 all the time and it did heat up on a long grade, so i did a flush and put Global charge coolant(dex clone) in it, ant it stays at 180 no matter what so im happy

 

[Nathan]

You can't trust stock analog gauges. Most only have three settings: cold, operating temp, overheating.

 

[99]

Originally Posted By: salvageyardteen
Quote:
Nah. My engine and radiator are squeaky clean and were prior to the flush. The only reason I flushed was to get all the "green" stuff out before putting in the "yellow" stuff. Otherwise, I didn't "need" to flush it. The temp decrease is due to the antifreeze. That's my story and I'm sticking to it.


The only squeaky ones are the ones that have never had anything in them. But you go ahead and believe what you want.
Well allow me to retort. The radiator mentioned above had the top tank seal fail, so I took a sawzall to it and cut it in pieces and guess what I found? No buildup or anything "foreign" inside of it. It was like brand new. Believe it brother.

 

[99]

Originally Posted By: Nathan
You can't trust stock analog gauges. Most only have three settings: cold, operating temp, overheating.
I'm running a mechanical AutoMeter Ultralite temp gauge in addition to the factory gauge in the dash pod. Both read the same operating temp.