Useful life of Dex-cool - trouble with a 4.3 S10...

[BraemerZ28]

I have a 2000 GMC Sonoma with the 4.3. Original coolant in it - only 80,000 miles in 8 years. Running a 160 degree stat, AirAid cold air kit, AirAid TB spacer, 2.5" Flowmaster cat back, HPTuners tune for 93 octane, and a B&M trans cooler.

This winter I started having trouble with the thing heating (happened BEFORE the tune). Replaced the stat with a new 160 unit - still no heat. Thought maybe there was a vent door or something under the dash that wasn't opening totally. Replaced all of the vac lines under the hood. Found a lot of cracks. With the new lines, the motor moved from vent to heat to defrost much quicker. Thought maybe I had it. But still no heat.

Winter ended, was thinking about trading the truck so I forgot about it.

Now, truck seems to get warmer than it ever has before. With the 160 stat, the hottest it would ever get even in summer would be 180 or so. Now, in 78 degree weather like this afternoon with the air off, it's running 180. When it was "hot" out two weeks ago (above 90) and I had the air cranking, the thing ran above 220. Unerstand that 220 isn't the end of the world, but with a 160 stat, it seems high.

Question 1:
Does Dex-cool degrade and start to clog/crystalize/something? I thought 10 years or 100k miles was the rule now. Could it be gumming up and causing a loss of flow to the heater core in the winter and now a loss of flow to the rad in the summer?

Question 2:
Would running a 93 octane tune with more timing cause the hotter summer time temps? I've been logging with HPT looking for knock. When I see some, I've been bumping timing down in that area and re-smothing the curves. If it's not knocking, it should be OK. I think. Still wouldn't explain the lack of heat in the winter though.

I plan to have the cooling system flushed in any case to see what happens. Any other thoughts or experience that might suggest what to look for?

Thanks,

[0TransAm0]

did you reset the fans for the 160 stat?
they could not be working properly.
as for no heat im not sure.. did you check the heater core?
i good flush and new coolant first then start checking other stuff.

[BraemerZ28]

Mechanical fans - no resetting possible.

Does the heater knob control coolant flow to the core or just air flow over it? If it control coolant flow, I suppose I can just grab the inlet and outlet lines to see if they're getting hot when they're supposed to.

Hmm...

[GTSLOW]

I replaced the coolant in my 96 S10 in 2003 when swapping over to a 160* tstat. It took a WHILE to get all the crud out. My guess is yours is nasty also. I've talked to a few people and have always heard 5years with dexcool. I think the slightest leak that allows air in will also cause it to head south quick.

btw I said the hell with it and went with the green stuff and had no problems. When I swapped in a Be-cool radiator in 2005 the green stuff looked GREAT.



Just noticed you have an NHRA. I just traded in my 02 NHRA T/A.

[BraemerZ28]

I replaced the coolant in my 96 S10 in 2003 when swapping over to a 160* tstat. It took a WHILE to get all the crud out. My guess is yours is nasty also. I've talked to a few people and have always heard 5years with dexcool. I think the slightest leak that allows air in will also cause it to head south quick.

Just noticed you have an NHRA. I just traded in my 02 NHRA T/A.

Good point of reference. I will try the coolant ASAP.

Yep - 2000 NHRA in the garage with only 17k on it. Really enjoy it. Looking to do a heads/cam swap this fall. Just had my WS6 wheels widened to run 315's while keeping the stock look. Fun toy.

Later!

[Windsors 03 Cobra]

LoL you might as well replace your heater care, radiator, water pump, manifold gaskets along with that coolant, I changed my 00 S10 to green at 40k and avoided all those ugly dexcool problems.
I would not run any coolant longer than 4 years or 40k, rather go 3 years or 30k. I wouldn't run dexcool period and find it ridiculous that GM advertises 5 years 150k change intervals right on most under hood surge tank.
Supposably thats what the consumer wants tho, highly complex maintenance free mechanical machines.

The answer is 5 years or 150k according to GM, is yours mud or still mostly liquid ?

[BraemerZ28]

Overflow tank looks fine and what I can see in the top tank looks OK. When I swapped the stat this winter the stuff that came out also looked OK.

Hopefully it's not too far gone and a good flush will get things moving again.

[Russ Jerome]

btw I said the hell with it and went with the green stuff and had no problems. When I swapped in a Be-cool radiator in 2005 the green stuff looked GREAT.

Dexcool is the kiss of death for GM gaskets while against aluminum.
GO GREEN! No longer a wifes tail do a Google search on Dexcool
and corosion in non ferous alloys.

I bought the first Impalla SS in WI, late 93 (94 model), drove it home
and dumped that crap with 18 miles on the odometer, replaced a water
pump in 100k miles only because I was upgrading the LT1 distributor.

[BraemerZ28]

Thanks for all of the replies. I tore into her today. It was as suspected - the coolant had started to break down. The heater core was TOTALLY clogged - I took the outlet tube off and it was bone dry!
Took the garden hose and held it to the inlet side and a bunch of red slime came out the other end. Ran the water through there until it was clear. Did the same with the overflow tank - clean water and a bit of air pressure to clean that out. Left the drain on the rad open the whole time, took the stat out, and put the hose into the top tank and let that run until it was all clear. With plain water in it now, the heater works like a charm and the ECT's stay right where they should - mid-160's.

I'm going to drive it for an hour or two with the plain water and a bottle of Prestone radiator flush in it and then repeat my flushing process before putting clean green coolant into it.

Thank goodness it cleared itself out and I didn't have to take the heater core out.

Later!

[Car Guy]

DEXCOOL is JUNK and I've been screaming that for years...!!! Pull the T-stat and run a cup of Dawn dish soap through the system letting it get nice and hot, like 200-220. It sounds redneck but it works better than any kind of 'flush' that you can buy in the stores.....

AND WHEN YOU REFILL IT USE THE GREEN STUFF...!!! Another thing I've been doing for years.....

[GTSLOW]

find it ridiculous that GM advertises 5 years 150k change intervals right on most under hood surge tank.

Job security.


To the OP, glad to hear you've found the problem.

[wrath]

You need to change it regularly no matter the kind. 3 years or 50,000 miles, same with ATF, gear oil, and brake fluid.

Modern cars that don't have overflow tanks that vent to the atmosphere will last a lot longer in the coolant department than older ones that do have atmospheric contact. But no matter what you can't do much about all the dissimilar metals, organic compounds, and inorganic compounds in the cooling system.

My Silverado was 8 years old when I sold it with 185,000 miles. It had the original dexcool in it. And it needed a heater core when I sold it.