By on August 6, 2012



Nate writes:

Ok, you asked for input and I’ve got a question about my 2003 Cadillac CTS. I figure I’m more likely to get a reliable answer from you and the best & brightest of TTAC than the goof balls at Car Talk (this letter is from February-SM), so I’ll ask.

I bought this CTS back in November. It had 135,000 miles on the odo, came from a private owner and apparently had significant engine work accomplished a year or so ago apparently as a result of a timing belt failure after it wasn’t replaced on schedule. Before being able to get the car licensed, I paid to have the thermostat and temp sensor replaced as I had a CEL and a P0128 code and the car wouldn’t pass inspection with a CEL code. The code came back after just about 1 week.

The CEL will clear if the ambient temps move up above 45-50 degrees but returns when the temps get back down to Utah normals for winter. I’ve been unable to find an online solution. I’ve considered installing a temporary partial radiator block, (cardboard & duct tape) to see if that old school fix brings the temp up. The car doesn’t have a temp gauge- thanks for nothing GM; but seems to warm up the cabin appropriately if not exceptionally fast.

Am I going to have to reset the codes each December before taking this in for emissions inspection or is there a real fix?

Sajeev answers:

Much like LSX swaps for people wanting to make a slow car fast, much like Panther Love for someone wanting a cheap and durable ride, I pretty much always think Dex-Cool is the problem when certain vintage GM products have temperature control problems.  As this paragraph shows, Dex-Cool is not my friend…and I am somewhat less goofy than the Car Talk peeps.

On the plus side, others are in your situation and they agree with me. Let’s face it: the timing belt proves that this car was neglected.  It’s a safe bet that Dex-Cool was never changed either, possibly topped off with non Dex-Cool compatible fluid too.  So there is a TON of the stuff you see in the photo below. And above. So I suspect that the 1 week grace period you mentioned was the time necessary to re-clog that temperature sensor and cause the P0128 to trip yet again.

I’d recommend a closer look at your cooling system, probably replacing the radiator too.   Just be careful how aggressively you remove Dex-Cool from the cooling system, you could flush it all out and get a ton of Dex-Cool “snot” stuck in the heater core. Which means you no longer have a heater. Which means…well, have fun removing the interior to get the heater core out. In a Utah winter. Damn, Son…

Sorry, I wish I saw another way out.  Maybe the B&B can help.


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22 Comments on “Piston Slap: Too Cool, or Dex-Cool?...”

  • avatar

    Agree totally with Sajeev. Dex-Cool per se is not that bad – the problem was the manufacturers claims that it could go 100,000 miles or so between changes. Personally, I don’t believe any of these 100,000 mile fluid lives for any fluids – I change all my vehicles fluids at least every 30,000 miles.

    That being said, I would remove the radiator and have a pro shop inspect it. It might be salvageable, might not. Find out where the block coolant drain plugs are (a V-8 usually has two, one on each side), and remove them. Use cleaning chemicals and flush, flush, flush your engine with the heater TURNED OFF. That way no “snot” can get into the heater core. Once gunk stops coming out with the engine flush – THEN turn on the heater, and flush it. With luck, it won’t clog. Or; better, you could locate the two hoses going to the heater core, remove them, and flush the heater directly. At 135,000 miles it’s probably time to change the rubber heater hoses and radiator hoses. Most EFI engines have coolant circulating through the throttle body, so change those hoses and flush out the throttle body coolant passages too.

    Any car with 135,000 miles needs a new thermostat, so replace that while you are working on the cooling system. To really flush the engine, you might want to do it with NO thermostat in place, then put the thermostat in once the coolant passages are clean. Don’t drive the car with no thermostat.

    All this may sound like a lot of work, but it’s the difference between saving a very expensive engine, or allowing it to fail.

    Finally, a simple but not always done check – is the front of the radiator clogged with leaves/bugs/dirt?

    Good luck, and if you get everything in good shape change your coolant at least every 30,000 miles.

    Finally finally – with a neglected car with 135,000 on the clock change the power steering fluid, transmission fluid and filter, oil and filter, and brake fluid.

    • 0 avatar

      On most modern cars, the heater core cannot be “turned off”. Coolant flows through it all the time, the heat knob (or climate control) only adjusts how much air is flowing over the core.

    • 0 avatar

      1. You cannot turn off the heater core.

      2. You do not need chemicals to flush your coolant system. Water works just fine.

      3. You don’t need to completely rip the radiator out or pay some monkey a boatfull of money to check it. You can pull the hoses and flush it in-situ. If it doesn’t leak and isn’t clogged it’s not broke. Radiators are delicate, but stupid-simple.

      4. Thermostat isn’t a bad idea. Cheap and easy to replace.

      3. Ditch the DexCool and use something else. Anything else.

  • avatar

    I think Sajeev is right. If I recall, 2003 wasn’t so good for some GM cars and stuff. 2003 wasn’t so good for me, either, but that’s a different story. Hope you, unlike me, still have two good eyes…

    My old 2004 Impala came with Dex-Cool, but my mechanic swapped it out when I took it to him for its 60 & 90K servicing. Chevy did the 30K service. Each time all fluids were changed, so I never had an issue with Dex-Cool and my car had the 3.4L engine.

    Cooling systems in modern cars are very touchy and must be cared for carefully – along with everything else, but I’m preaching to the choir… In other words, your car’s cooling system wasn’t – the rest of the car didn’t seem to be that well cared for, either, so you have work to do if you plan on keeping it.

    Now would be a good time to not only change the radiator, but might as well dig deep and do the heater core, too, as I’m sure you have plenty of time on your hands – yeah, just kidding, but if you want to keep the car, perhaps it’s the best thing to do, unless you can isolate the core and forward-and-back flush repeatedly to clean the goo out that may be waiting to clog and freeze your backside off when it gets cold and when you least expect it!

    Hope it all works out well for you. I love a Caddy CTS.

    • 0 avatar

      Correction: I think my mechanic kept the Dex-Cool, as when I checked things out under the hood, the coolant was still pinkish, so I believe it was still the same stuff.

      My 2012 has it as well.

  • avatar

    Really? remove the coolant that the engine was designed for an replace it with another? I thought the seals, gaskets, etc were designed for this specific formula.

    I’d like to know since I have a 2006 Impala and made sure they used Dex-Cool when it was changed at 90,000. I’m coming up on 120,000.

    • 0 avatar

      From what I’ve read, there is a lot of controversy over whether a propylene glycol based antifreeze, such and Dex-Cool, can be swapped with an ethylene glycol antifreeze (green coolant). The only thing everyone seems to agree on is to not mix the two – i.e. if you are going to swap your Dex-Cool for green antifreeze, get all the Dex-Cool out first. Also, mix your antifreeze with distilled water instead of tap water. My experience with controversial topics is that there is little difference between either side of the argument.
      If one side was clearly superior, the controversy would end quickly.

  • avatar

    I’ll give my $.02. since I just dealt with this mess on my 2004 Pontiac Grand Prix GT1.

    I had made the mistake of mixing of the traditional green antifreeze with the DexCool. This resulted in producing a thick clay like material in the heater core and radiator. Both were clogged pretty good. Had no heat at all and was having an overheat condition. This is what I did.

    1. Drained Coolant
    2. Back Flushed Heater Core ( Look on YouTube for the process)
    3. Purchased some powdered Cascade Dishwaher detergent
    4. Mix one cup detergent to 2 liters of water.
    5. Fill radiator with solution and top of with water.
    7. Drive car for about an hour and let it come up to temp
    8. Flush with water and let come up to temp
    9. Drain
    10. Flush with water and let come up to temp
    11. Drain
    12. Fill up with your coolant of choice

    After I did all of this, the radiator came out spotless from my visual inspection into the filler neck

    Car is now running normally and I have heat again.

    • 0 avatar

      I wonder if something like CLR would work as well, or if it would be too strong. Its intended to break up lime scale, calcium, and rust, so it SEEMS like it would be perfect.

  • avatar

    My understanding is that most modern cars use special, nonstandard coolant. Getting the correct fluids are so critical now that it’s a miracle that anything functions.

    The green stuff is effectively dead – however that’s all you can find in the auto parts stores, and that’s all that the tire and lube places will top you off with. I imagine a lot of the Dex-cool problems are related to bogus top-offs with incompatible types.

    “We stock/use universal green here” is the wrong answer.

    And yes, even some dealership service departments will use green stuff and hose water if you ask for a flush.

    The specialty fluids (not just coolant, mind you) have made it the wild west again, so beware.

    There are a few owners wise to this and they make “do not top off” labels for all their tanks (sometimes in sharpie), and whenever I see it- it looks like a bright idea. I guess they handle their own stuff so they can get it right. If that works best for them, why not?

  • avatar
    el scotto

    Thanks for all the info. I see a lot of older Caddys at my local public auto auction. In the back of mind I’m always thinking, “if the interior’s decent it’d make a fun weekend hooptie, even do some work and make it a highway cruiser for the occasional trip”. Then Mr. Lang’s wisdom kicks in and I don’t bid.

  • avatar

    Prestone sells an antifreeze they call extended life. It is yellow and they say it is compatable with others and good for alum engines. They do it for a living and I trust them. I have not had Dex Cool problems tho. I also like the Cascade Dish Powder flush idea. Also I always try to reverse flush without thermostat when I clean my systems.You can do this with by detaching heater hoses and a couple of fittings. Now I have to remember to flush and change my 2002 again before winter.

  • avatar

    I would be diagnosing the code, not focusing on the Dexcool.
    P0128 is generally an overcooling code, unstable temp, tool long to reach normal operating temperature. I deal with this code at work all the time.
    Things to check: 1)Make sure the thermostat is a GM part, not an aftermarket unit.
    2)Check the operation of the cooling fan system, make sure the fan cycles at the correct temperature.
    3)Have a GM dealer check for reprogramming of the Powertrain Control Module
    The PCM is registering a fault code, hence the check engine light. You need to monitor live data stream with a scan tool so you can see what the control unit sees and why the code is being set.

    The days of “Get a code, get a part” are long gone.

    • 0 avatar

      I had this same code with my ’02 Jeep Grand Cherokee. All it was was that the previous owner had replaced the thermostat with a 180F one instead of the spec’d 195F part. When the weather was cold, it never QUITE got as hot as the computer wanted to see, so the code would be set and the CEL would come on. One $11 thermostat and 30 minutes of my time and it was all set.

      I would make SURE that a well-meaning mechanic did not put a too-cold thermostat in there. An awful lot of them seem to think that “colder is better”. Not the case with modern cars.

    • 0 avatar

      Very, VERY good point. I came to my conclusion because the vehicle worked fine for a week, before the code came back on.

    • 0 avatar

      what about a bad temp sending unit turning the fans on too soon?

  • avatar

    I had that same code on my old 2001 Buick. It would come on for a week or 2 and then go off for a week or 2. When I finally got it fixed it was a new thermostat and a new temperature sensor.

    Another thing I noticed while it was happening is my gas mileage went down about 4 mpg.

  • avatar

    Professional cooling system engineer person here…

    DexCool does not like to be exposed to air. You get the oxide buildups (aka “snot”), which clog passages and generally foul up the works.

    DexCool is an OAT (Organic Acid Technology, or as marketroids have it “Organic Additive Technology” because to a marketroid, “acid” is a Bad Word) coolant additive package on top of the standard ethylene glycol base. It was touted as a long-life coolant as it’s similar to the additive package used in heavy-duty engine applications such as semi tractors and industrial powerplants. Couple of minor problems — most of those HD engine applications use ferrous metals in the engines (including the water pumps) and copper-brass radiators, while light-duty vehicles use lots of aluminum parts.

    Once upon a time, the ASTM testing standard water pump for coolant testing was a GM 3800 water pump with an aluminum housing, backing plate (engine front cover) and impeller. When GM released DexCool circa 1995, they changed the 3800 w/p to a cast iron impeller. Why? Based on the testing I was a part of, it was because the aluminum impeller wouldn’t live in DexCool. In some of my own testing, a particularly cavitation-resistant pump I worked on was great on conventional (phosphate-based) coolant additives, but would get cavitation damage with DexCool. Switch back to conventional, and the damage would stop.

    And thus did HOAT coolant (Ford’s Premium Gold, VW’s G12, Mercedes coolant, etc.) come about: Hybrid Organic Acid Technology. Added some of the phosphate additives back into the mix along with a tweaked OAT additive package. You got the long life of the OAT, but with the protection for aluminum that comes from the conventional additive package.

    I love that stuff. If you have a compatible vehicle (pretty much anything newer than 10 years old), it’s highly recommended after a complete flush.

    As far as throwing codes, I agree that the wrong thermostat start-to-open temperature can trip up the OBD-II triggers. The engine calibration is built around a particular engine operating temperature, and if it doesn’t get there, performance suffers.

    There’s a lot of things about automotive engine thermostats — like they don’t actually regulate temperature — that many people don’t realize. They’re technically a thermally-actuated flow control valve. The actual heat flux of the cooling system is a function of heat input and heat output, and except in that ~10F range between start-to-open temperature and full-open temperature, the ‘stat doesn’t actually do much to influence heat flux. Even within that range, equilibrium is dependent not upon the ‘stat, but upon the engine’s heat input and the total amount of heat dissipated (radiator, heater core, some convection and radiation from the engine itself). A typical cooling system sees a 10-15 degF delta T between engine out and engine in once everything is up to temp and in a relatively steady-state operating condition.

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