By on April 11, 2013

Scott writes:

Hello –

Saw a Dex-cool question you posted previously, and figured I would try my own. We have a ’06 Malibu Maxx SS. Basically the car runs hot, but not all the time. I have been religious about flushing the cooling system and using only the correct fluids.

It has 91k, and I’ve read online that they tend to run a little above avg temp. Like your CTS questioner, this car was clearly driven hard before we bought it, but nothing horrible. It doesn’t throw any codes and doesn’t get into the red, but its definitely high according the gauge. On the highway it tends to sit right in the middle. If it sits in traffic it will rise a little, if I drive it hard it will shoot up but eventually come back down.

The water pump was recently replaced, but otherwise we have had no real problems with the car (aside from the usual crappy GM build quality, ISS, and lots of brake pads). I just ordered a new t-stat, figuring that was a cheap fix to try.

The car is paid off and I would like to keep it for a while, but I am worried putting my wife and daughter in this thing in the heat of summer, or going on a road trip, etc.

Sajeev answers:

So this Malibu was driven hard before you got it, but you’ve been good about respecting The Dex-Cool Monster…not letting the system get contaminated.  This means, depending on when you bought it, the previous owner coulda mixed fluids. And mildly gunked up the system.

See how being an Internet Automotive Mechanical Detective works?

More to the point,“if I drive it hard it will shoot up but eventually come back down” points to a partially clogged radiator. Partially clogged because of mild gunk accumulation.

When we’re talkin’ about a two-owner vehicle running Dex-Cool…well, I’m just being my typical snarky, untrustworthy self. No detective work there.  Radiators do go bad over time, failing more epically when sporting partially plastic construction too.  The water pump?  Not super-likely, unless the vehicle has plastic impellers (cough, VAG products) and they are crumbling to bits.  The electric cooling fans?  Probably not: they are merely less effective when pushing/pulling on a cloggy radiator…so the recovery time from hard driving is longer.

You can flush the radiator, or have a local shop do it for you. Or for added piece of mind: eliminate a known wear item on aging vehicles by spending all of $100-150 on a new one from an on-line parts vendor. I’d just order a new one and be done with it.


Send your queries to [email protected] Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

Get the latest TTAC e-Newsletter!

21 Comments on “Piston Slap: Cooling to the MAXX?...”

  • avatar

    Just as a precaution, put in a new thermostat and see what happens. Can’t be more than $20 for a new one, unless it’s a some newfangled thing that some newer cars have these days. If that doesn’t do it I’d look into a radiator flush.

  • avatar

    Rught…Do the thermostat first. I doubt thats your problem,but it can’t hurt to change it.

    As a long time GM owner, I would be willing to bet,that your rad needs to be replaced. Not so long ago thier was rad shop,and muffler shop on every street. Modern enginering, and materials, have just about cured rad, and exhaust system issues.
    Your rad may not leak, and it may look pretty good. Fact of the matter is,its not working the way it should. Replace it,and don’t buy a used one.

  • avatar

    I flushed and ran some cleaner through the cooling system of my aging ride a few months ago since I had it drained to replace a leaking oil filter adapter plate (which the lower radiator hose routes through) gasket. I was thrilled, after flushing a ton of gunk out of the heater core, to get good strong heat back again just in time for the what passes for winter down here in the south. I was bemused and slightly less thrilled to discover that cleaning the system also dislodged the accumulated gunk that was plugging a tiny hole in the radiator so now I usually find a few drips on the ground under the nose of the car and I have to add a cup or so of water to the overflow tank every few weeks. Oh, well. I was hoping it would plug itself up again before summer forces me to deal with it.

  • avatar

    Nice ride. I almost got one myself.

  • avatar

    You have an air pocket in your cooling system. I have seen this on numerous 3500/3900 equipped GM products after the cooling system has been opened up for any reason such as t-stat replacement, coolant replacement etc. Fill the radiator up until you can see the fluid and let all the bubbles surface. The fluid will then go down. Repeat until the bubbles stop. Start the engine and repeat above until the bubbles stop. You may also have brass bleed screws either on your t-stat cover or near the heater hoses. They should be up high and in plain view. These will also need to be loosened when the fluid is full. The more air you get out the better. I have only worked on the Impalas and some of the older 2001-2005 cars but your Malibu will probably have the bleeders. Get all of the air out and then test drive the car for a good 50 miles or so and observe the gauge. If this doesn’t cure the issue then perhaps your radiator is bad but I have yet to replace one on any 2000-2009 GM product I have worked on with this issue.

    • 0 avatar

      I’ve had to do this a couple of times with our ’07 Impala. No problems with it running hot but in the winter you get cold air instead of heat from the heater at idle as that pocket of air likes to make itself at home in the heater core when there’s not a lot of flow in the coolant. As soon as you step on the gas you hear a bunch of burbling behind the dash and then you start getting heat again – come to a stop and it’ll gradually start blowing cold again.

      I pull it up on some ramps and let it run for a while and then leave it parked there overnight to let all the air collect at the top. Raise the RPMs for a while too to get the flow going to push those bubbles out from their hiding places.

    • 0 avatar
      Steven Lang

      Dealt with the same issue on an 05 Malibu Maxx LS about a year ago. These vehicles like to be ‘burped’. So long as the Dex-Cool is changed every couple of years, you usually don’t get a substantial gunk accumulation.

      But don’t be surprised if that coolant reservoir become a quite gunky by the time you hit 120k and at that point, you’re just better off dismantling the whole cooling system and replacing the whole thing with new OEM-level parts.

      Avoid the cheap water pump / radiator / t-stat on the Malibu. The 3.5 Liter is an excellent motor but no engine can withstand the corrosive effects of neglected Dex-Cool and a plastic lower intake manifold.

    • 0 avatar

      I concur with ponchoman’s assessment of air pockets. If you have trouble bleeding it, pulling a slight vacuum on the system can help get it out. There are attachments for hand held vacuum pumps that fit on the radiator or degas fill points.

  • avatar

    Check carefully the finned area on the front of the radiator. You may have accumulated enough dirt, soot, gunk to have clogged the external air passages, rather than the internal Dec-cool coolant channel clogging. Or, and here’s the bad news, it could be a bit of both problems. If the car’s a keeper, a new radiator will save a lot of grief.

  • avatar

    I wonder if GEOZINGER had this problem with his Malibu Maxx he said he once owned?

    At least the temp gauge doesn’t hop around on you, indicating a head gasket failure. My old Chryslers were good at that. I don’t own them anymore…

    • 0 avatar

      Hey Zackman! I thought I heard someone calling my name…

      My Maxx was a lease vehicle, so at the end of our three year stint with it, we gave it back. The only real trouble we encountered with that car was the intermediate steering shaft and a squeaky headliner.

      But from the sounds of it, there’s air in his system. This could happen to any car…

  • avatar

    Radiators seem to have gone down in price over the years, so I’d replace it and the thermostat.
    Intersting ride the MAXX SS. I had a Maxx and thought the packaging was brilliant, the interior, build quality and materails – not so much. I wish this body style had caught on though, more useful space than almost any CUV and many SUVs.

  • avatar

    Funny you should call out the VAG plastic impellers. My beloved B5.5 Passat ate it’s impeller on the way back from Easter. Cost to replace the water pump? 700 bucks (and yeah, I did the timing belt, water pump, etc etc approx 50k ago).

    Needless to say the Passat now has a new owner and I am the proud owner of a Performance Blue ST.

  • avatar

    Professional Cooling System Engineer here…

    I’d be inclined to think it’s got air in the system, as others have said. At low engine speeds/loads, it’s not enough to cause a problem, but at higher speeds, the air pockets tend to serve as roadblocks to proper heat transfer, plus they can get pulled into solution with the liquid coolant, lowering its efficiency.

    Jeeves, those early VAG plastic impellers are utter crap. There are good plastic impellers out there (I’ve designed a few), but those aren’t them. :)

  • avatar

    We have a 2005 Malibu LS 3.5l with 147k on it that has always run warm under certain conditions. Stop and go traffic with the A/C on for example. Then when you get moving it’s fine. It’s been doing this for as long as I’ve owned the car beginning at 62k and I have steadfastly ignored it to no ill effect.

  • avatar

    Before you sink money into a new radiator I would hook up your OBDII scanner and keep an eye on the actual coolant temperature while driving, dash gauges aren’t known for their accuracy.

  • avatar

    get yourself a $15 infrared gun thermometer from amazon, and play with it. shoot it at the top and bottom radiator necks, the hoses, thermostat housing, etc.

    it should be markedly cooler coming out the bottom than going in the top. radiator caps also age badly and are cheap.

    might be worth pressure checking the system and cap

  • avatar

    Was it doing this prior to the water pump replacement? If not then I’d say it is likely air but if so then I’d go with the radiator unless someone else had the cooling system open.

  • avatar

    I was terribly disappointed when the Maxx failed. I liked the size, the package, the clever and fiercely practical moving back seat.

    Why do Americans demand SUVs? Is it the great handling that the high center of gravity gives them? Is it the superior fuel efficiency of a tall, high frontal area vehicle?

Read all comments

Recent Comments

  • EBFlex: https://dictionary.cambridge.o rg/us/pronunciation/english/al zheimer-s
  • dal20402: How do you pronounce “Xiden?”
  • Carlson Fan: When the F&I guy tried to sell me an extended warranty on my used Volt I just told him all the money...
  • 28-Cars-Later: “The F&I guy didn’t even bother to try to sell me anything additional.” Yes because...
  • 28-Cars-Later: Proper f***ed.

New Car Research

Get a Free Dealer Quote

Who We Are

  • Adam Tonge
  • Bozi Tatarevic
  • Corey Lewis
  • Jo Borras
  • Mark Baruth
  • Ronnie Schreiber