'05 Trailblazer overheating

TxStetson · Dec 5, 2019

My wife really wanted a Tahoe, but I was an E-5 with 3 kids and a mortgage, and momma didn't work, so there was no way I could afford a $42k SUV at the time. But a little over 3 years later I was an E-7, and GM had a huge military discount so the Tahoe was <$30K.
The Trailblazer we had was an Inline 6 that rattled like an old diesel and got horrible mileage. The Tahoe was a V-8 that got amazing mileage.

oldag · Dec 5, 2019

The V6 they put in the Blazers was trouble free and plenty of power.

Remember hearing complaints about the inline 6 in the Trailblazers.

pronstar · Dec 5, 2019

As an inline-6 fan, I had high hopes for the 4.2 when it came out.

Hard to believe they’d develop, then ditch, an engine within 10 years.

I’ve never owned one, but i seem to recall reading some good reviews...was it really that bad?

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Bozz10mm · Dec 6, 2019

All I remember about the Trailblazer is that it was a stretched Blazer and the inline 6 was rated at near 300 hp. A lot for a 6 cylinder at the time. I think my sister had a new one for a year or so and dumped it because of the bad gas mileage.

JCC · Dec 11, 2019

I have changed the temperature sensor, thermostat, upper hose, lower hose, radiator(broke when changing hoses), water pump and fan clutch. Does not overheat when sitting still for no less than 30 minutes while burping the system. The radiator was open with a no spill funnel, so not under pressure. Test drove after burping and overheated. Took longer than previously. Longer distance. No idea why it is still overheating. Going to take it somewhere for diagnosis. Holds pressure at 15 psi. No leaks now. Just overheating.

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Brains · Dec 11, 2019

Just a question, you didn't remove anything from the front of the vehicle, did you? Specifically the air dam under the bumper (aka. 'the thing that scrapes on stuff') or any of the plastic shrouding around the radiator area?

JCC · Dec 11, 2019

Brains said:
Just a question, you didn't remove anything from the front of the vehicle, did you? Specifically the air dam under the bumper (aka. 'the thing that scrapes on stuff') or any of the plastic shrouding around the radiator area?

I removed the grill, but replaced it after. Why do you ask?

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Brains · Dec 11, 2019

All that plastic up there is pretty important, if you remove certain pieces (depending on vehicle of course) you can actually introduce a high speed / low pressure air zone in front of the radiator and stall any airflow through it when the vehicle is moving. Your mention of it not overheating sitting still, but overheating while driving triggered the thought.

JCC · Dec 11, 2019

I did hit the radiator a little when reinstalling the fan clutch and fan. I would not think enough to cause overheating, but the ridges could use combing. Difficult to avoid other than maybe putting cardboard in front and somehow removing after.

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oldag · Dec 11, 2019

Is the fan clutch engaging when it should? Occasionally new parts will fail out of the box.

JCC · Dec 11, 2019

The fan seems to always be on. Is that how it is supposed to work?

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Brains · Dec 11, 2019

Is it a thermal or electric clutch? Also just because it's spinning doesn't necessarily mean the clutch is engaged, it'll still freewheel to a point. Ideally you'd want the clutch to disengage while warming up, and while moving fast enough that incoming air won't be slowed down by the fan.

JCC · Dec 11, 2019

There is a wiring harness, so I think electric.

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Dad_Roman · Dec 11, 2019

Ok, this is way out of the box.

Do you have the old radiator available still? If so, take it to the water hose and run the hose in it wide open. It should flow out the bottom just as fast as the hose puts it in at the top and NOT fill up.

If the hose catches up and fills the radiator then there is sooo much sludge/buildup that the inside of the engine is also clogged etc and would require a big time flushing procedure.

I had a 05 F150 that did this recently.

JCC · Dec 11, 2019

I do not have the old radiator any longer. It actually was not overheating until I started changing some parts. Was trying to chase a check engine code and changed other parts while I had it taken down.

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Dad_Roman · Dec 11, 2019

Ok. Back to logic.
Gotta have water.

Its gotta flow.

Gotta have air to cool it down.

Im always leery of the thermostat. I say remove the thermostat, drive with out it. Fill with water after starting but before driving because it will afford you immediate flow through the engine so it insures the water side of the equation also. Rev engine (while observing inside radiator) will insure the water pump is actually doing its thing too. Dont get any on ya.

If it overheats then it doesnt have (water) or airflow. If it doesnt? Well then.

I know.....we're chasin after new parts now.

Without starting this elimination process over again it seems like the only thing you didnt do is flush the block out. Everything else is new.

Dad_Roman · Dec 11, 2019

.....and where you at?

Brains · Dec 11, 2019

Do you get heat out of the HVAC like you'd expect? That would indicate you have water flow through the motor and the heater core. With the motor idling, do you see water flowing into the radiator with the cap off? If so, that lets you know the thermostat is opening.

I'm sure this is something "simple" but the tough part of figuring out what piece of the puzzle it is, well that usually isn't the simple part

Dad_Roman · Dec 11, 2019

Yep, try that stuff again^^^^^^^^^

JCC · Dec 11, 2019

The thermostat is the hardest thing to remove and actually has water running through it from the lower radiator hose. See attached.

More fun is I would have to remove the alternator again. That was a pain, especially when the radiator fan shroud was still in place.

I will try to see if heat comes out when running the air conditioning. Heat works great. Pretty sure air conditioning still works.

When I was bleeding/burping the system, I ran the heat so that the heater core would have circulation. I also had the front wheels up on ramps. I revved the engine up some along the way.

I am in Sachse on the Dallas County side.

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'05 Trailblazer overheating

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