Sudden overheating

[wsryan]

My 2004 TB V8 has on 4 days overheated, each time separated by about a week. Seems to occur suddenly, then if I shut it off and allow it cool, it goes fine again until a week or so later. Can the thermostat stick closed, then relax and open when everything cools off? Someone suggest the coolant temperature sensor could be bad--I have not idea where that is, or its function?

 

[The_Roadie]

Does it drive or act or feel hot under the hood like it's overheated? If it does, then suspect the thermostat, although ours tend to stick open a lot more often than they stick closed. Could also be a soft/collapsing hose. Have you squeezed the hoses to check? How many miles, and did you change the coolant at 100K if you're over that?

 

[wsryan]

You know, I haven't actually had time when it has behaved this way to be able to check--it has happened just as I arrive at a location for a meeting or something, without fail (except for the day it happened to my wife). I have been able to stop and shut it off.

And when you say to check the hoses, just do that anytime, to see if they are soft and collapse easily?

I have about 175K on it; it was flushed and refilled, probably around 130K. There is all kinds of the creamy, thick gunk that piles up in the reservoir. Does that mean anything?

 

[wsryan]

So, the last two times this thing has overheated, I have been running the heater on high and noticed that it begins blowing cold air on my feet, then within a couple of minutes, begins to overheat. Water temp will fluctuate between 235 and 260, then the engine overheating warning comes on.

What is the connection between the cold air from the heater and the subsequent coolant overheating?

 

[Voymom]

So, the last two times this thing has overheated, I have been running the heater on high and noticed that it begins blowing cold air on my feet, then within a couple of minutes, begins to overheat. Water temp will fluctuate between 235 and 260, then the engine overheating warning comes on.

What is the connection between the cold air from the heater and the subsequent coolant overheating?

A lot of times when a vehicle is over-heating you can turn the heat on to cool off the engine. How is the water pump? Coolant level?

 

[The_Roadie]

Could be thermostat stuck closed. Check the hoses and radiator temps (top/bottom) safely if it happens again.


Ahhhh, on second thought - a closed thermostat still allows cabin heat on cold days. The water pump may be dying. Internally where you can't see it.

 

[meerschm]

You know, I haven't actually had time when it has behaved this way to be able to check--it has happened just as I arrive at a location for a meeting or something, without fail (except for the day it happened to my wife). I have been able to stop and shut it off.

And when you say to check the hoses, just do that anytime, to see if they are soft and collapse easily?

I have about 175K on it; it was flushed and refilled, probably around 130K. There is all kinds of the creamy, thick gunk that piles up in the reservoir. Does that mean anything?

Creamy does not sound good.

You need to figure out whatisgoingon before the engine quits

 

[wsryan]

Thanks, guys. I think I will go ahead and change the water pump, and the thermostat while I am there.

Any posts on the quick and easy way to change out the water pump?

 

[The_Roadie]

We had one back on trailvoy, easily found using Google: How to replace water pump (pics) - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum

 

[Voymom]

I would just be very careful with those bolts...It's NOT fun at all to break them in the engine block, and I would make sure you had a set of easy out's on hand just to be on the safe side, we didn't even make it to torque before they snapped either, so tread lightly.

 

[wsryan]

OK-so I changed the water pump and the thermostat. Still behaves the same...or I guess that would be misbehaves the same way.

I warmed it up once, let it cool and topped off the coolant in the radiator again. Still only put a little over a gallon or so in.

But once it starts overheating, it pegs it--not just a little warm.

The coolant sensor can't have any bearing on this, can it?

Still acts like there is no water circulating in the engine??? New thermostat...could the water jackets be completely clogged, or something like that???

 

[BRomanJr]

OK-so I changed the water pump and the thermostat. Still behaves the same...or I guess that would be misbehaves the same way.

I warmed it up once, let it cool and topped off the coolant in the radiator again. Still only put a little over a gallon or so in.

But once it starts overheating, it pegs it--not just a little warm.

The coolant sensor can't have any bearing on this, can it?

Still acts like there is no water circulating in the engine??? New thermostat...could the water jackets be completely clogged, or something like that???

Does it behave (not overheat) when you are moving? (getting airflow through the radiator).
Unlikely to be clogged water jackets.

If the fan clutch is not working properly and the fan is not spinning fast enough, it may only overheat when sitting still. In this case you should get a code for improper fan speed.

If you check it cold, is the radiator full to the top? Air in the system is the most likely problem.

 

[meerschm]

how did the coolant look? did you figure out what was giving you the creamy gunk? did it look like some of the same when you had the thermostat and water pump out?


you could try to idle it with the radiator cap off, and see if coolant is moving. (make sure not to open while it is hot, open when cool and run to warm it up) Normal operation would be to not see any motion in the radiator until the engine gets to operating temp, then you should be able to see some movement, and feel the temp warm up as the thermostat opens and lets hot coolant enter the radiator. if there is any air in the coolant system, some discussion that you may see the level rise and fall as bubbles move out.

do you have a way to measure the temps besides the sensor? (I have an IR thermometer I can point at things to measure temps)

http://www.harborfreight.com/mercha...tech/non-contact-laser-thermometer-96451.html something like this.

you may want to determine if the overheating is real or just the sensor.

it is possible also that you have some kind of software/computer issue, since the instrument panel temperature indicator is driven by the computer, and the various temperature control doors are also computer controlled. I am not sure what the software does if it thinks the engine is overheating.

first step would be to verify the coolant is circulating, and warming up normally.

do you have a way to read the OBD? it would let you read the temp sensor readings, and watch them move as the engine warms up.

 

[wsryan]

So, it seems that the air in the system was the problem. I am way too old to be doing this stuff myself apparently. When did "burping " the system become necessary anyway? I never had to do that in the 1960s

So, on my initial test run after my amateur attempt at burping it, it seems to be good. Did not get over 210 degrees, was blowing nice hot air (which it sounds like I will need for the ice and snow heading my way tomorrow).

Thanks to everyone for their input--I do appreciate it immensely!

I will be back if it acts up again in the next few days.

 

[meerschm]

So, it seems that the air in the system was the problem. I am way too old to be doing this stuff myself apparently. When did "burping " the system become necessary anyway? I never had to do that in the 1960s

So, on my initial test run after my amateur attempt at burping it, it seems to be good. Did not get over 210 degrees, was blowing nice hot air (which it sounds like I will need for the ice and snow heading my way tomorrow).

Thanks to everyone for their input--I do appreciate it immensely!

I will be back if it acts up again in the next few days.

Glad you figured it out.

don't feel bad, you are not the first DIY'r to change out things that were not needed on the way to finding the real problem. the price we pay for saving a few bucks, learning, and having fun off the couch in front of the TV.

my impression is that the need for burping comes from stretching the engines to fit in smaller cars. (not as easy to put as big an engine as desired in a small enough space.) not the end of the world, but does add an extra step.

 

[meerschm]

Nagging question, how did the bubble get there in the first place?

you might have a leak someplace.

just have to keep an eye on the coolant level.

 

[wsryan]

I'm sure I have a leak in the rear heater core or lines, but haven't gotten deep enough or motivated enough to expose that yet, plus it has sounded like the costs of repairing a small leak back there would probably not be worth it. I smell antifreeze if the rear blower is running at a higher speed than the front, but have never seen a drop on the garage floor, and have never thought the coolant level was low enough in the reservoir to think I had a significant leak. The only hint I would have had was the sweet smell of antifreeze...

 

[meerschm]

I'm sure I have a leak in the rear heater core or lines, but haven't gotten deep enough or motivated enough to expose that yet, plus it has sounded like the costs of repairing a small leak back there would probably not be worth it. I smell antifreeze if the rear blower is running at a higher speed than the front, but have never seen a drop on the garage floor, and have never thought the coolant level was low enough in the reservoir to think I had a significant leak. The only hint I would have had was the sweet smell of antifreeze...

so do you think the leak allowed air to enter the system, since it was easier to pull air thru whatever leaks than pull coolant from the overflow through the rad cap?

or did enough leak out to pull air through the overflow?

if the overflow is not going down, you may have to burp the system more often to get rid of the air that gets in.

sooner or later you may have to fix the leak, or bypass around the rear circuit with some heater hose. it is not really healthy to breathe that stuff.

- - - Updated - - -

I'm sure I have a leak in the rear heater core or lines, but haven't gotten deep enough or motivated enough to expose that yet, plus it has sounded like the costs of repairing a small leak back there would probably not be worth it. I smell antifreeze if the rear blower is running at a higher speed than the front, but have never seen a drop on the garage floor, and have never thought the coolant level was low enough in the reservoir to think I had a significant leak. The only hint I would have had was the sweet smell of antifreeze...

so do you think the leak allowed air to enter the system, since it was easier to pull air thru whatever leaks than pull coolant from the overflow through the rad cap?

or did enough leak out to pull air through the overflow?

if the overflow is not going down, you may have to burp the system more often to get rid of the air that gets in.

sooner or later you may have to fix the leak, or bypass around the rear circuit with some heater hose. it is not really healthy to breathe that stuff.