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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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Discussion Starter #1
My 02 Bravada had a serpentine belt issue where belt came off one time 4 months ago while driving. Luckily I was 5 blocks from home so I decided to just drive it home (3 minutes). In the driveway, I could hear the coolant boiling and the gauge was about 250F (yikes) so I let it cool down overnight. I got the belt on and everything till this moment still works fine.
Here's a recent coolant temp chart:
54808

I reach operating temp in about 10 minutes city driving (35 mph, no traffic) in 25 F weather. operating temp hangs around 102 C (215 F), and 210 F on highway speed

1) Is my thermostat operating normally or do I need to change it?
2) Is 210-220F in the normal operating range?
3) Did the head gasket got damaged? I still get 20 mpg highway, no coolant mixing with oil, doesn't use coolant (lost about a quart in three months, is this bad?), BUT my CAT died a month ago so I'm not sure if its related the overheating incident or the abuse from previous owner
4) Previous owner had regular coolant. What do you guys think about a flush and filling her up with dexcool?
 

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2004 gmc envoy_slt
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2,283 Posts
How are you measuring the coolant temp? Dash gauge or scan tool? Your temp sounds OK if you're reading just tje dash gauge (normal temp with scan tool is usually around 195 deg.) What do you mean by "regular coolant"? These engines should have Dexcool installed. A partially clogged cat can elevate coolant temp somewhat.
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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26 Posts
Discussion Starter #3
I am reading with a scan tool. The previous owner replaced the water pump but he used the polyethylene glycol based coolant (green). How do I know if my cat is partially clogged? I know that my oxygen sensors mirror each other (see picture), but I'm not sure if that automatically means that its clogged.

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2004 gmc envoy_slt
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The O2 sensors should not "mirror" each other. The O2 sensor on the exhaust manifold should cycle up and down, but the one after the cat should remain fairly steady. Your condition shows that the cat is not functioning.
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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26 Posts
Discussion Starter #6
The O2 sensors should not "mirror" each other. The O2 sensor on the exhaust manifold should cycle up and down, but the one after the cat should remain fairly steady. Your condition shows that the cat is not functioning.
I am aware that my cat is dead. I'm not sure what killed it before I go one and put a new one.
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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26 Posts
Discussion Starter #7
how do you know the cat is dead?

what scan tool and app made that chart?
Cat is dead because the exhaust (downstream) oxygen sensor should have a steady voltage and not be identical to the upstream sensor.
App is Car scanner on android and tool is ELM327
 

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2008 gmc envoy_sle
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629 Posts
thank you for the Car scanner info. very helpful, as i am looking to replace my older innova obdII scanner.

let us know what happens when you replace the o2 sensor.
whats the current mileage of your Bravada 4.2?
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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26 Posts
Discussion Starter #9
thank you for the Car scanner info. very helpful, as i am looking to replace my older innova obdII scanner.

let us know what happens when you replace the o2 sensor.
whats the current mileage of your Bravada 4.2?
The o2 sensor is probably fine. Its most likely that the catalytic converter is bad. Im at 235,000 now
 

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2004 chevy trailblazer_lt
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63 Posts
doesn't use coolant (lost about a quart in three months,

Not sure what you mean ? You are losing coolant ? Or not ?

Might be what has ruined your Cat conv. possibly from blown a head gasket


One way to check for bad head gasket is to see if combustion / compression pressures are escaping into the cooling system
1. With a * Cold * engine remove the Rad Cap and top off with water if low

2. Disable prior to cranking engine by removing the fuel pump relay to prevent starting

2. Have someone crank the engine while being careful not to look directly over the top of the Rad filler neck

3. Observe for bubbles or coolant being ejected from filler neck
Result ? If its bad it will spew about

4. If coolant does not eject or bubble then its safe to assume the head gasket is ok.

* Also could see white smoke and smells sweet if antifreeze was being burned off, just be sure normal moisture / condensation is removed from exhaust system first

A cooling system pressure tester will confirm results as well :)
 

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02 Oldsmobile Bravada, 235,000 miles, vortec 4.2L
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Discussion Starter #11
Not sure what you mean ? You are losing coolant ? Or not ?
I cant remember where the level in the expansion tank was at, but when I checked it this week it was low. I also have a crack at the top of the expansion tank (that I duck taped lol) so I don't know if its burning coolant or its evaporating from the expansion tank. Radiator is at level though.

One way to check for bad head gasket is to see if combustion / compression pressures are escaping into the cooling system
1. With a * Cold * engine remove the Rad Cap and top off with water if low

2. Disable prior to cranking engine by removing the fuel pump relay to prevent starting

2. Have someone crank the engine while being careful not to look directly over the top of the Rad filler neck

3. Observe for bubbles or coolant being ejected from filler neck
Result ? If its bad it will spew about

4. If coolant does not eject or bubble then its safe to assume the head gasket is ok.

That's interesting.I did a coolant flush a while back and when I was trying to bleed it I haven't seen any bubble coming while the engine was running. Maybe that's a good sign. Also, do you think a block testing fluid work instead of this trick?

* Also could see white smoke and smells sweet if antifreeze was being burned off, just be sure normal moisture / condensation is removed from exhaust system first

Condensation
lasts a bit here in iowa but nothing more than 10-15 minutes. Havent paid attention to the smell 😅

A cooling system pressure tester will confirm results as well :)
Heck, I'll do a compression test as well.
 
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