Engine Top End

[xintersecty]

Possibility of a bad thermostat is high. Was this a one time thing, or does it always overheat now? how hot is overheating? how did you know?

Its not likely that the radiator is clogged, but it is not out of the question. If you ended up empty, it could be a leak. Which a slow leak is hard to detect, but a long road trip will make it steam out.

All, I appreciate the suggestions. I suspect the Rabbit is right. Before the road trip it would heat normally. Of course I had not long distance test the rebuild. On our way back, I noticed the overheat signal and then I saw the fluid had steamed out. At that point I used resources at hand and until I got to a convenient store to buy some premix antifreeze.

Now it consistently overheats. Just city driving runs the temp above normal. One of my other issues is a leak around the exhaust header. I need to pull the heat shield and see if can find the leak before I pull that off.

So I can watch the temp gauge and see blips in the needle as the water is released from the head into the radiator. So I think the t-stat is working. I have not checked the hoses for a pressure differential as WyrTwister suggested.


While the radiator could be the source of blockage, something in the head could be causing it too. I need to make sure everything else is good before I pull the head again.

[WyrTwister]

Exhaust leak around the exhaust manifold or coolant leak ?

How difficult would it be to temporary remove the tstat and test it w/o a tstat ?

Can not remember you saying ? Was the water pump replaced ? It is driven by the timing belt ?

Might be worth investing in ;

Search results for: 'infrared scanner'

Help you do some tracing ?

God bless
Wyr

[WyrTwister]

You can test the tstat , itself , by placing it in a pan of boiling water & seeing if it opens .

God bless
Wyr

[xintersecty]

The latest updates.

I had a bad TSTAT that was causing the overheat. I took the TSTAT out, pulled the rubber gasket, and used on my old one. The old TSTAT had a slightly thinner gasket causing it to leak around the TSTAT housing. No more overheat issues.

I found the issue to the exhaust problem. It was my own silliness and lack of attention.

I remember wondering where was the washer for the nuts. Well I found them on top of the gasket when I took off the header.
Here is the exhaust pattern it created


While the header was off, I took no chances this time and cleaned it good (it's a southern thang).
before


After cleaning with a belt sander


Now down to error codes, need to pull the sensor and check wiring as both is saying low voltage.....hmmmm

[06T200]

Maybe you forget one of the O2 sensor connections?

I have seen P2077/2076 pop up on my LS a couple of times, right after getting it back on the road, but it seems to resolve itself the next day. Sometimes they self heal I guess lol
DTC P2077:
Intake Manifold Tuning (IMT) Valve Position Sensor Circuit Low Voltage

[xintersecty]

Can't forget an O2 sensor. both are plugged in the harness. I will have to mess around with the cables and make sure everything is connected. The manual is not clear that the IMT is the same as absolute pressure sensor. I am going to say yes as that is a very logical choice to measure the pressure and then re-tune with a flappy thingy. I did spay a lot of cleaning crap in my intake manifold so could have killed that sensor:

[06T200]

Here is the scoop from TIS on the IMT contraptions:

The engine control module (ECM) supplies the intake manifold tuning (IMT) valve position sensor with a 5-volt reference circuit, a low reference circuit, and a signal circuit. The IMT valve position sensor provides a signal voltage that changes relative to the IMT valve angle.

P2077
The ECM detects that the IMT valve position sensor is less than 0.3 volt for 5 seconds.


Here is the connector diagram for IMT pos sensor.




1. Ignition OFF, disconnect the harness connector of the IMT valve position sensor.
2. Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal 3 and ground.

If greater than 5 ohms, test the low reference circuit for a short to voltage, or an open/high resistance. If the circuit/connections test normal, replace the ECM.


3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and ground.


4. Verify the scan tool IMT valve position sensor percentage parameter is less than 5 percent.



5. Install a 3A fused jumper wire between the signal circuit terminal 2 and the 5-volt reference circuit terminal 1. Verify the scan tool IMT valve position sensor percentage parameter is greater than 95 percent.



6. If all circuits/connections test normal, replace the IMT valve position sensor.

[06T200]

GM part number for the sensor: 96859269

[xintersecty]

Can't forget an O2 sensor. both are plugged in the harness. I will have to mess around with the cables and make sure everything is connected. The manual is not clear that the IMT is the same as absolute pressure sensor. I am going to say yes as that is a very logical choice to measure the pressure and then re-tune with a flappy thingy. I did spay a lot of cleaning crap in my intake manifold so could have killed that sensor:

While the plugs for the O2 sensors are in your face in the engine compartment the plug for the IMT is not obvious. I found it buried down under a bunch of hoses and alas I missed. Plugged it in and P2077 code went away. The O2 sensor is a still a problem. I might get a new one as the old has quite a bit O'Carbon on it.

[xintersecty]

Got a new O2 sensor to work out the last two bugs. Bought a generic Bosch from advance auto.


Installed it, cleared codes and will report in after a couple days running.