Sonoma 4.3 Vortec Intake/Head Gasket Replacement

[rharris]

2001 Sonoma 4.3 with 149k. We have had the truck since 2018 @ 146k. The truck always seemed underpowered and over thirsty. Anyway, two months ago and two days after passing his drivers test, my sons Sonoma heat quit. I reverse flushed the heater core and it cleaned out some black gunk and heat would work. Repeated this every other day for about a month. Replaced thermostat a few times, ran flush through multiple times, replaced overflow tank due to crud baked in the bottom, and could not get the gunk off the radiator. You could stick your finger in and get sludge off radiator. I assumed the radiator was gunked up from the last 20 years. I replaced the radiator and had heat for a week, and then the tstat blocked up and heat quit. New radiator looks like its on its way to the old radiator. After reading, it sounds like the intake gasket could be the culprit. The oil looks normal. the coolant is crudded up again. The 2 plugs i pulled are clean and dry. Picture below is the new radiator with some crud scraped off the plastic to give an idea of what the contamination is. The side mark is a marker. A few questions -

1 - The sludge in the coolant does not seem to be oil, and appears to be carbon-like. Does this support the intake gasket failure?

2 - why hasn't the coolant contaminated the oil if there is a leak?

3 - Are these engines as prone to head gasket failure as intake? I have the gaskets for the heads as well, just not sure if I want to pull them off. Gasket kit is Felpro

4- GM repair manual says to use angle settings for head/intake bolt torque (have new bolts). Is this crucial, or is a ft-lb torque wrench sufficient.

5- Any other suggestions on the problem before I go tearing it apart?

6- Is Dexcool necessary in GM?

[95 S_Trucker]

Intake gaskets are common. Head gasket failures are relatively rare. The gunk is from someone mixing dexcool with another coolant in the past. It will take a lot of flushing to get everything clean.

[rharris]

Flushed for hours on multiple days and put all new coolant, hoses, and radiator. I thought the gunk would’ve been cleaned out by now, but maybe not.

[95 S_Trucker]

It’s stuck on every surface inside the cooling system. The engine block, heads, heater core, all of the hoses.

I had a 99 2 door blazer, it took me 6 months, a radiator, and a heater core to get the cooling system clean.

[rharris]

Strange that we had it for a year and a half and it was fine. Any luck with radiator flush? I used royal purple and blue devil, neither touched it. Friend said to use purple power degreaser.

[rharris]

Are the spiders normally this cruddy? Intake gaskets have already been done. It looks like it was leaking at the back of the head on both sides due to the milky color. Any thoughts?

[OL SKOOL]

Those injection spiders always get that black grunge on them. If they have any miles on them. I have used Dawn dish wash soap have had good luck with it . Put a flushing tee in heater hose and flush while running. They are famous for intake gaskets. Usually when head gaskets go they over heat.

[rharris]

After gallons of flushing, refilled with Peak coolant. No more dexcool. I can still see some grime in the system, but no blockage of T-stat or heater core for over a month.