Hi Everybody!

Although I have been reading all of the great tips and advice in this forum for several years, I just became a member and this is my first post. I have a 2003 GMC Sonoma (VIN X) with a 4.3L Vortec and ZR2 package with ~70,ooo miles. Besides eating me alive by guzzling gas, it has been pretty good to me except for issues with the cooling system (thanks to Dex-cool) and the instrument panel cluster (which I will ask about in Lighting and Electrical).
I learned all about Dex-cool the hard way a couple of years ago, after having to travel 100 miles in sub-freezing temps with no heater. By flushing the crap out of cooling system, especially the heater core, and replacing the Dex-cool with Peak antifreeze (that is supposedly "compatible for use in all automobiles and light-duty trucks, regardless of make, model, year or original antifreeze color"), I thought that I had resolved this issue.
To my dismay, this problem reared its ugly head, again, a couple of weeks ago when I started smelling antifreeze when I ran the fan. Unfortunately, I have not been able to monitor my coolant temp or get any warnings because my instrument panel does not work. When my engine would not start, apparently because it was overheated, I let it cool and took the cap off of the radiator to find that it was virtually empty, except for rust-colored sludge, despite having plenty of (dirty) fluid in the reservoir.
After adding about a gallon of anti-freeze and water, I drove home and found a leak in the driver-side of my radiator about 3 fins down, and I found signs of a leak on my lower intake manifold. From advice I have read in this forum, I have not driven it, and I will be replacing my manifold gaskets, radiator & cap, thermostat, water pump, and a few hoses too. I know that I need to flush out everything A LOT, too.
I am not sure which I should do first because I don't want to 'flush' anything into my engine block if there is an interior leak, and I also don't want to foul up my new cooling system components with sludge. I would also like to know what else I should do (besides change the plugs, wires, distributor, and rotor) while I do this work. Finally, I am not sure if I should replace the head gasket while I am at it, in case Dex-cool has damaged it, too.
Please pardon the verbose post, and I hope that I didn't simply overlook the answer somewhere else in the forum. I am really looking forward to finding out what y'all have to say about this and a few other (hopefully more concise) questions. Thank you for taking the time to read and/or answer my questions!

 

Meh.

this is 2 issues.

dexcool is fine. problem is,over time over 100k miles,nobody flushes it out like they need too,and then it eats gaskets etc. then they complain on dexcool.

the sludge,flush it out the best you can. Dont touch the headgaskets. If no waters in oil and the exhaust is clean. they are fine.

lower intake,thats normal for these things dexcool or not. thats just the way these later 4.3s work. replace em,move on.

flush the cooling system,dump in green. or flush it and run dexcool. doesnt matter boths fine. just dont mix them.dexcool is just as good as green,but over high miles it goes bad and causes issues.

 

Thank you, Chris015!
I appreciate your input. I think you answered my main question, which I may have obscured by the rest of my long-winded post. If I understand you correctly, you are advising me to change the intake manifold gaskets before flushing the cooling system, and you're telling me not to worry about the head gaskets unless I see evidence that water is in my oil.
I have seen some folks flush before changing their leaking gaskets, in order to clean out as much sludge as possible before opening the intake. After reading a bunch of stuff about how coolant/water/sludge can get in other parts of the engine and cause major damage, I decided that it may be a better idea to fix the leaks before flushing. Thanks again for your answer!

 

There are two main problems with using ethylene glycol in 1996 and newer 4.3's: #1 Although it does protect against freezing and boil over, it does nothing to protect aluminum against electrolysis, which is what destroys the radiator, heater core, and lower intake manifold. #2 It contains an abrasive material that will destroy the water pump seals.

As Chris mentioned, Dexcool needs to be flushed every 3 years or 36K miles, (ethylene glycol needs to be flushed every year). If it is neglected, Dexcool breaks down and loses its ability to protect the aluminum, (that's when the problems start). Dexcool should be diluted 50/50 with distilled water, and no other types of coolant should be added, especially ethylene glycol, unless you want mud in your cooling system

The sludge clogged up your radiator cap, that's why the radiator was empty and coolant was still in the reservoir. As the coolant expands and contracts, the radiator cap allows it to transfer back and forth. If it's clogged, it can't transfer.

In your case, you probably ought to remove both heater hoses from the core, and both radiator hoses from the radiator. Then blast the weenies out of each hose with a garden hose until it comes out clear. In some cases, a power washer works well too Might take a few times if it's really sludgy. Flushing all that crap out is no easy task, so don't get frustrated if it doesn't clear up right away. When you remove the lower intake manifold, you can use a spoon to scoop out the crap from the coolant passages.

The coolant odor when you turn the fan on, is most likely a leaky heater core, also from electrolysis. If the core is leaking, it needs to be replaced. A leak in the radiator fins means it's time for a new radiator, (could also be from electrolysis).