acid flushing radiator cooling system

Well the Jimmy's starting to overheat irradically again.

I've replaced just about everything in the cooling system within the last year (stat, "Stant" brand rad cap, water pump, radiator) and flushed it recently. Even after that thorough flush about 5 months ago, I recently noticed sludge floating around in the overflow reservoir. Sometimes the truck will run fine and sometimes it will run too hot. I always shut it off if it goes about 1/2 on the temp gauge. Anyhow, I think that the irradic overheat is caused by a large chunk of rust/scale/sludge/gunk getting
stuck periodically - usually in the thermostat or in the heater core.

Anyways, there were some previous posts about acid-flushing a system. I can't seem to find any acid-based flush products at Autozone, Advance, O'Reilly, etc. Is an acid-flush something that a do-it-your-selfer can do? I've heard an acid-flush is primarly oxalic acid. Is there a name-brand acid flush product?

Any negative thoughts on acid flushing?

Acid flush is the best. Stop by a local rad shop and ask where they get their stuff at.

Well, I found it at another O'Reilly's Auto Parts. It's made by Prestone and comes in a very plain yellow canister. It's active ingredient is indeed oxalic acid rather than the citric-based acid in their normal flush product. The top half of the container holds the acid in powder form - the bottom half of the container holds the neutralizer.

Swish n' Gargle. Rinse n' Repeat.

I'll give it a try in a day or so ...

Acid flush is the best. Stop by a local rad shop and ask where they get their stuff at.

Well, I did the acid flush today. It took a long time but I followed the directions to a "t" (drain, fill with acid and H2o, run for 1 hour, cool/drain, add neutralizer and run for 10 minutes, cool/drain, flush with H2o until clear, refill with coolant - thorough clean of reservoir). The only thing I did different from the directions is that I took the thermostat out completely. I reinstalled it when finished.

So far, so good ... will keep an eye on it ...

be careful with this stuff folks (oxalic acid) ... don't inhale or touch it ... dont inhale it in its powder state ... don't inhale the steam once it's gone thru your cooling system ... let things cool off !!! don't let it touch your paint ! Soapy water should neutralize ... just be careful ...






Well the Jimmy's starting to overheat irradically again.

I've replaced just about everything in the cooling system within the last year (stat, "Stant" brand rad cap, water pump, radiator) and flushed it recently. Even after that thorough flush about 5 months ago, I recently noticed sludge floating around in the overflow reservoir. Sometimes the truck will run fine and sometimes it will run too hot. I always shut it off if it goes about 1/2 on the temp gauge. Anyhow, I think that the irradic overheat is caused by a large chunk of rust/scale/sludge/gunk getting
stuck periodically - usually in the thermostat or in the heater core.

Anyways, there were some previous posts about acid-flushing a system. I can't seem to find any acid-based flush products at Autozone, Advance, O'Reilly, etc. Is an acid-flush something that a do-it-your-selfer can do? I've heard an acid-flush is primarly oxalic acid. Is there a name-brand acid flush product?

Any negative thoughts on acid flushing?

Overheating, runs poorly, sludge in the recovery tank, sounds like a combustion chamber to water jacket leak.
Are you getting any bubbles into the tank? Steam will condense before it gets to the tank unless you at a rolling boil.
Is there coolant in the oil (looks like dirty Mayo on the dip stick)?
Does the coolant in the recovery tank smell like gasoline after the engine has been running?
Answer yes to any one of these and it's a blown head gasket or worse cracked head or block, both of which have been a problem in the 4.3L.
Check your plugs, if one looks different, dirty, or clean that's probably the cylinder. Do a compression check and see if their all about the same, if not you got problems.
If that's your problem Bunkie, repost and we can talk.
Good luck
94

It's me again, I got so involved with the head gasket thing that I forgot to answer your question. Acid and aluminum don't mix, make sure whatever you use is aluminum safe or you may find coolant dripping on the ground or your carpets.
I recently had the irratic overheating and tried flushing the system, all I did was open a really big hole in the head gasket. The overheating was from an air block in the cooling system. Combustion gases leaking into the water jacket would collect and either block coolent flow or fill the water pump which is not designed to pump air.
The combustion gas will eventually find its way to the top of the radiator and into the recovery tank, which is why I asked did you have any bubbles there. I just got done with replacing the gaskets in my Olds Silhouette 3.4, fun the engine sits sideways under the dash. At least the 4.3 is pretty much out in the open.
If you haven't already done so get a good shop manual, I like the Haynes, I have the GM ($150) but I use the Haynes ($20).
See ya
94

Thanks, but I think I'm okay. It has never run poorly ... just overheated (irradically, inconsistently). I did check for bubbles in the reservoir today ... none that I can tell. There's no coolant in the oil (just did a recent oil change) and no oil in the coolant. The oil dipstick smells fine as does the coolant. Also, two cooling system pressure checks (one from dealer and one by myself) showed that it held pressure well. Wouldn't the pressure check reveal head gasket or intake manifold leak?

Anyhow, plugs, rotor, cap, wires are the next project in a week or so. I'll check the plug condition then. Not looking forward to the lower back pains caused by the distributer cap !!! haha



Overheating, runs poorly, sludge in the recovery tank, sounds like a combustion chamber to water jacket leak.
Are you getting any bubbles into the tank? Steam will condense before it gets to the tank unless you at a rolling boil.
Is there coolant in the oil (looks like dirty Mayo on the dip stick)?
Does the coolant in the recovery tank smell like gasoline after the engine has been running?
Answer yes to any one of these and it's a blown head gasket or worse cracked head or block, both of which have been a problem in the 4.3L.
Check your plugs, if one looks different, dirty, or clean that's probably the cylinder. Do a compression check and see if their all about the same, if not you got problems.
If that's your problem Bunkie, repost and we can talk.
Good luck
94

Thanks for the acid flush info.

With regards to "irradically", the word I think you meant to use is "erratically"