I'm planning on flushing the cooling system on my '92 Accord. I have a can of radiator flush. Questions:
1. In addition to initially opening the radiator drain and allowing the coolant to flow out, instructions say if the vehicle is equipped with an engine block drain, to open that drain and allow the engine block to completely drain as well. I definitely want to completely drain all the old coolant from the system including the engine block, and be sure the flush chemical circulates throughout the block in addition to radiator itself. Although I've yet to take a good look, apparently on my engine the drain plug bolt for the block coolant is located either behind the exhaust manifold or right close by the oil filter. If by the oil filter where it is reasonably accessible I will probably not have much problem, but I think if it's located behind the exhaust manifold that accessibility will present a problem, and in that case I really don't want to have to undertake some kind of extreme measure just to be able to get a wrench on it for removal/reinstallation. Is there a practical alternate method of thoroughly draining the engine block of all the old coolant, or is removing the block coolant plug the most reliable or best way to go if I can? Does disconnecting the lower hose from the radiator serve to drain the engine block the same as removing the engine block coolant plug? I do plan on removing the thermostat during the time I have the engine running with the radiator flush stuff in so I don't need to wait around and wonder if/when the thermostat is open/closed. With the thermostat removed does that help to ensure if I do remove the lower radiator hose from the radiator that all engine coolant will drain from the block, or not make a difference?

2. Instructions also say to let the engine idle with the radiator flush inside for at least 10 minutes, but “time and weather permitting” to “run the vehicle” for 3-6 hours with the radiator flush and water solution in the cooling system, which, it says, will provide a deeper clean and help to restore the cooling system to top efficiency. Should it typically be necessary to have to run the vehicle for 3-6 hours as suggested with the flush chemical stuff? And if so, would just idling in the driveway be okay, or should the 3-6 hours of “running” the vehicle be like on the road at driving speeds?

Any comments appreciated!

 

Make sure the heater control is set to full-HOT so you don't have coolant trapped in the heater core.

There's 2 plug/bolts on the back side of the engine block in the neighborhood of the oil filter. I'm tempted to say the larger one is antifreeze, but I'm not real confident of that. The lower hose connects to the thermostat, which is not the lowest point.

I had a 1998 & I opened the wrong one. I saw oil seeping around the threads when it was half-way out, so I just tightened it back up & opened the other one.

Still there was a bunch of coolant that still didn't drain. So you will want to do multiple fill/drain rinses with clear water to remove ALL of the flush chemical.

I think as long as the engine gets warm enough to open the thermostat, then the flush will circulate everywhere. I think the only benefit to actually driving is just to get the engine hot enough to open the T-stat. You can do that by putting a blanket over the grille.

 

This is from the owner's manual.

 

So it's necessary even if I remove the coolant block plug, because that's still not the lowest point, to be sure to do multiple fill/drain rinses, right? Hmm, I wonder then just how much lower the actual lowest point is?

I'm also just thinking of temporarily removing the thermostat just during the time the flush chemical is in the system to not have to worry about waiting around wondering for sure if when/if it's open and I'm getting full system circulation. Even if that seems unnecessary, not anything wrong with doing that is there?

Thanks

 

Very helpful, thanks redbull!

 

I'm thinking that coolant plug in the block is the lowest point.

 

Even tho it's the same architecture (F-series), the 1998 might be different...

Even using the block drain, I still had to fill/drain about 4 or 5 times (with T-stat removed) before the color was completely gone. I never removed/rebuilt that engine, so I never had a good look inside the block. I was kinda disappointed the drain wasn't REALLY a good complete drain.

I normally remove the T-stat so I can fill & run for a minute then drain. That way each fill/drain cycle doesn't require an actual warm-up. I wouldn't DRIVE that way because the T-stat has some control over flow distribution even when it's open.

 

Me, I know where you are going, so I'd pull the t-stat and be sure it seals back off without a stat in there - might have to get a new gasket, use the old one to try to seal it without stat and the new one when you put it back.

I'd also pull/clean/empty the overflow. On the 5th gens it comes out pretty easy, I'd pull it, empty it and then clean it with water and that as best you can. Then for the flush I'd have water in it. After the flush, empty and wash it out again - this should get rid of any small amounts of the flush.

BTW - I sent a PM and an e-mail. Let me know

 

Thanks for that additional info JimBlake.

 

Thanks poorman212 for that advice too. Will do. Got yer PM will be gettin back to ya very shortly.