Greetings all. I just finished working on my mom's '99 Accord V6's cooling system. The radiator blew the other day. The car has ~140,000 miles on it, and I'm pretty sure this was the original Denso radiator. I suppose that's not too bad. Anyway, I realize that the right thing to do is to drain the coolant from the block, especially since the coolant looked like basic green Prestone, but Honda has the thickest part of the axle half-shaft at about the same level as the plug, making it very difficult to loosen. Plus, having dealt with block drain plugs before, I realize that it could also make for a bigger job if threads get messed up, etc,. or it doesn't seal well.
I made myself a wrench that would work, despite the clearance issues, but the wrench was really flexing and I didn't want to cause myself extra grief. FWIW, I used a the box end of a 14mm combination wrench on the bold and a 1/2" breaker bar set into the open end. It fit pretty snugly, but it was too high of a pucker-factor as I pushed on it, so I left it alone.
I used some flush in the system and followed up with 3 or 4 distilled water flushes but there was still color in the solution. And since it took a little over a gallon of 50/50, the system still had 1.7 qts of mostly pure water. So my 50/50 was probably diluted down to 40/60. My mom doesn't go anywhere that this would give problems for freezing, but it does get hot. What I may end up doing is draining some coolant in a few weeks and add pure concentrated OEM blue to it in order to bring up the ratio.
Either that, if the car needs a half-shaft, I'll work on getting that block drain plug out and put in a new solution. Not the end of the world, but the location of the plug made it very difficult to do it the exact right way.
So, anyone replacing the passenger half-shaft on a similar year V6 should think about a coolant change at the same time. Cheers.

Oh, and unfortunately I diluted the full gallong of concentrated OEM blue slicate free last night. Otherwise I would have had the higher concentrate to add. Murph...

 

I tried to remove the block drain bolt on a 95 accord and had a similar experience to you. I ended up just doing radiator drains and refills every 2 years with the green stuff and never had an issue. You can go with the route of adding concentrate to match what water is in the block after a flush. You may want to use a coolant tester to see the lowest temperature your coolant mix will protect your engine.

 

Thanks, PAhonda.

FWIW, I did read somewhere that some use Loctite red on that drain bolt, and that you pretty much have to heat the bolt with a torch to loosen its grip. But there again the axle CV boot is so close to the bolt that I'd be very afraid of melting the rubber.

Out of the many cars I've owned or worked on in my life, probably only one had the block drain bolt in an accessible place. And IIRC, that ended up being a bad thing. I was able to remove it relatively easily, but not get it re-sealed with the same ease. Oh that Murphy sure loves cars. Cheers.

 

If the block plug is that difficult, I'd leave it in so it doesn't turn into a real big job like you said.

 

Agreed.