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Is flushing the coolant system necessary?

59K views 37 replies 19 participants last post by  Melon 
#1 ·
I believe I am WAY behind on replacing my coolant (it's been 105,000 miles since the last time). Not sure how I overlooked this, as I'm usually on top of things, but it is what it is now.

So, my question is, does Honda recommend flushing a cooling system, or just run distilled water through it and drain a few times until it comes out clear? I'm talking about something like Prestone radiator flush and cleaner.

Also, I came across "burping" the coolant system to get the air out. I have a pretty good understanding of how to do it, but I'm curious what happens if there is air left in the system.

Thanks,

Andy
 
#2 ·
It usually is 5 yrs. until the first coolant change then every 3 yrs. after that. Look @ your coolant, if it looks dirty then I would change it. Use of a cleaner is up to you, it will clean out more of the rust & any sludge but make sure you flush well. You can flush with the distilled water or some use city water for the flush, then follow with distilled water for the final flush just don't use well water as it may contain higher levels of minerals. Honda brand (dealer) or ZEREX Asian (NAPA stores or Amazon), etc., coolant has to be a P-HOAT formula & silicate / borate free. One member uses Walmart brand but I have never seen it @ my Walmarts. Coolant is good for 160K. If this is for your 04 I would get a new OEM radiator cap.
 
#3 ·
Just drain the radiator and refill. If "Honda blue" coolant is already in there, that's what I'd refill with. Maybe it's $25 at the dealer but since it's done every 5 years according to the jug, then it's not so bad and it has an unlimited shelf life. It is also pre-mixed with water. 1.3 gallons needed to refill the radiator.

Get one of these to burp the air out.
 
#11 ·
Why would the funnel be necessary? All you have to do to get the air out is run the engine with the radiator cap loose, right? I'm all for having special tools, to make a job easier, but I want to see the advantage before actually buying one. I remember seeing ericthecarguy recommend the funnel too, so I'm interested in exactly what the advantage is.
 
#4 ·
Have never done a flush on my accord because the coolant has always been crystal clear. I would only do it if your coolant is excessively dirty. Took 5 flushes(3 with prestone cleaner) to get the coolant clear on the 90 miata I bought.
 
#5 ·
I assume this is a 4 cylinder, so I do not know when the last time the water pump was changed but if it has been over 150,000 to 200,000 I would change it now with the coolant. I would not do a chemical flush but just a flush with a hose, while the water pump is off. In my opinion using distilled water to flush is a bit overkill. Also, insisting on Honda coolant is a fine but not necessary if you are flushing the whole system (be sure to get the heater core). If you have a air bubble the engine will not circulate coolant properly and may overheat. The easiest way is to fill the system with coolant, start the engine turn the heat on full and let it idle while making sure to add coolant to the radiator while the engine is running. Wait for the cooling fans to come on at least 3 times and make sure to add coolant when the fans run as the level drops. Fill the overflow bottle to the full mark and put the radiator cap on. Then check in the morning and fill the overflow bottle back to full and you should be done.

Sent from my Nexus 5X using Tapatalk
 
#6 ·
With such high miles, I'd skip any chemicals and do a flush with 4-5 jugs of distilled water. A jug of DI water is only a dollar and change so don't use a garden hose and risk corroding the system. If you go this route, don't add premixed coolant (like Honda Blue or Zerex Asian). Otherwise, you won't be close to a 50-50 mix in the end due to the water remaining in the block. Pep Boys sells Rechochem concentrate, which is an Asian-spec coolant.

This is also a good time to replace the radiator cap since it probably doesn't hold 1.1 atm of pressure like it used to.
 
#21 ·
With such high miles, I'd skip any chemicals and do a flush with 4-5 jugs of distilled water. A jug of DI water is only a dollar and change so don't use a garden hose and risk corroding the system. If you go this route, don't add premixed coolant (like Honda Blue or Zerex Asian). Otherwise, you won't be close to a 50-50 mix in the end due to the water remaining in the block. Pep Boys sells Rechochem concentrate, which is an Asian-spec coolant.
I agree with you here, but wouldn't using concentrate lead to the same kind of inaccuracy? I supposed you could mix the coolant a bit stronger to compensate for the water remaining in the system. I don't have the dilution values in front of me, but perhaps it's better to have a stronger dilution than a weaker one.

The reason I ask is because my car has not had the coolant changed as far as I know, and after 10 years it very well may be due. The stuff in currently in the system is green. It could be the original Honda stuff, or it could be universal. For peace of mind I would like to do a flush with distilled water before filling with new Honda blue. But that introduces the very problem you mentioned.
 
#7 ·
There is no need to do any chemical flush or run a garden hose through it unless the system is contaminated or you've put in the wrong type of coolant in the past. When I changed the coolant on my v6 at 208k miles, it was very clean. The only dirty anything I found was inside the coolant overflow tank. Make sure you take that out and flush out the dirt / deposits inside.

Consider changing the thermostat, only $25 OEM and comes with gasket. Since the entire system would be empty anyway after draining.

Burping the cooling system just means running the car with the radiator cap off to let air bubbles escape. You'll see some coolant get sucked down once air is evacuated, then top off to the neck of the radiator and close the cap that's it. No special tool needed, just a funnel.
 
#8 ·
I've used Prestone in the last billion years. Everything's fine. You can hose it if you want to. Most likely you'll be fine just by draining and refilling. Try to drain the block as well, as there's some coolant in it too. I see too many posts about coolant changes but very few, if ever, drain the block.

I'll quote "brwnflsh" here:

It may not be in the owner's manual, but it is in the service manual. The block drain is on the rear side of the engine, toward the passenger side. There is a nipple coming out from inside the nut, so you can fit a drain hose on it, then loosen the nut. A good bit of coolant will come out. A box-end wrench is the best way, because you need to have the hose attached to the nipple.
There is a procedure for doing the coolant change, which includes turning the heater up full hot (before draining), and starting the engine with the radiator cap on loosely (after filling), then running the engine until the fans come on at least twice. It's not as simple as drain and refill. Good luck
 
#9 ·
If you are not the original owner and don't know the coolant history, run some Prestone radiator flush through it with tap water. Rinse it out by flushing with distilled water. Keep heat full hot during entire process to open up heater core. To burp, run engine with front end on ramps and radiator cap off, till the fans turn on. Again, heat turned to hot.

The Honda blue is of course, excellent. I use Walmart Supertech concentrate, mixed with a gallon of distilled water. To mix, simply pour a gallon of each into a bucket and stir. I used to use Prestone, but they stopped making it silicate free years ago. I have a thread somewhere, comparing Supertech's ingredients with the Honda stuff. It is the exact same formulation, cept' for the color.
 
#10 ·
My coolant has been changed so many times, between regular maintenance, the time I got a free radiator because someone hit my car, changing the front motor mount (which required me to remove the lower rad hose), my coolant is good to go. Still going to change it with Honda blue in another 25K.
 
#12 ·
Tightening new thermostat

I plan on flushing my coolant system next week (it's been over 100,000 miles) and will be replacing the hoses and thermostat at that time. The specs call for the thermostat housing to be torqued to 86 INCH pounds. I have't seen many good reviews on torque wrenches that operate in inch pounds. Would I be ok just using blue loctite and making the bolts snug?
 
#13 ·
86 inch pounds is 7 foot pounds, that is not very tight at all. I would recommend just snugging it with a 1/4" ratchet.

If you had a foot-long wrench, it would only take 7 pounds of force to get it to spec. Really not much at all, don't overdo it.
 
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#14 ·
If you will be doing this on your 04, if it is the 4 cyl, be careful working around the sensor wires. The wire can break in the plug, they are no longer available to buy, only the different wires for the V6 are available. It will be off to the salvage yard.
 
#15 ·
Snug it with a 1/4" ratcheting wrench on the two 10mm bolts. I did not torque these at all. Snugging it means hand tight, tight, then a little more over the tight, then stop right there or you'll strip or break off the bolt.

The only very accurate low torque rating torque wrench is Snap-On as I've found out recently. I bought one off ebay for $129, used.
 
#17 ·
LOL... sorry my friend, but you just made an argument for this being a total waste of money. Maybe for a mechanic, but for the DIY guy? You'd end up using it every five years. You can actually leave the car running and do one top off at the end.
 
#18 ·
I've burped all my cars by jacking up the front end (parking on a sloped driveway also works) and revving the engine to 2000 RPMs or so several times until the cooling fans cycle on/off twice. During this time, the rad cap is off, heater set all the way to hot, and blower off. From basic science, air likes to rise to the top. The Lisle funnel has its place too; probably makes filling the rad less messy. I just never had a need for it.
 
#19 ·
You don't need a funnel for any fluids, that's why people frequently see spill spots in the engine bay haha. Just aim and pour very accurately and you'll be fine :)

eric the car guy is referring to the Lisle spill free radiator funnel set which has a special cap that adapts to a funnel that allows you to pre-pour a load of coolant while burping. I never see why that thing is necessary. I just use a regular funnel. With that fancy gadget, you pre-pour a ton of coolant, but only some gets sucked down, you end up having to suck the extra back out with a turkey baster and dispose of it before you can close the OEM radiator cap. When I burped the system last time, I might have put in a tiny 1~3 oz only to top off.
 
#20 ·
Thanks for the tip on the sensor wire. Where exactly is that located?


Thanks to all who replied. I was thinking just snugging it without a torque wrench would probably suffice. I'll be using blue loctite and check it after a day or two to make sure the bolts are all snug still.
 
#22 ·
Blue coolant or green coolant, with today's formulas it really does not matter. The key is the percentage of ethylene glycol to water. You want to be at at least 50% up to 70%. A cheap coolant tester can verify that, 50/50 gives you freeze protection to -38f and boilover protection to 225f. Increasing the percentage of ethylene glycol to 70% lowers freezing protection to about -58f and raises boiling temperature to 240f. Going to higher concentrations of ethylene glycol raises the freezing point BUT also raises the boiling point. The sweet spot is 65/35%.

100% ethylene glycol boils at about 380f and freezes at 8f and also can only transfer about 65% of the heat that 100% water can. So it is all a balancing act, 50/50 works for most everyone.

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#24 ·
So, my question is, does Honda recommend flushing a cooling system
No, Honda doesn't. I apologize if someone already answered this. The Honda Owner's Manual only calls for the coolant to be replaced. There is nothing indicating it should be flushed. And the procedure for replacing the fluid in the Honda Service Manual is nothing more than a simple drain and fill along with leaving the cap on loosely to burp it.

Now don't misunderstand me. :) I'm not saying people shouldn't flush! And I'm not saying how people should flush! It's up to the owner.
 
#26 ·
I know it's overkill but I just change all the liquids like the coolant, brake fluid, steering wheel fluid, and the V-Tech fluid every year. No need to flush, question whether to flush or this or that. Doesn't hurt and it's not that costly.
 
#33 ·
Hello, this is my first post, although I have been a lurker here on this great site for years. I own a 2007 I4 EX-L, purchased new. My question is not related to flushing, but simply the interval for changing the coolant.

According to the link below, it says to change the coolant at 120k miles. I'm at 60k right now, and the car's maintenance minder should tell me, according to the manual. Is it ok for me to wait for 120k miles, or is there a time interval that overrides the miles? I love the car, but the owner's manual can lack specifics, at times. Thanks for any advice.

" Replace engine coolant, then replace every 60,000 mi/96,000 km/5 yrs."
http://www.driveaccord.net/forums/1...59-03-05-maintenance-schedule-i-4-engine.html
 
#34 ·
The coolant has been in there 10 yrs. (at your mileage it will be 20 yrs. before the first change). I would change it to be on the safe side. Does it look dirty ? As some of us know changing (the auto. transmission fluid early), before the recommened 120K mile intervel has its advantages. Welcome to DA.
 
#36 ·
While you do want to test your coolant with a hydrometer, as qman posted above, you also want to use some test strips to measure the acidity of the coolant to see if your corrision inhibitors have deteriorted. You may want to have the rad. cap pressure tested or just replace with an OEM one.
 
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