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Coolant flush problem

I have a 2001 Honda Civic with 145000 miles. My mechanic recently completed a coolant flush on my vehicle and when I went to pick it up said that the radiator sealant was affected by the flush so I should bring the car back in a week to have them check it. On my way home the engine was steaming and continued to that week. When I brought the car back they said it looks like its sealing again but I may need to buy a new radiator soon. The engine still occasionally has steam coming off of it and another mechanic says I need a new radiator ASAP. I don’t know much about cars (obviously) so I am wondering if this is a normal occurrence? Is this something I should pay for if the mechanic damaged the sealant when they completed the flush? Thank you

This radiator probably has a plastic top section, which eventually cracks.
After 12 years it’s about that time. And fiddling with the hoses etc. for the flush can start a crack.
If so expect the leak to quickly get much worse.
In the future I recommend against chemical flushes. Just drain and refill the coolant on time.
Change the radiator cap and thermostat too.

When a coolant flush is performed, it can remove some of the stop-leak product that’s added at the factory.

Manufacturers build vehicles by the thousands. So they install radiators supplied by vendors by the thousands. Out of the thousands of radiators that are installed not every one is going to be perfect and not leak. So instead of replacing a radiator after a vehicle comes off the assembly line they add a stop-leak product to avoid that problem.

Here’s the stop-leak product that most vehicle manufacturers use on the assembly line.


Your radiator has an aluminum core with plastic top and bottom tanks. There are rubber seals between the aluminum and the plastic. At twelve years old, it would not be uncommon for the rubber to start leaking. The cheapest alternative is to replace the radiator.

You do NOT want this engine to overheat, they do not tolerate overheating very well.

As for your mechanic, the term flush means a lot of different things. Did he use a chemical to flush the radiator? Did he use a flush machine? Did he just drain the radiator and block and stick a garden hose in the top of the radiator and flush it that way?

Personally, unless the cooling system is in real bad shape, I prefer to not do any type of flush on a radiator at all, just drain and refill. a reasonably well maintained cooling system should never need a flush. A drain and refill every 5 years or so is enough.


Was this the first coolant service your car has ever had?

I had to replace the radiator on my early 90’s Corolla when it sprung a leak a couple years ago. Not a big deal. The replacement radiator cost $90 is all, took me a couple of hours to replace, a relatively easy job. No AC, and manual xmission, so that made it easier for my case. I think you should just bite the bullet and replace it so it doesn’t become an expensive issue later. I think Honda recommends only that Honda coolant be used in Honda cars, so don’t use aftermarket coolant. Buy your new coolant from a Honda dealer.

I agree with @George. It’s not that unusual. The point is, don’t wait. Fix it ASAP. Even a consistent but slight loss of coolant that may go unnoticed can lead to a something worse, like a blown head gasket. It doesn’t take a catostrophic loss…just lower then usual coolant level over time can do itn some older motors. Also, when fixed, as recomended, do the coolant service, by the numbers…use Honda recomended and service intervals.

You don’t need Honda coolant. I have a Honda and I used dexcool on its first service, been using a universal long life coolant ever since.

These links provide a pretty good tutorial on the subtleties of replacing engine coolant.

Thank you everyone for your advice. @keith, I don’t know exactly what they did for the flush but I think they mentioned a machine. @db4690 this was the first coolant service the car has ever had. I will get this fixed ASAP.

If this is the first cooling service, then I suspect that you may have a potentially much larger problem. This engine has a timing belt that has a 7 year 105k mile interval for service. The water pump is usually replaced with the belt and when the water pump is replaced, so is the coolant.

You need to find out if the timing belt service has been performed, and if it has not, you need to have it done immediately, preferably at a Honda dealer. A broken belt will trash this engine. Honda dealers usually have a package deal for the belt service that many independents can’t beat, and teh Honda can be a bit tricky compared to other cars.

I do all my vehicle maintenance my self, including timing belts, except the timing belt on a Honda, for that, it goes to the dealer.

@keith, I did the timing belt right around the 7 year mark but I was not aware of what else was done with that. I can look through my records, but do you still think I have a larger problem if I already completed that service?
Thanks agian.

No, the potential larger problem was the timing belt, but you did have this done. If it was done at a Honda dealership, they probably did the water pump so this would not be your first coolant service. If you had it done at an independent mechanic, then you would have to check.

I am just not big on doing any kind of flush except for brakes (when new pads are installed) and toilets.

If you have not had the transmission serviced regularly, you should have the ATF drained and refilled. Honda even recommends against flushing of the AT even though I have seen some Honda dealers try to sell that service. For the AT, use only Honda ATF. I use generic fluids for most everything else, but on transmissions, I only use the manufacturers ATF and on Honda’s, only use Honda power steering fluid in the PS system.

BTW, have you noticed any measurable loss of coolant? The steam could have come from some spillage when the radiator was filled up. You can also get some occasional steam from condensation on a cold morning. You need to check the coolant level both at the overflow tank and at the radiator cap, when the engine is cold.

You should do this frequently until you determine if there is any loss of coolant or not. If not, then I would not worry about it. What is critical is that you do not allow the engine to overheat so keep an eye on that gauge.