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Does the Coolant Seal work or Not?

Dear all,

My car is BMW2000 323i. My coolant is leaking, I need to refill it every month. The dealer told me I need to change the radiator and some related components in the coolant system. But the labor fee is too high.

I was told to use a coolant seal to fix the problem like K-Seal. After a long time searching on the Internet, I got confused. Someone says it works, but other people say it never works. What’s your opinion? What should I do?



Did the dealer show you the leak?

BMWs are expensive to maintain and repair! The dealer should at least been able to show you where the coolant was leaking out.

For minor leaks these sealant often work; if you have to add a significant amount each month, it probably won’t.

You need to get a second opinion from a radiator shop as to where and what is leaking. Sometimes it is a hose or other part. Years ago we had a radiator leak on our Nissan, the leak was on the engine side, thus not caused by flying debris. The dealer fixed it under warranty, but even then, in 1997, a Nissan radiator was over $400 plus labor of course. One from an auto parts store would have been about half that.

If you actually need a new radiator, go to a specialty shop, as an new BMW unit will likely set you back about $1000 just for the part.

I’m not an advocate of sealing additives for coolant leaks except to squeeze and extra 6 months out of a beater on its last legs. That’s not the case here.

I’m with Doc… someone needs to look at the cooling system and see exactly where the problems are. A dealer will always cost more… a BMW dealer a lot more. This does not require a BMW specialist, only a competent shop. BMW OEM parts are extremely expensive, but in the case of the cooling system you can get aftermarket parts just as good for far less. On top of that, dealer shop rates are typically much higher than independent shop rates.

A radiator shop is an excellent suggestion. Or, if you want to save long term, this is an opportunity to develop a relationship with a reputable independent.

OP: sometimes the sealant works too well and clogs up other things. Stay away from it and get it fixed properly, replace those parts which need replacing and don’t screw around with a leaky cooling system, you’ll overheat the engine and have a major bill on your hands. Rocketman

While I have used sealers many years ago and they worked well I would have to agree with @rocketman .The material can collect in the pin bores of thermostats and cause them to stick. Also, todays radiators have narrower passages which also would have a greater tendency to become clogged.

Take a tablespoon of ground black pepper and add it to the coolant.

I once had a Beretta with an external head gasket leak and adding the black pepper to the coolant stopped the leak for a year.

I keep a can of the stuff in the shop just for that purpose.


I will add another vote for not using sealer. I have seen too many cars where the sealer caused more problems, often times it was the result of adding more than instructed. Look for a second opinion, you may be able to find a radiator shop that can repair the radiator.

As others have said, find a good independent shop, get a non-BMW radiator. They’re $150 or so at Rockauto.

Seems as the expansion tank is a high failure item and easy to replace.


Replace the leaking radiator and whatever else is leaking

Stop leak MIGHT temporarily fix a very small pinhole in the radiator . . . or not

Stop leak will not fix a split o-ring or a crumbling intake gasket, causing coolant to pour into the crankcase

It appears your car is 14 years old. If the radiator is now leaking, just replace it. Like the others said, get an aftermarket part. is a good website for european auto parts. The parts are high quality, so they’re not dirt cheap

Or if you do want to be a cheapskate, buy a radiator from one of those small mom and pop radiator shops. They make their money in volume, so they usually have the lowest prices, often cheaper than any online vendor

If you go that route, just install it yourself

If you pay a shop to replace the radiator, let them supply the part. If you supply the part, they will not provide a warranty on the part, only the labor

If you decide to replace it yourself check to make sure there are no special fill procedures for the cooling system. Some cars require bleed screws to be opened or the use of a vacuum fill device. If proper procedures are not followed the cooling system can develop an air lock.

I’m not a fan of relegating a late model BMW to the get by with a crutch category.

My suggestion is fix it right even if it takes a spare time job held long enough to foot the bill and price the job around before committing to anything. A BMW dealer is not likely ever going to be cheap.

Another live for the moment option is to drop a few spoonfuls of ground black pepper or mustard seed into the cooling system.

Will that make it smell like an Italian car?
Sorry, I couldn’t resist. {:stuck_out_tongue:

Thank you guys.

I decide to replace the hose and radiator soon. And NEVER use coolant seal.


You might consider purchasing a radiator and hose from AutoZone or some other vendor. There are many online selling the same radiators and I would imagine a lifetime guarantee radiator from AZ is probably in the 100-125 dollars range.

I do not know who manufactures radiators for BMW but there’s at least a fair chance the same company that makes them for the local auto parts house also manufactures them for BMW.
Just like automotive batteries; a handful of companies produces dozens and dozens of brand names.