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Overheating Sentra Head Gasket Sealant

2004 Sentra, 100K, rough starting, running good. Dealer diagnosed Head Gasket leak, #3 cyl. misfire. $!300+ est. No can do.
I added K&W Head Gasket&Block Sealant, per instructions. Filled radiator and reservoir with 50/50 coolant.
Car start improved but CAR NOW OVERHEATS after 15 min. driving. Blasting heat brings guage to normal zone.
DID SEALANT CLOG SYSTEM? How doI diagnose? What to check next?

Hard to say, but its a good chance the radiator is partially blocked… Will it over heat at idle or just while driving it?? Are your cooling fans turning on??

How often was that coolant system serviced over the life of the car? If it had been neglected & had corrosion & build up in it, then there’s a good chance the radiator is now clogged. That’s what those liquid head gasket sealers are designed to do - clog up little passages in the cooling system. The stuff isn’t “smart” enough to be picky about what it clogs. So if you start with a contaminated system, there’s a good chance you will clog some things up that are supposed to be open.

Its also quite possible that it clogged up some of the head leak, but not all of it. The next time the car is up to temperature, look in your coolant overflow tank. Any bubbles? (Only do this if its not a pressurized tank).

Replace radiator and thermostat…Then have a couple of independent shops give you an estimate on replacing the head gasket…

I don’t believe in chemical crutches that are used to repair a head gasket problem. They may work on a leak that does not breach the combustion chamber but once combustion pressures are applied I just don’t see it holding at all.

Now you not only have to get the head gasket fixed, you will most likely need a radiator and thermostat. And get all the K&W Head Gasket&Block Sealant flushed out of the system before it plugs up something else.