So, I posted here and ultimately decided the mechanic was lying to me. It turns out I was wrong.

Overheating at idle - mechanic says head gasket

The immediate overheating issue WAS due to the broken fan, but they uncovered a legitimate, tiny head gasket leak.

I've got coolant gases in my exhaust and a slight amount of wet exhaust from coolant getting in there. There is no current overheating problem, just a bit of coolant loss.

I have an independent mechanic who has done good work for me before who told me that my options were either to seal it up (he recommended K Seal), or to replace my head gasket. He said he'd charge about $600 labor (he works at about $25/hr out of his own garage).

Are there massive negatives with any type of head gasket sealer? The car is older, but I am going to keep it for many years, repairing it as I go (it's a sports car I intend to keep in running condition).

If I'm severely putting my car at risk, I'll just pay him. The only reason I'm considering this fix is the leak seems very, very small.

  • Grandad said "If its worth doing, its worth doing right" Do you intend to own the car for a long time ?
    – Criggie
    Commented Feb 27, 2017 at 3:55

2 Answers 2


If this is a car you are planning on keeping, I'd highly suggest just paying the money to get it fixed. A stop leak may work for a period of time, but it's only temporary.

A couple of things to consider with a stop leak is, it usually works great for keeping the coolant from flowing places it shouldn't, but it doesn't work too good at keeping the exhaust gasses out of the coolant. If the exhaust gasses are leaking into the coolant, you must consider it is getting injected into the coolant during the combustion process. Combustion pressures are pretty high, so having a stop leak on the coolant side of the equation won't do a whole lot to stop it. It may slow it down a little bit, but really, it won't be long until it's back at it again.

As stated, your best bet is to just get the work done, get it done right, and not worry about it again.

  • 2
    +1 since from the other thread, this is a Ford Mustang. If you just try to stop the leak, you take the risk that one day the leak will open wider, blow all your coolant onto the road, and the water temp gauge won't even have responded before you have a seized engine. (Personal experience: I once had a blown radiator that did exactly that to me. The first I knew there was a problem was when I took my foot off the gas and the engine seized, which locked the drive wheels solid and blew a tire before I slid to a stop. Don't go there!
    – alephzero
    Commented Feb 26, 2017 at 23:17
  • I'd be more worried about the coolant going the other way -- the leak opens up, the piston sucks a bunch of water in on the intake cycle, then the engine hydrolocks on the upstroke. Which is (probably) what happened to a buddy of mine -- his engine started running rough, blowing white smoke out the exhaust, then just stopped completely with a loud bang, he thought it was a backfire but found a mess of metal pieces in the oil pan that was from a broken connecting rod.
    – Johnny
    Commented Feb 27, 2017 at 0:11
  • @Johnny - With stop leak in the coolant system, it will stop the coolant from flowing that way. It won't, however, stop the combustion gasses from going into the cooling system (It will to an extent, but it's not going to work nearly as well). Commented Feb 27, 2017 at 0:35

Could be a good opportunity to get all the head valves, seals etc done at the same time - could be money well spent. However, I would regard any leak fix as a temporary solution - may last months or a couple of years... What is the car / engine as some engines are more temperamental especially sports car engines...

  • Yeah, the mechanic in question said he'd do the valve seals as well, just for the price of the parts because he'd already be stripping everything down. The engine is a V6 4.0L for a Ford Mustang. Commented Feb 27, 2017 at 4:45
  • 1
    @AndrewAlexander sounds like an opportunity to do a v8 swap...
    – Ben
    Commented Feb 27, 2017 at 11:55
  • @Ben, that's actually not a terrible idea. I'd obviously be paying a bit more of a premium, but I'd go from a high mileage V6 to a low mileage V8. I'll think about that if I can find a reasonably priced low mileage V8 engine. Commented Feb 27, 2017 at 23:59

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