What causes a head gasket to fail?
 

I have spent hours reading about people discussing the failure of their head gasket but it seems no one is talking about what causes these failure. What practices do we do to ensure engine longevity? I know there are a lot of basic engine building principals, but I am looking for a discussion about what causes a head gasket failure and how to avoid them.

Please, discuss.

Can detonation cause a failure?

What to look for when fixing a bad HG?

How to avoid a bad HG?

How hot typically causes HG failure?

Usually it's due to overheating of the engine causing either warping of the head or damage to the HG itself or both.

Symptoms include loss of antifreeze, sweet smell from exhaust, bubbles at radiator neck when idling, and in really bad cases vapor lock from one of the cylinders filling with coolant.

My favorite method for finding a bad HG is a hydrocarbon sniffer placed in the radiator neck while idling. It's pretty fool proof and available from most autoparts stores. Pressure testing is another method, but the coolant will bleed into the cylinder of where the HG has let go and if you don't catch it you may vapor lock the engine and do a lot more damage to the lower end.
You can also do a leak down test and see if you can get the coolant to bubble out of the radiator neck.

If you experience a blown HG due to an overheat, it's a good idea to have the head checked for straightness by an engine shop. Our block is Iron and unlikely to warp/crack unless you are just really awesome.

Heat warp is the #1 reason.

But I also had one fail on my wife's Tracker. Shop said head wasn't torqued down correctly, and loosened over time, causing a leak. Technically, it wasn't the gasket's fault, but it meant pulling the head and a new gasket.

I like this thread because I bought a 2000 1.8 engine that "has a blown head gasket". What should I have checked before simply putting just gaskets in this motor and throwing it in my car?

You could try just throwing a headgasket in there, maybe with a light coat of copper spray.
Most likely you will need to get the head milled flat though.

There are lots of ways of blowing a head gasket, but I agree the most common way its going to happen on a stock car is from overheating.

Toss the head on the granite kitchen counter and see if it wobbles?

Or use a straight edge and feeler gauge like a proper human being.

As for the question, what everyone said, though I have seen more "lifted" heads than I expected, the most recent 2 being a big boost evo and big boost supra. Both ended up with milled heads, new mls gasket, and ARP studs to replace the stretched stockers

Well, if it wasn't clear I was more interested in forced induction engines.

I agree with 18psi, even a non precise straight edge will be better than a wobble test.

Thirdgen, you really should look at the cylinder bore walls for scoring and or a wear ridge. Since you don't know and of the history of the car you should have the head checked for cracks when you have it at the machine shop getting at least the minimum resurfacing.

FTB, I did a shit ton load of reading about this recently and one of the top BMW engine builders who have lots of great write ups, addressed MLS head gaskets. They specifically said to NOT use copper spray. That the MLS HG has a wax coating that should be applied to a very flat and very clean surface. So from now on my heads will almost always get resurfaced. That said, one of the better machine shops in my area (Nascar country), the owner reused his MLS HG many times over, he said he just sprays it down with a good even coat of copper. He also said he would not do that on a street car, that he only expects his engine to run a couple hours between tear downs.

the cooling system.

Who uses MLS headgaskets? That shit is gross fail aids.

I sure hope that is sarcasm or I am lost.....I thought everyone on here was using MLS head gaskets?

Nevermind, I was thinking of fiber headgaskets. Those have aids. MLS is propper.

I wouldnt put copper spray on an MLS gasket normally, but when it comes to trying to ghetto fix a blown gasket I would try it. I know people who have done it.

Like I said before, I would plan on taking it to a machine shop.

answered your questions.

Okay. Thank you Brain!
I thought track guys were seeing 230+ without problems?
I believe my SuperMiata water pump failed causing me to run warm and thus I will be removing my head and having it resurfaced.

GMB water pupmps off ebay are what I have been using since 2005 and have yet to see one fail. I have probably put 25+ on various miata's running up and down the east coast.

I have a hard time believing water pump failure too. IF it really did, I'll be very surprised.

It had about 5K miles on it and was making a knocking sound. I also had intermittent flow through the heater core. I had the heat on and part of the time the I had really hot air and other times I had cool air, I would have thought thermostat except the water pump was making a horrible knocking sound. I don't know what else it could have been? When I changed the water pump I removed the thermostat but I fear the damage was done since it still ran warm, then got hot, and then I suspect it blew....I hope the HG blew because I have low compression on 1&4......I will know more when I get the head off in two weeks.......

yikes.

Sounds like air in the system. Probably nothing wrong with the WP (it can't pump air).

Note that one of the things a HG can cause is a pressurized cooling system (pressurized by engine/combustion pressure) that blows all your coolant out the overflow. At that point, you end up with a half-filled cooling system. Not good.

yea...we do see oil temps that high.