Head Gaskets questions

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Okay so my car started to overheat and the mechanic said it had a blown head gasket bbut the previous owner said it needs a new thermostat so i replace the thermostat and the car seems to be runnin okay for now(touch wood)

My question is

When a head gasket is blown

1. Does the car emit black fumes?
2. Does a car start with a blown head gaskets

Thanks & good night

posted by  Stack Bundles

"Black fumes" are an indication of an improper air-to-fuel ratio, i.e. that the fuel mixture is too rich. This can be caused by any number of problems, but it's a safe bet that a "blown" head gasket is not one of them. There are two -- and only two -- conditions that result in a rich mixture. Either there is too much fuel being introduced or there is not enough air being inducted. While these two statements may at first seem to be two different ways of saying the same thing, I worded it the way I did to make it easier to understand the conditions. In modern engines, fuel quantity is controlled by the on-board engine control computer. Any condition that allows more fuel to enter the combustion process than the amount that the computer thinks is entering will result in black smoke from the "too much fuel" condition. Similarly, any condition that allows less air to be inducted than the volume that the computer thinks is present will also result in black smoke, but now it is from the "not enough air" condition. Among the many possible causes of black smoke would be excessive fuel pressure, leaky injectors, failed idle air control, failed air flow sensor, and air induction leaks downstream of the air flow sensor. Note that these are just some of the possibilities...

As to your second question, it all depends upon the engine design (type) and how (or where) the head gasket is "blown". A "blown" gasket is one that is no longer sealing as it was intended to do. In the case of a head gasket, there are generally four areas of sealing in which the gasket is involved -- compression, coolant, lubricating oil pressure, and lubricating oil return. Leaks are possible from any one of these to one or more of the others or to the atmosphere. The specific location and extent of the leak will determine the symptoms present. For example, if there is a leak from compression to coolant, it will be evidenced by extreme pressurization of the cooling system while cranking, and it may be evidenced by coolant steam in the exhaust and/or by coolant in the crankcase on a cold engine. A compression leak between two cylinders is likely to prevent a four cylinder engine from starting, but is far less likely to do so with a eight cylinder model.

posted by  cpprioli

I appreciate you answering the question But i dont understand it lol

posted by  Stack Bundles

I have a 1990 Daytona, (I have owned for 6 months now) amongst other issues I have been told this car has blown the head gasket 4 times!! (or course 2 months after purchase :ohcrap: ) From my understanding the cooling system can be the cause of this sometimes? And there were some issues with the car; I have replaced fan motor, relay switch and a broken wire, thermostat, flushed system...I think I have corrected all heating/coolant issues now and have heat and no more overheating...my question is, is it safe to assume the gasket may go again? Or is there another cause??
Thanks to all!

posted by  Fastrac

There's a few things you need to consider here, not the least why it happened in the first place. Unless its a super/turbo charged car chances are the initial cause was loss of water.

The problem you may be faced with is that if the head has not been properly checked and machined the gasket may continue to rupture. Worse still if the head has been overheated and it hasn't had any warp correction.

One of the most overlooked defects is although the head has been crack tested and lapped true, if the head material is an aluminium alloy it may well have annealed and thus will not hold the required tension. Sure a cylinder head machine shop should test this, but some don't or are told by the previous owner just to machine it flat regardless and it's put back on with stretched bolts to boot.

You should probably grab a torque wrench and see if the bolt tension is to spec or have someone do it it for you.

posted by  Wally

A lot of people don't have a clue what your'e talking about.

posted by  lectroid

This may be very true, but it certainly not a reason not to answer the question as Wally did! If a reader is unsure of how, for example, a head bolt can be stretched, or how bolt tension is to be checked, all it takes is posting a question to get the answer.

posted by  cpprioli

WELL,Do it,cobber. :thumbs:

posted by  lectroid

I appreciate your reply and thanks.....will check the bolt tension. From previous experience with a Laser, I have a fairly good understanding of the aluminium head cracking and what should be done to correct it....and I agree some owners just want the 'quick & cheap" fix .

posted by  Fastrac

No probs. As cpprioli posted if you don't understand just ask.

Something I'm sure CarExpert will agree with is that with OHC alloy heads a warped head can mean the cam tunnels are put out of alignment. So skimming or lapping the head contact surface may not work for long as the tension of the camshaft(s) start trying to twist the head back true ... and the next thing you have is either a cracked head and/or failed gasket again.

posted by  Wally

Thanks again Wally....and no worries, if I'm uncertain I will ask....I do have another question for you, as I'm honestly not sure here....my brother has an Eagle Talon (turbo)...he was told they do not make heads for these motors anymore??...so final quote to rebuild is $1950.00CAN ...now as I mentioned before with my laser I bought a used head and had it rebuilt...paid a total of $350 for rebuild (+ cost of head)....now I knew the mechanic quite well...so maybe I got a great deal...but is rebuilding the Talon head that expensive???

posted by  Fastrac

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