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Chemical reaction with aluminum heads... blown headgasket

Discussion in 'The Garage' started by dirtwarrior17, Mar 12, 2005.

  1. dirtwarrior17

    dirtwarrior17 Banned

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    I've heard aluminum heads on a cast iron block will cause a chemical reaction from the head gasket when the motor gets hot. I don't know if its just the ford mustangs in a certain year range but my moms stang blew both head gaskets and warped the aluminum heads when it did it. The mechanic that did her swap said the aluminum heads on the iron block caused a chemical reaction out of her head gaskets and caused them to blow because the motor got up to 260.

    I've had my old stock motor (iron heads) up to 300 with no blown head gaskets.

    anybody know if this is true?
     
  2. sled_dog

    sled_dog 1 ton status

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    Aluminum and steel together with your cooling fluid create a sort of electrical thing. I've heard of it being corrosive but never harmful like you are describing. There are hundreds of production vehicles using this configuration and lots of race ones too. Sounds to me like a thermostat went or something else and the tech is just talking out his butt. When the car gets that hot, woman most of all, usually keep driving and it blows head gaskets, cracks heads/blocks, and in the case of aluminum is more likely to warp heads. It happens on steel head/block combos too. If you ran at 300 for an extended period of time, wouldn't surprise me if you warped or cracked a head somewhere and just don't know it.
     
  3. dirtwarrior17

    dirtwarrior17 Banned

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    yeah i still don't know why the hell her gaskets took a dump... i was with her when it started to spike and made her pull over at a napa and i changed the thermostat myself... we continued on and it got hot and just gave up.

    As for my old stock motor... it is sitting on a jet ski stand at my uncles house. I had it up to 300 for about 1 min while driving because i couldn't find a place to pull over. A month later I spun a main. I think it had something to do with both getting smokin hot and the fact my tranny tv cable wasn't set right and was shifting so damn hard even with no throttle that in second gear it would "screech" my 35's. Although the motor didn't run like it was hot... could have been a bad temp sensor. hope i don't find out the hard way with my new motor.
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I really depends on the cylinder head construction, as well as the material used. It's difficult to make generalizations with anything. If we're talking about factory aluminum heads, they may be cast as light as possible and wouldn't be able to stay rigid as easily as a thicker/beefier cast.

    FWIW, sometimes head gaskets go and there doesn't seem to be any reason. My friend has a GMC with a 4.3...head gaskets are gone again. Fourth time now.

    Each time he's had them checked for flatness, I think they got milled once because they were slightly warped. He is a very careful and thorough shadetree mechanic, runs Autometer guages and the truck has never overheated.

    I do know the Ford 3.8's are famous for puking head gaskets, is that what was in the Mustang?

    Rene
     
  5. sled_dog

    sled_dog 1 ton status

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    I'm guilty of running hot when I know I shouldn't. Heck I lost an intake gasket on the way to NYC(was too far to turn back) and had to drive around for a few days and just fill the rad every time I stopped.
     
  6. Fierospeeder

    Fierospeeder Banned

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    besides the flatness, the block and head have to have the proper finish, so the gasket doesn't tear when they expand or contract. There is a special tool to be able to tell the finish quality.
     
  7. dirtwarrior17

    dirtwarrior17 Banned

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    bingo... I even did some research on em because i was planning on doing the work but my mom wanted to have it done by a mechanic because she "needs her car as soon as possible". Spent 15 minutes on the internet and found out these things give up at 70,000 miles like clockwork. There were boatloads of people who had this same thing happen at 70-80k miles... my moms was at 76k.

    Seems like a recall should be in order.
     
  8. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I had a Mecury Sable with the 3.8...:doah: The irony was that the tranny worked great. I didn't feel like wasting most of a weekend and 'K5' money to fix the head gaskets though. Sent it to the crusher...

    Rene
     
  9. dirtwarrior17

    dirtwarrior17 Banned

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    almost forgot... after she paid 2k for her heads, labor, etc. she had a rod bearing go(another 3k for a rebuilt motor)... now she has 1k less into it than she paid for it.
     
  10. Thunder

    Thunder 3/4 ton status

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    Probabally the most common major repair in engines with alulminum heads and a cast iron block is head gaskets. If you have that combo, You can usually figgure on replaceing them sometime after 60K.
    Thats really why I dont like to put aluminium heads on trucks. Dont see any real power gains unless running high compression ratio. And blowing a head gasket is a problem that is always lurking .
     
  11. AkMudr

    AkMudr 1/2 ton status

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    I'd rather run a good valve job maybe some port and polishing and some decently sized valves on a cast head than go aluminum, yeh you can get some good power with alum. but the trade off sucks as far as the gasket goes. With a lil more $$ you can turn some hp with cast heads. Plus the chances of warping ahead are alot less.
     
  12. sled_dog

    sled_dog 1 ton status

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    Actually if you do some research the only real advantages to aluminum heads are, lower octane with higher compression and lighter weight. Side by side, same setups, a steel headed motor will make more power.
     
  13. jarheadk5

    jarheadk5 1/2 ton status

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    While it's true that aluminum heads on an iron block sets up a good scenario for galvanic corrosion (also known as dissimilar-metal corrosion) of the heads, I think the bigger problem is the different thermal expansion characteristics of the aluminum and iron. The head(s) expand at a lower temp, and at a faster rate, than the block. This creates relative motion at the gasket surfaces, and even though we're only talking about a few thousandths of an inch, it's enough to tear a crappy gasket apart over time.
    When I did the head gasket on my Eclipse (at 80K - NA 2.0L with iron block & aluminum head) due to a bad oil leak, the old composition-type gasket left far more of itself on the block surfaces than the head, and what was on the head came off pretty easily. The new OEM gasket was a MLS-type (Multi-Layer Shim) with a couple steel leaves sandwiched between two plastic-feeling layers. 32K later, and not a leak from the head.
     
  14. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Ok, since i'm an automotive machinist and do lots of Dealer work here locally i can answer some questions for you. Let me start by saying that the Ford 3.8 V/6 is notorius for blowing head gaskets as you've found out for yourself. I will tell you the reason that was given to me by the Ford factory representatives, (wheather or not it's the real reason i don't know).

    Ford says that the head gasket blowing on the 3.8 V/6 was due to an incorrect torque value setting on the jig that torques all the head bolts on that engine from the factory.

    I have cleaned and tested and resurfaced about 5 sets of those heads a day, 5 days a week for almost 6 years back about 1994 or so. Very rarely was a head cracked but they were always warped about .006". Ford did have a recall on those engines for head gasket failure when i was doing all that work for them here locally. The gaskets usually blew anywhere from 70K-90k miles. Ford used a different style head gasket and also new head bolts to cure this problem.

    Anyhow, i just thought i would chime in with some experience on this subject. I almost forgot to mention about the aluminum heads and iron block situation, the term that i think someone was trying to say is that if you have this situation and don't keep the proper amount of coolant in the cooling system you will have electrolysis. Electrolysis is the chemical reaction that happens when you have two dissimilar metals with electrical charges being passed within and not having the proper solution to withstand the corrosion. This is part of what antifreeze helps to protect.

    Having aluminum heads and cast iron blocks has nothing to do with head gasket failures. Almost every car that is made today is built with this set-up. The head gasket required for use of aluminum heads on iron blocks is made of a little different material so that the head gasket will not brinnel the aluminum head.

    Also a profilometer is what is used to determine the roughness of a surface.

    Ok, that is my .02 for the day. :thumb:
     
  15. Fierospeeder

    Fierospeeder Banned

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    Yup, thats what those watchmacallits are called.

    you mean metal artist? I find some of the stuff you guys do is amazing. It is more then what a typical machinist does because you have to fix a lot of strange things.
     
  16. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    :bow: :bow: :bow:

    Rene
     
  17. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Whew, thanks Rene. Glad i pulled that one off. :rotfl:

    Actually, i have quite a bit of info stored in my head and when i can add my .02 to a thread that i think might help others or is a good piece of info i don't mind sharing it at all. I'll bet most people have never even heard of a profilometer before. Another word for a slightly different type is a comparator which you can get from Fel-Pro gasket company pretty cheap. They do come in handy sometimes when a certain surface roughness needs to be checked or "compared" to another object. :thumb:
     
  18. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    We use a comparator when finish quality is critical at work. Well, in the machine shop they do...everything I deal with still has mill scale on it. :laugh:

    Good see to accurate, quality info posted, especially when it's on topic. :)

    Rene
     
  19. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I would just like to add the type of head gaskets to the discussion typically recommended for this application.

    They're called, "MLS" gaskets, for Multiple Layer Steel. Basically they're steel head gaskets with some sort of rubber or something between them. The seperate layers allow one layer to move with the cylinder head and the other to move with the block. This allows for good, solid sealing without the different rates of expansion/contraction destroying the gaskets over the long run.

    For MANY head gasket failure-prone vehicles, these gaskets are the cure. :grin:

    Just your Fel-Pro certified Counterpro Timmay talking in this thread. :grin: :grin: :grin:
     
  20. mouse

    mouse 1/2 ton status

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    I've used MLS gaskets in this application on a couple of occasions and have never had any problems. Definitely the way to go.
     

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