If the cooling system or engine overheats an aluminum head or engine is toast and it only takes once. The iron parts will take the overheating long enough for you to correct the situation and usually no harm is done other than some coolant on the ground.

I remember the VEGA all-aluminum engines and their silicon nodule walls with all of the smoke following them down the road. You see the same thing with the aluminum lawnmower engines.

Aluminum expands more with temperature changes and this motion can destroy gasket sealing etc. Progress has been made but why chase problems and suffer other drawbacks when you already have a great durable material??? Automakers like aluminum because it is light and machines easily. The money they save comes out of our pockets later -big time.

 

Very true!!! What's interesting, the Vega all aluminum 4 cylinder was pure garbage (typical GM), while Mercedes used the same technology (in their all aluminum 3.8L V-8) and was fine!!

 

I think they had a better Vega engine later but by that time nobody wanted one. Mercedes usually does a better job on engineering but the same "HEAT==TOAST" problem still remains. There are a few things I look for in a vehicle and an iron engine is one of them. I have had my fill of aluminum failures. I don't think it is acceptable for a McD's wrapper to take out an engine.

 

I don't buy what you're selling, Torque. Look at all the ATV, motorcyle, chain saw, outboard, etc engines that are made of all aluminum. MILLIONS. Both 2 and 4 stroke, water or liquid cooled. Many ultra high performance engines are made from aluminum, and they have no reliability issues. Ford engines all have aluminum heads on them now. Would they do that if aluminum was inferior?

 

Is the result of the overheating due to the material the engine is made from, or is it due to the design of the valvetrain components, etc? The reason I ask is that I haven't heard of a lot of people having trouble with aftermarket aluminum heads on an american cast iron V8. I'm sure there are problems, but I've more often heard of people having problems on poorly designed foreign aluminum engines (most notably mitsubishi 3L V6, where if they run hot, the valve guides drop down in the head, due to a bad design, not simply because the engine ran a little hot). The weight savings from using aluminum over cast iron is substantial.

 

its not just the heat , but more of the weight it throughs around. imports and lawn mower have lighter connecting rods smaller bores. same with newer cars today, rods are thinner due to design change, but still are just as strong. if you have less weight to trough around there is less flex. flex a piece of aluminum and it stress fractures, flex a piece of steel it bends back into position, if not bent to much of course. as far as the expanding difference, head gaskets are not graphite any more, they are switching to MLS (multi-layer shim) gaskets. they are stronger, can take more abuse, transfer heat better, and can take more heat without failure.

 

I've never had an engine that would tolerate overheating. If it gets hot, it's gonna warp. Plain and simple.

 

You don't have to "buy it" but none of your examples have anything to do with an automotive engine. Driver's of ATV's etc can see that newspaper covering their engine. A car driver will sometimes miss the fact that they just inhaled a newspaper or McD's wrapper. Failure to do so should not cost an engine. Racing engines are a fine application of aluminum, -never said they weren't.

Check out the number of failures reported for aluminum production heads... Just read a little here.

Most of the applications where aftermarket aluminum heads are used on iron V8's are racing type applications where they are torn down frequently or special care is taken, -not daily drivers.

Iron engines will take a lot of abuse, of course if you ignore them completely they will warp too. Just not near as easy as aluminum.

I just told you guys what I have learned from my own experience. I have also learned from watching this board and reading years of engineering journals. I am not going to argue with you. Have fun with the aluminum junk if you want, just give me iron.

 

Again, I've never had an engine, iron or aluminum, that would hold up to overheating. Get one hot and you have problems. Also, one newspaper on your radiator won't make an aluminum engine go Kaboom!! If you get enough trash on your radiator to make your engine get hot, it will be ruined whether it's made of iron or aluminum. Get it hot and it will warp. It's really pretty simple. Aluminum engines are actually less susceptible to overheat because they conduct heat better, allowing for better disipation of heat through the metal itself.

 

Snag, -Talk to an automotive engineer.

 

what about all the toyota v8's - they are alloy as is the rover v8, most of the japanese stuff utalises aluminium heads - yeah they crack but so do cast iron heads - i'm running aluminium heads on my 302 and don't percieve there to be any problems as long as i don't overheat it - same as if i was using cast iron heads

 

Eric, are you an automotive engineer? (nothing to do with the discussion at hand, I was just curious, since that's what I'm studying to be)

 

You don't need to talk to an engineer to know that overheating an engine is BAD. Period. Regardless of materials. I have warped a few heads in my day. They were all iron on iron blocks. Got them hot and they warped. One blew immediatley, another blew a head gasket a few weeks later. Sure aluminum will also warp, but again, the problem is not with the material itself, it is with the overheating. If you think your iron block/heads are so tough, then just drain your radiator and start driving. See how far you get before it blows a head gasket because it will be warped. I'd bet it's less than 30 miles before it's locked up or blown.

 

No, I opted for mechanical, and have worked with automotive engineers on various projects. I usually do machine design and control work.

My point is that yes they will both overheat and warp but the aluminum parts are a LOT easier to damage. I have saved a lot of iron block engines as long as they still had some coolant in them.

Please ask some automotive head rebuiders what types of damage they see. Aluminum head rebuilders even have a special "overheat indicator" they install.

Just check the forums here re aluminum heads on some of these engines.

 

I can understand what you are saying, but I don't think it is as cut and dry as you are making it out to be. I will agree that it is easier to damage aluminum engine components, but I don't think that they are inferior simply because they are aluminum. I'm a junior in mechanical engineering here at NC State, and also do a lot of design on the FSAE race car we design and build each year. I'm co-team leader of the engine team, and have helped tear down and rebuild the little honda F4i motorcycle engine we use as a powerplant. The cylinder bores are aluminum, and the 6000 mile motor we just acquired is showing signs of cylinder ovalization already. The older F2's and F3's used a cast iron cylinder liner and seemed to not wear as quickly. No problems with the cases either, even when used as a stressed member of the car's chassis. We've also had some cooling problems last year, with water temps getting up in the 240-250 degree range, and saw nothing wrong when we tore down the motor, other than the cylinder walls showing a little wear and ovalization.