Most Likely Failure Mode on 4.0
#1
Most Likely Failure Mode on 4.0
I have discovered what I believe to be the biggest weakness in the 4.0. My cylinder head machinist explained it to me and it's not a cracked heads or block.
The scenerio goes like this, a problem in the cooling system causes the engine to overheat. The block is cast iron and the head is aluminum. They have different expansion rates which causes the head gasket to compress more than normal when in a hotter state. The engine cools off and leaves a gap between the head and block. Water rushes down the cylinders and causes catastrophic failure. Water gets in the oil in large quantities and its all over. Moral of the story, keep the cooling system in tip top shape or kiss your engine good-bye. This is what happened to mine according to my machinist who has done hundreds of these. I am looking for a better head gasket to minimize this effect. I think thicker is better to take up some of the expansion and cool down. That's the main problem with these engines IMHO. I am convinced that's what caused mine to fail because everything else inside the motor looks good because I got it quickly after the water intruded.
Phil Swanson
The scenerio goes like this, a problem in the cooling system causes the engine to overheat. The block is cast iron and the head is aluminum. They have different expansion rates which causes the head gasket to compress more than normal when in a hotter state. The engine cools off and leaves a gap between the head and block. Water rushes down the cylinders and causes catastrophic failure. Water gets in the oil in large quantities and its all over. Moral of the story, keep the cooling system in tip top shape or kiss your engine good-bye. This is what happened to mine according to my machinist who has done hundreds of these. I am looking for a better head gasket to minimize this effect. I think thicker is better to take up some of the expansion and cool down. That's the main problem with these engines IMHO. I am convinced that's what caused mine to fail because everything else inside the motor looks good because I got it quickly after the water intruded.
Phil Swanson
Last edited by philipswanson; 04-23-2016 at 04:02 PM.
#5
all i can say is no kidding, overheating an engine causes damage, doesnt matter if it has aluminum heads or not. water will not "rush" into the cylinders. however if the head becomes warped from overheating it will start to consume coolant due to a leaking head gasket. this concern is non unique to 4.0l engines. simple solution is, make sure you dont drive the engine without coolant, the temp gauge is your friend
#6
all i can say is no kidding, overheating an engine causes damage, doesnt matter if it has aluminum heads or not. water will not "rush" into the cylinders. however if the head becomes warped from overheating it will start to consume coolant due to a leaking head gasket. this concern is non unique to 4.0l engines. simple solution is, make sure you dont drive the engine without coolant, the temp gauge is your friend
Phil Swanson
#7
if you overheat a sbc with cast heads, you can take out a head gasket as well, the point is, if you are overheating ANY engine you are already doing damage, the aluminum head cast iron block combination has been around for many years, and works very well, as long as some idiot doesnt keep driving it while overheating and cook the engine.
#10
Yes, any engine can be damaged by high heat but they have different weak points. Yes the cast iron block and aluminum head combination has been around a long time but they don't all have this problem of compressing the head gasket. Again, the Ford SOHC 4.0 is especially prone to head gasket compression. Apparently, more so than many other engines of similar materials used in their construction. I know the 3.8 and the 4.6 seldom have head gasket compression.
I am just passing along information from our head machinist who again has done hundreds of these and thousands of other heads and knows more about head problems than any of us. You can sluff it off or take it seriously and learn something. Your choice.
I am just passing along information from our head machinist who again has done hundreds of these and thousands of other heads and knows more about head problems than any of us. You can sluff it off or take it seriously and learn something. Your choice.