Aluminum Heads

[Old smart]

I am in a fortunate position in that my local independent repair shop owner has “smart” experience through his other shop in Europe. He is presently dealing with a coolant issue with my Subaru H-6’s all-aluminum engine, and passes the following advice on to any aluminum engine owner (450 and 451 owners). Aluminum cylinder heads have considerable expansion and contraction as they heat and cool, placing a lot of strain on the head studs (stretching) and causing the head nuts to “seat” into the soft metal, essentially loosening the head when cold. The result is coolant leakage until the engine warms up - in my case causing a “Check Engine” fault by one of the oxygen sensors. The advice is to have the head stud torque settings checked and re-set (in the proper order!) at some reasonable interval before head gasket blow-by becomes an issue. The all-aluminum Cadillac Northstar V8s are so afflicted with the problem that adding “stop-leak” to the coolant is a routine maintenance procedure.

[SmartBob]

Roger that. My Neon blew a head gasket just after the warranty was expired. Fortunatley I stopped before the head warped. Apparently a routine problem with the DOHC 2. The engine was discontinued after another year or two.

[Karl Roth]

a lot of what you describe is an alu head on iron block issue the motor we are getting is all aluminum and should not have those issues.
karl

[Old smart]

Originally Posted by Karl Roth

a lot of what you describe is an alu head on iron block issue the motor we are getting is all aluminum and should not have those issues.
karl

The head itself will expand and contract relative to the steel head studs whether the block is iron or aluminum. It is true that the aluminum block will also expand and contract, but that puts no strain on the head studs unless, like some motorcycle engines, the studs go all the way through the cylinder barrel and into the crankcase.

[Karl Roth]

Originally Posted by fishrdnc

The head itself will expand and contract relative to the steel head studs whether the block is iron or aluminum. It is true that the aluminum block will also expand and contract, but that puts no strain on the head studs unless, like some motorcycle engines, the studs go all the way through the cylinder barrel and into the crankcase.

You are correct, I truly hope that this machine will run as well and as long as I hope. Had a 2 litre BMW 6 years ago with an iron block and aluminum head. Keeping her running meant trips to the junk yards Army didn't pay as well then. lots of warped heads there all the time. this on a four year old car. My son drove down from Boston to take me to Hartford CT to the Smart dealer and combined on the trips saw 5 flat tires more than I have seen in five years. Thanks for the thoughtful input to the forums.
karl

[oldbike]

My 30 years experience as a technician point to two causes of head gasket failure on aluminum-headed engines, OTHER than the few that were defective designs from the factory.
Those two causes have been:
Failure to monitor PH level of the coolant that resulted in corrosion failure of the gaskets or
Improper operation of the cooling system/ chronic overheating (thermostat failure, cooling fan failure, blocked air flow etc.) resulting in loss of cylinder head gasket tension.
Modern gasket technology makes allowances for the differential expansion rates of the material used in engines
Of course, this is just my own opinion

[Karl Roth]

oldbike that international pickup a driver, think the smart will be just fine with the recommended service look forward to driving it.
karl

[Fredvon4]

oldbike

I will add that one other failure mode often gets overlooked by repain or rebuilders... proper assembly and re-torquing cyl head bolts and exhaust manifold bolts/nuts is more critical on aluminum motors

A lot of new engine manufactures now do this extra step on the engine assy lines...they actually run in the motor on a test stand and do the re-torques later when cold soak has happened...

[oldbike]

Originally Posted by Karl Roth

oldbike that international pickup a driver, think the smart will be just fine with the recommended service look forward to driving it.
karl

Of course the IH is my driver. The smart is just for cargo weight to soften the ride!

[buds302]

if all your saying is true. how is then a honda motor from the 80s that is all aluminum still runs to the day with no head gasket failure? our 88 honda civic was bought new from the dealer by us. it has 400000 miles. its had i dont know how many oil changes and coolant changes along the way. the only serious maintenence that weve done is change the waterpump and timing belt. the waterpump wasnt even required. but since i was changing the timing belt anyway. it drives the pump so it is good nature to change it as well. ive owned 5 other hondas as well and none of them have had any head gasket problems. ive got a 2002 civic in the driveway thats turbocharged. it has 240HP on a stock 4 cylinder. if anything it should be having head gsket problems. but no it doesnt.

like already said. the biggest problem with aluminum engines is people dont change the coolant often enough and it corrodes the motor. ive seen it. ive had it happen to me. ive gotten parts that were corroded. go to any junkyard an pull apart an aluminum engine that has been sitting in there for a few years. you will notice the corrosion.