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Thread: Can running 110 octane race gas in a car not tuned for it cause head gasket failure?

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    Default Can running 110 octane race gas in a car not tuned for it cause head gasket failure?

    Hey guys, I'm looking at a BMW e36 M3 track car and the seller noted that the head gasket was replaced last year after failing when someone (not him) ran 110 octane race gas (probably leaded, too) in the car. He said a hole had burned through the gasket. I haven't seen the car in person yet but it sounds like it runs normally now. My question: is this the normal result of running very high octane fuel in a car that wasn't tuned for it? If so, what else could be damaged? It sounds like an odd failure.

    This car is a '95 and has the S50 motor. I'm curious as to the condition of the pistons and valve train. Of course, before I'd buy any used BMW, I'd have a PPI performed on the car by a reputable shop but this seems unusual and I'm hoping to tap into the vast braintrust that is TrackHQ for more insight before proceeding.

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    I should add that he normally runs 91 octane gas with the timing set for that.

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    No. It can kill the O2 sensors (specifically, the lead coats them and ruins them), but other than that it's impossible to cause engine damage by using race gas.
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    Thanks, Savington. That makes sense.

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    BMW Master bawareca's Avatar
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    Quote Originally Posted by Savington View Post
    ....... but other than that it's impossible to cause engine damage by using race gas.
    As much as you are correct,there may be some negative consequences from running this high octane.Higher octane burns a little slower,so it may be still too hot while the exhaust valve opens and the gasses exit the cylinder.That may lead to overheating of the exhaust valves(probably not in the street driving cycle,but very probable on the track) and lead to higher temperature in the combustion chamber and the head,causing more than normal head distortion.That combined with the probably original head gasket being 100k miles+ and 15 years + can easily cause head gasket failure.Could be just coincidence of course.

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    pretty sure that's not correct. Octane does not relate to the energy content of the fuel only the resistance to detonation. It doesn't burn any hotter. If it did it wouldn't be more ideal for boosted applications. Besides burning slower would be cooler not hotter right? Not that high octane fuel burns significantly slower than low octane. Again it's about detonation resistance.
    Last edited by krazik; 08-19-2013 at 08:22 AM.

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    Now you're left not knowing what cause the head gasket to fail. If it wasn't race fuel then what was the cause?

    Almost invariably, it's overheating, which leads to questioning the integrity of the head and whether it was merely removed and replaced or removed, machined then replaced.

    Compression and leak down tests are a must on that one.

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    Quote Originally Posted by krazik View Post
    pretty sure that's not correct. Octane does not relate to the energy content of the fuel only the resistance to detonation. It doesn't burn any hotter. If it did it wouldn't be more ideal for boosted applications. Besides burning slower would be cooler not hotter right? Not that high octane fuel burns significantly slower than low octane. Again it's about detonation resistance.
    It takes more energy/heat to ignite the higher octane fuel,correct?
    I didnt say higher octane burns hotter.The idea is that it is ignited later in the cycle and it is still very hot when exiting the cylinder.The effect is the same as retarding the timing with a lower octane.

    Quote Originally Posted by ucfbrett View Post
    Now you're left not knowing what cause the head gasket to fail. If it wasn't race fuel then what was the cause?

    Almost invariably, it's overheating, which leads to questioning the integrity of the head and whether it was merely removed and replaced or removed, machined then replaced.

    Compression and leak down tests are a must on that one.
    Main cause was pretty much overheating/age/mileage of the gasket.Race fuel may hepled a little or it may not.Those engines have very thin wall between the cylinders and tend to blow gaskets when they age,even without overheating.After a continious load(track session?) the head gets hot and fllexes a bit.Of course I didnt say this particular engine was not overheated.Also,compression and leakdown test wont say much about the condition of the head,except there is a huge problem.

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    Quote Originally Posted by bawareca View Post
    It takes more energy/heat to ignite the higher octane fuel,correct?
    I didnt say higher octane burns hotter.The idea is that it is ignited later in the cycle and it is still very hot when exiting the cylinder.The effect is the same as retarding the timing with a lower octane.
    From what I understand, this is exactly correct. I have no idea whether or not it had any relationship to the OP's question though.

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    It is a BMW. And a blown gasket. I wonder what it could be ?

    Dude: if it is a BMW, overheating is always caused by failed radiator, thermostat housing or water pump. BMW haven't been able to fix these issues for over 25 years. And probably won't.
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    Quote Originally Posted by bellwilliam View Post
    It is a BMW. And a blown gasket. I wonder what it could be ?

    Dude: if it is a BMW, overheating is always caused by failed radiator, thermostat housing or water pump. BMW haven't been able to fix these issues for over 25 years. And probably won't.
    True story. lol
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    Quote Originally Posted by bellwilliam View Post
    It is a BMW. And a blown gasket. I wonder what it could be ?

    Dude: if it is a BMW, overheating is always caused by failed radiator, thermostat housing or water pump. BMW haven't been able to fix these issues for over 25 years. And probably won't.
    New BMW don't have a coolant temperature gauge so they must never over heat.
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    Quote Originally Posted by Silversprint View Post
    New BMW don't have a coolant temperature gauge so they must never over heat.
    Even when the electric water pump fails...

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    Quote Originally Posted by suki101 View Post
    Even when the electric water pump fails...
    Even though it may sound stupid to you,the engine control unit knows the actual RPM of the pump and will let you know when it fails,and will reduce the power as well.
    The temp gauges of the BMWs since late 1990 are electronically stabilised and will stay in the middle between 140F and 240F,once it moves the engine is gone.There are many reasons for that,one is that the engine temp is controlled by the ECU,it may vary between 190F and 230F,for the efficiency's sake.On my E30 I can see the change if the temp goes 3-4 degrees.
    No matter of the bashing,BMW adressed the problems and all new models after E46 come with all aluminum radiators(I dont know any other brand so equipped).But the new models are expendable anyway...
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    whatever BMW did I am not sure. but 2 months ago, my brother's 335i engine overheated and took out the whole engine, bill was ~$9k. so clearly BMW hasn't fixed crap.

    Quote Originally Posted by bawareca View Post
    Even though it may sound stupid to you,the engine control unit knows the actual RPM of the pump and will let you know when it fails,and will reduce the power as well.
    The temp gauges of the BMWs since late 1990 are electronically stabilised and will stay in the middle between 140F and 240F,once it moves the engine is gone.There are many reasons for that,one is that the engine temp is controlled by the ECU,it may vary between 190F and 230F,for the efficiency's sake.On my E30 I can see the change if the temp goes 3-4 degrees.
    No matter of the bashing,BMW adressed the problems and all new models after E46 come with all aluminum radiators(I dont know any other brand so equipped).But the new models are expendable anyway...
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    Sorry to hear that.I am sure overheating happens to all kinds of cars,but for me the warning system is not good enough in BMW.Then again,they need to sell engines and stuff.

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    Hmmmm...lots of good info here. Thanks.

    He said the entire cooling system was replaced, too, but I'm not sure if it was before or after the head gasket failure.

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    ^^^ Mike -- all things being equal (which they are not), I'd look for another car . . .
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    Quote Originally Posted by bawareca View Post
    Even though it may sound stupid to you....
    I donít think itís stupid at all itís just disappointing the pump seems to built poorly; Iíve some fail within 35KÖ.and then thereís the costÖkind of funny though my co-worker drove around for a month with a bad pump and surprisingly didnít pop the head gasket.

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