Hybrid Vehicles and Head Gasket Failure

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7,600
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It sounds a lot like the 7M-G(T)E head gasket issue that afflicted the 3rd gen Supra and 4th gen Cressida(also known as the Mark II in Japan) - but people suspected a combination of graphite head gasket and undertorqued bolts to blame for the issue - the fix if a BHG hasn't happened was to retorque the head bolts. The Japanese switched over to MLS head gaskets for that reason alone - better sealing but they are still using a fluoropolymer and graphite/moly coating while Fel-Pro on their "problem solver" PermaTorquePlus MLS head gaskets are using a different coating that supposedly holds up to rougher surface finishes and the aftermarket environment better. The 3rd and 4th gen Prius also have cooled EGR not unlike a EPA2004/2010 diesel engine - the EGR cooler is a smaller scale version of what is used on bigger engines but if the EGR cooler causes BHGs on Toyota hybrids, wouldn't they issue a service campaign with an improved part or modify VVT-i operation to provide more of a pseudo-EGR effect? Older Toyota engines with VVT didn't have EGR systems - retarding the intake valves a tiny bit during the start of the intake stroke provided the effect of EGR.
 
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17,298
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OH
An interesting theory that may not hold up to scrutiny. First off, this wouldn't only be a problem with hybrids but with every vehicle with a stop/start implementation as well. Also, if you have a vehicle with a real temperature gauge, you'll notice that engine temperature is far from constant and will vary considerably with load. It's not unusual to drive some miles to the first traffic light in cold conditions and to then watch coolant temperature decline while idling on the red light. Also, while a hybrid will spend maybe 15% of its miles in EV mode, how much temperature is really lost while the gas engine is briefly silent? Not so sure that this is anything more than a known problem with one generation of Prius engine, with occasional failures spread across other models as well as makes.
 
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18,283
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Silicon Valley
I think these days 150K head gasket problem is really barely "good enough" we are not in the 80s anymore. Our standard is around 200K these days for "reliable" and 300K for "very reliable". 150K means it is a throw away car and barely good enough, less than that would be considered junk.
 
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Western S.C.
Originally Posted by PandaBear
I think these days 150K head gasket problem is really barely "good enough" we are not in the 80s anymore. Our standard is around 200K these days for "reliable" and 300K for "very reliable". 150K means it is a throw away car and barely good enough, less than that would be considered junk.
I mostly agree, except that all your numbers are too low. The two 80s cars with which I was best acquainted both went well beyond 300k without head gasket trouble. Under 200k is ridiculous.
 
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