Root cause of the Infamous Head Gasket Problems
12-13-21, 07:11 AM
#1
Driver School Candidate
Thread Starter
Root cause of the Infamous Head Gasket Problems
So in spite of the frequent head gasket discussions, I have been trying to find the root cause of the head gasket problem. My mechanic and I were talking about it and it was theorised that the head bolts could be the main cause.
I don’t think the bolts have sufficient tensile strength for this application. This could be why there is a slight separation between the head and block after so many heat cycles.
So I went online to look and the head bolts for my 2015 CT, 2015 Prius and 2016 Prius all have the same part number, HOWEVER they have all been replaced with an updated part number (possibly bolts rated at higher tensile strength). So it is possible Toyota was definitely aware of the head gasket problem and kept quiet.
But without access to a TSB or repair manual with updated cylinder head torque specifications, there’s no way to really confirm.
So my question to those of you that did have your head gaskets replaced, did you use the head bolts part number 90910-02166 or did you use the updated 90910-A2011? And if the updated, has the head gasket problem ever returned?
I don’t think the bolts have sufficient tensile strength for this application. This could be why there is a slight separation between the head and block after so many heat cycles.
So I went online to look and the head bolts for my 2015 CT, 2015 Prius and 2016 Prius all have the same part number, HOWEVER they have all been replaced with an updated part number (possibly bolts rated at higher tensile strength). So it is possible Toyota was definitely aware of the head gasket problem and kept quiet.
But without access to a TSB or repair manual with updated cylinder head torque specifications, there’s no way to really confirm.
So my question to those of you that did have your head gaskets replaced, did you use the head bolts part number 90910-02166 or did you use the updated 90910-A2011? And if the updated, has the head gasket problem ever returned?
12-20-21, 11:53 AM
#2
The cyclic operating nature of the hybrid 1.8 causes much more thermal expansion/contraction cycles than if it were running all the time...hence why these problems aren't seen on non-hybrid 1.8's. This loads and unloads the gasket more than normal. Couple that with a clogged EGR cooler, which leads to increased combustion chamber temperatures and there you have it.
That's not to say that new metallurgy on the bolts couldn't help. Last I read, torque sequence was 36 ft-lbs all around, then 90° all around, then 45° all around. I have not received any TSBs on alldatadiy related to heads/gasket/bolts (which is ridiculous...seems we know more about this problem than Toyota/Lexus do
)
That's not to say that new metallurgy on the bolts couldn't help. Last I read, torque sequence was 36 ft-lbs all around, then 90° all around, then 45° all around. I have not received any TSBs on alldatadiy related to heads/gasket/bolts (which is ridiculous...seems we know more about this problem than Toyota/Lexus do
)
Last edited by morganc; 12-20-21 at 12:12 PM.
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internalau (04-12-22)
12-23-21, 08:58 AM
#3
I think the consensus is somehow a clogged EGR system results in localized heating and overtime deteriorates the headgasket.
Localized heating (hot spots) is never good for any car, no matter how caused. Early 3/5 Series and E36 M3s had this issue with their M50/2 and S50/2 blocks in the back corners would result in a HG leak over time due to the back getting hot due to lack of coolant flow for whatever reason (maybe a passage back there is too small and gets clogged first over a long period of time I don't know) But little details like that can make or break (hah) a headgasket over time.
Long story short, keep your EGR circuits clean for best results!
Localized heating (hot spots) is never good for any car, no matter how caused. Early 3/5 Series and E36 M3s had this issue with their M50/2 and S50/2 blocks in the back corners would result in a HG leak over time due to the back getting hot due to lack of coolant flow for whatever reason (maybe a passage back there is too small and gets clogged first over a long period of time I don't know) But little details like that can make or break (hah) a headgasket over time.
Long story short, keep your EGR circuits clean for best results!
The following users liked this post:
internalau (04-12-22)
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