Northstar Engines and System Technical Discussion Discussion, Head Bolts???? in Cadillac Engine Discussion; So now that I totally understand the reasoning behind the early North*s blowing head gaskets, I'm on to my next ...
- 03-02-04 06:28 AM #1Cadillac Owners Fanatic
- Automobile(s): 98 Concours 212,000 orginal motor,trans
- Join Date
- Jul 2003
- Springfield Mo
So now that I totally understand the reasoning behind the early North*s blowing head gaskets, I'm on to my next big question. Whats the deal with the head bolts on the later north*s that supposedly back themselves out or stretch in the head and cause the gasket to go also??? Thanks in advance!!!
- 03-02-04 09:32 AM #2
Re: Head Bolts????
I’ve never heard of any bolt stretch or backing out problem. The bolts work well within their strength range, the thread and under bolt head treatments keep them well sealed and tight (rotation wise).
The reason any of them have "bolt" problems is the aluminum block relaxing over time and effectively losing the clamping force on the heads.
The other big problem is failure to change the coolant on schedule, which can cause head gasket or block erosion, thus gasket failure.
- 03-02-04 12:58 PM #3
Re: Head Bolts????Originally Posted by fristim
No such thing happens.
If there is a problem with the threads in the block or something the head gasket can fail if the bolt tension relaxes due to the aluminum threads in the block yielding under repeated load of thermalcyclling...but that is very rare actually.
There were some cases of broken head bolts on the engines after 96 that were filled with the DexCool coolant IF the system was filled with straight DexCool....the acidic nature of the undiluted pure DexCool will cause a stress corrosion failure of the highly tensioned head bolts if the system is serviced and refilled with straight DexCool.
The head bolts have a preapplied loctite material on the threads and under the head bolt washer that acts as a high pressure lubricant for rundown and then locks the bolts so that they don't loosen.
You must be hearing about Honda engines that have trouble with the head bolts loosening causing "squeeking noises" from combustion pressure leaking. Seriously, THEY have THAT problem.