LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Bad head gasket, intake manifold gasket, or both?

Old 04-20-2019, 12:01 PM
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Re: Bad head gasket, intake manifold gasket, or both?

Originally Posted by Injuneer View Post
Leaking head bolts are not the same as a leaking head gasket. Coolant pressure is 18 PSI. Combustion chamber pressure is way higher when the fuel ignites and burns. Can not compare a head bolt leak to a head gasket leak.

GM actually recommends stop-leak tablets for the LT1 with a fresh coolant change, but it isn’t to stop head gasket leaks. It's to stop low pressure leaks like the bolts. But I am not aware of anyone that actually uses the tablets. They use head bolt sealant. Stop-leak is not going to seal a head gasket leak. If the mechanic was afraid using head bolt sealant was going to affect the bolt torquing, all he had to do was install studs, using the sealant.

This thread is going exactly the same way the last one went, with the four misfiring rear cylinders. In the very first response, post #2, I suggested you check the fuel pressure. But you gave a jumbled answer indicating the mechanic had determined the pressure was low and bypassed the inline pump, and it was OK. You insisted on following the diagnosis and advice of your mechanic, and trying to develop theories explaining why the people who were trying to help you were wrong.

This went on for 20 more extremely lengthy posts, where you (or your mechanic) kept coming up with new theories about the problem, pretty much rejecting the advice you were given. Finally I told you that you had to get the car back and get your hands dirty. At that point I just stopped helping. Only then did the problem with the Aeromotive fuel pressure regulator come.to light. I see the same frustration developing above.
Thank you for the info provided in your first two paragraphs, that is the information I need. Logically, I want to be absolutely sure that the use of a liquid head gasket sealant is NOT advisable before I take the plunge and replace the head gasket(s). I can't know if I don't ask and/or do the research. Your answer tells me what I need to know. Thank you for that.

As far as your reference to my other thread, my very first post indicated that I was frustrated with the mechanic for waiting so long to check the fuel pressure. Information I gave was jumbled because it was coming from him and I was simply conveying what I was being told. Had I simply relied on him or believed everything he told me, I would have never posted for help here in the first place. If you read through the thread, I never even implied that anyone was "wrong". I simply asked questions and theorized about possibilities as logically as possible while the car was still captive at his shop anyway. From my first post in that thread the only thing he did was take 5 minutes to show me the noid light acting weird one day, other than that he never touched the car again.

I'm glad he didn't touch it again and that I decided to take it back, as he would have had me try new fuel pumps, a new PCM and new injectors; and would have never second guessed his botched fuel pressure test that should have revealed the bad AFPR. Unfortunately the damage had already been done with his "experiments" before I even posted the thread we're discussing, 98% of his "work" had already been done. I waited too long and put too much trust in him, because he HAD BEEN a very good mechanic overall for 17 years and was a trustworthy family man. Sometimes we put too much trust in people and get burned, it just happens.

Speaking of frustration, I find it very frustrating when I am just getting clarity on something I'm learning about and a key person knowledgeable / helpful decides to throw in the towel and/or gets negative. I don't understand the negativity. I'm just a lay person doing the best I can with limited knowledge, so I'm asking questions, just what is the harm in asking??? Give the simple guy here a little credit, I did ultimately diagnose and repair the AFPR-induced miss after all. When I decided to start over by checking fuel pressure and you decided to give me a second chance (thank you), even you stated that even though it was a good idea you didn't see why low pressure would cause a problem with the rear 4 cylinders. I made the observation that the vacuum line from the AFPR is attached to a port on the intake that is biased to the rear; and realized it could be flooding the rear four cylinders much worse than the front four. So without even running the engine I scrutinized the AFPR and took appropriate measures to verify that it was bad. Replaced it with a Borg Warner AFPR and finally the mysterious nightmare miss was resolved.

Was this such a bad outcome? Your efforts (and others') were not wasted and I appreciated the help. I am only trying to gather info and learn as much as I can here in this thread just as I did in the other one, sorry it appears to be going "exactly the same way". This "situation" with my car that I really only want to sell (but I want it right first) has become a tremendous burden for a long time and I just need help, that's all. If I didn't care about doing the right thing, I'd just put it up for sale and warm it up before someone comes to look at it (so it wouldn't smoke like it does at cold start) and play dumb. I could never do such a thing and I wouldn't use a liquid sealer in the radiator either if it isn't appropriate (yes, I'm clear that it isn't now, thank you).

It doesn't seem that diagnosing a bad head gasket is complicated (likely, I have already confirmed it with the smell of antifreeze in the oil filler cap and the other things I mentioned), I am just dotting i's and crossing t's before I travel to the car again. Sorry my posts are so frustrating for you, even when your help assists to create a positive outcome for me.

Originally Posted by 1995_LR View Post
Sealant on the head-bolts of an LT1 is mandatory, and the builder encouraged the use of stop-leak. I am starting to see where your problems began.

Your builder was a f-ing moron.
OooooK. As I said, I may be misquoting him from years ago. I opted to use sealant on the head bolts anyway. The built 355 has been in the car since 2005 with over 20K and no issues until late 2017 when the wonderful Aeromotive AFPR failed and a fumbling mechanic ran the engine way too much while "trying different things". This same mechanic "tried" to build this engine back in 2005 too, but he was stumped by an incorrectly ground custom cam (ground way off). I had to take it to MD for the brilliant man I spoke of to diagnose the issue and finish building the engine, which he kindly offered at no charge. I probably misquoted him, as he's no moron by any stretch of the imagination, I'll just leave it at that.

Last edited by canbaufo; 04-20-2019 at 12:03 PM.
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