What Exactly Causes The 7M I6 BHG's ?

[suprageezer]

Okay I have been visiting this site for a while now and have read and experienced a zillion BHG's. Are there any True Engineers out there that can shed some light on exactly why this happens to this particular I6 engine? I see folk’s solution, complaints, raves, etc. I don’t think I have seen one post regarding the actual cause of this problem. I don’t mean, ya cause it's just the way it is. I and I am sure many others would like to get a really good engineering analysis of this issue. Who knows maybe some engineer having nothing to do with selling parts can solve the issue from a true engineering standpoint. I have wondered if the material the block is made from is incompatible with the material the head is made from in a heat transfer sort of sense. In other words is it possible the two metals heat transfer rates differ so widely that there is no way for both of the them to expand and contract at similar rates causing the gasket to shift between them until it leaks. Would true proper warm up before and after driving help this? Let's hear from some wizards and not just guesser's or sellers of the latest trend in head gaskets, because they ALL seem to have issues.

Rick

 

[MassSupra89]

Torque.
The headgasket was only torque'd to about 56lbs/in. from the factory. Where many say at least 75lbs/in. is needed.

 

[NDBoost]

lack of user knowledge

 

[supra90turbo]

Not to mention the use of a composite headgasket on a forced induction engine. That attributes to it somewhat. Toyota revised the headgasket after several failures, but never issued a TSB or Recall.

 

[madsupra88]

Detonation!!

 

[supra90turbo]

n00bism.

 

[madsupra88]

n00bism.

:rofl: that too

 

[drjonez]

Torque.
The headgasket was only torque'd to about 56lbs/in. from the factory. Where many say at least 75lbs/in. is needed.

lack of user knowledge

Detonation!!

all of those are SPOT on....tq it right, tune it right and you'll be fine.

 

[CTsupra]

:werd:

 

[cass10169]

I don't recall for sure if it was here, but I think I have seen someone mention waterjackets not being made correctly in the block causing to much heat. Though I could have just been dreaming this all up too.

 

[jdub]

I read an article on this subject by an engineer type...had to do with the differences in thermal expansion of an aluminum head and iron block. Basically the premise was the heat generated by the motor combined with the thermal expansion characteristics of the different metals caused the stock bolts to stretch. Especially at the rear of the motor where the down pipe routes with the 1st CAT on a stock pipe...this is where the heat is the greatest. Eventually the bolts loosen due to this...combined with the inadequate torque spec and the composite HG, you get the BHG we all know

Kinda made sense to me...most stock HG failures I've seen at at the #6 or #5 cylinders. On the other hand, I'm not an auto engineer...feel free to raise the BS flag :dunno:

 

[lagged]

well my first two were due to detonation. this one, i dont really know what caused it. it wasnt sudden either, there were signs early on that i ignored. so it was a slow progression and its just getting worse now..

 

[Ckanderson]

It's also due to people posting normal questions in the FAQ section... thats a PRIME cause of BHG

 

[IJ.]

Chicken and Egg scenario... which came first

In our motors we have cause and effect going on including many random factors that will cause a BHG.

Low Tq settings

Badly maintained

Any leak in the cooling system

No coolant used or incorrect concentration

Badly prepped surfaces

Bad tune

Faulty fuel system

Detonation

In the past I've ran 30 psi daily on a 4V Toyota V8 using a composite head gasket with no issues so I don't buy that being a reason for failure.

 

[mkIIIman089]

all of those are SPOT on....tq it right, tune it right and you'll be fine.

Agreed.

 

[SySt]

What causes the 7M's headgasket issues? Cast iron block vs a cast aluminum head, they expand at different rates. The length of the head plays a roll. It is also a turbocharged engine that tends to take more heat than most N/A vehicles which emphasizes the different metals and expansion rates. Lets also not forget that any gasket is a weak spot, period.

 

[Joel W.]

I figured someone would have mentioned the lack of spacing between the bores by now?

I think this has something to do with it also...

 

[IJ.]

Joel: The Siamesed bores add to the torsional ridgidity of the block so I don't see the bore spacing being that much of an issue.

An extra pair of headbolts around each bore would have been nice though!

 

[Yellow 13]

This thread should be 7MGTE BHG problems. The GE's headgaskets almost never blow.

 

[91T breezen']

This thread should be 7MGTE BHG problems. The GE's headgaskets almost never blow.

I blew a GE's hg! I modified the air intake, the car ran lean, + bad 87 gas, + 100 degree day, + detonation, Voila! BHG!:biglaugh: Car is a winter only driver now! JK! Down, awaiting motor swap(?)