Why 3.8 Head Gaskets Leak - TCCoA Forums
 
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post #1 of 10 (permalink) Old 01-01-2015, 11:03 AM Thread Starter
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Why 3.8 Head Gaskets Leak

So is there a definitive answer to why the head gaskets leak on the 3.8? I've heard a few theories over the years.

Improper torque? Seems like one could pull the valve covers and re-torque before leaks occur...
Poor gasket materials?
Temperature-related flexing of iron block and aluminum head?
Bad design? Too little material between cylinder and water jacket?

Once the head gaskets are replaced, do they last longer than the originals? Or is it just a matter of time...

And is there any difference in the failure rate on SC units? I see different torque specs given for the head bolts.

1996 Thunderbird LX (4.6), previous daily driver

1995 Mustang GT (5.0), daily driver
1995 GMC C2500 (5.7), alternate daily driver

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post #2 of 10 (permalink) Old 01-01-2015, 11:25 AM
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Probably a combination of everything you mentioned. The gaskets were improved in 96 and then again on the 99.

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post #3 of 10 (permalink) Old 01-01-2015, 02:58 PM
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The head's deck thickness and the gasket materials are the biggest contributors. It's perfectly possible to build an iron/aluminum engine where headgasket problems are practically unheard of(like the 4.6), the Essex 3.8, I suspect, may have been intended to be all iron from the start like the similar Buick V6(the V6 Ford arguably copied from) and then rushed into adding lightness before production by making everything they could around the iron block aluminum and didn't change any of the tooling and specifications to do so. The 96+ changes largely addressed the problem.

SCs are probably a bit worse but every pre-96 3.8 will pop them eventually, it's kind of like the plastic intakes on the 96/7 4.6s. Generally speaking the best solution on those is to get the head and block surfaces machined smoother for MLS head gaskets and use studs rather than TTY bolts.

stock bolts being TTY by the way pretty much make the notion of retorquing a feeble effort at best. Not to mention that the engines are 20 years old and probably already popped at some point or the damage is already done.

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post #4 of 10 (permalink) Old 01-09-2015, 01:48 PM
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On this same topic...

I'm going to look at a 96 Cougar today that has bad HGs. Upon researching the parts to get it fixed, I noticed that the gasket and bolts have a different part number for each year 94/95, 96 and 97. The 97 version is the MLS gasket, where as the 96 is a graphite type. I'm curious how much better is the 96 in comparison to the 94/95?

1994 Thunderbird - 2000 4.2L M5R2 now has 55k

1995 Thunderbird - 2002 Alum 4.6L SVO - Awaiting transplant... (Parts donor)

1996 Cougar - 2004 3.9L 4R70W
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post #5 of 10 (permalink) Old 01-09-2015, 05:59 PM
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SC are no worse than any other 3.8. What causes them to pop IMO is detention issues (made worse by driver either running wrong fuel, lack of maintenance or too much boost/modding). SC gaskets are equivalent to 96+ gaskets.

Pre 96 is/was a design issue.

If all else fails get a bigger hammer!

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post #6 of 10 (permalink) Old 01-09-2015, 09:42 PM
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Quote:
Originally Posted by bowez View Post
made worse by driver either running wrong fuel, lack of maintenance or too much boost/modding
Yes but I'd wager every last SC built has been subject to two of those three abuses in the last 20 years

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post #7 of 10 (permalink) Old 01-09-2015, 11:34 PM
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Most of the "head gasket" failures I have seen were the result of an overheated engine, warped head .. not necessarily the gasket itself.

The 89-93 SC heads actually have a thicker deck than the 94/95, not sure on failure rates between the two because there were many more of the prior ones built.

The last 3.8L NA I had a blown actual gasket on was ruptured from the coolant port into the combustion chamber, probably a combination of heat, time, maintenance. It was a customers car that actually didn't display any symptoms, the not changing the oil was what ended up seizing the camshaft, broken timing chain, bent valves ..

I did a 4.6 with a blown head gasket, it was blown out externally from the side of the block, most likely too much heat / oil leaking, oh and it was a Range rover.

Coolant changes is one of the most overlooked maintenance items, used up corrosion inhibitors, electrolysis.

And the term is Detonation or pre-ignition .. not detention.
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post #8 of 10 (permalink) Old 01-10-2015, 05:52 AM
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Oops, just realized what I spelled. Thansk

But by what Dave Dalke (XR7Dave) says all SCs experience detonation, I think Ford knew this too since they came with knock sensors.

Though I do have to say none of the 3.8s I've killed were HGs, one bearing failure and the other was dropped valve (very spectacular).


Just implying SCs fail from abuse and pre96 fail from design and others fail from lack of maintenance--by in large.

If all else fails get a bigger hammer!

93 SC Tbird
MPII w/ Plenum,90mm MAF, 85mm TB, 40# Injectors, 255 lph FP, Double IC w/fan, SCT Chip (Tuned by Jerry),3/4" Raised Top, F52-TT TC, SilverFox AOD 550, SPT-R VB
96 1/2 XR7 Sold and Salvaged
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post #9 of 10 (permalink) Old 01-10-2015, 07:45 AM
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The 3.8L wasn't a bad motor, i have owned one, and i overheated it...95 degree day and the upper coolant line (the one going to the V on the block) burst on me. 1992 Mercury Sable, i didn't catch it since it never shot the temp gauge up, parked it at my destination...horrible odor...rod knock.

If it is FWD, the engine has a cramped engine bay to be in, if it is a minivan it is both cramped with horrible flow and in a really heavy vehicle.

Ford oddly didn't have this problem on the CVH motor or the SHO V6, or the Lima. I'm thinking that it was due to the 3.8L being a bit of a rush job to get on the market with a medium V6
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post #10 of 10 (permalink) Old 01-10-2015, 09:38 PM Thread Starter
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Quote:
Originally Posted by SCTbird1994 View Post
Most of the "head gasket" failures I have seen were the result of an overheated engine, warped head .. not necessarily the gasket itself.
Which came first; the chicken or the egg? Is overheating cause or effect?

1996 Thunderbird LX (4.6), previous daily driver

1995 Mustang GT (5.0), daily driver
1995 GMC C2500 (5.7), alternate daily driver
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