[s-cars] 1995 S6 - Overheating damage, now what?

[Cody Forbes]

Note that in an overheat situation due to lack of coolant the coolant gauge will typically not read accurately. If the sensor isn't immersed in coolant it can't well know the temperature of the coolant. The air in the system at that point becomes an insulator against the heat and the gauge reading will likely go DOWN until the engine gets so incredibly hot that it's transferring enough heat through the threads of the sensor and overcoming the air insulation.

Overheat drama that I've witnessed on race cars:
1) Car is slowly getting hotter due to insufficient cooling capacity or whatever
2) On one lap the driver radios in as he's passing pit lane "hey the coolant temp gauge is almost pegged, coming in next lap"
3) During that lap either the head gasket fails, radiator cap opens to relieve pressure, or by some other means it starts evacuating the hot water
4) Radio transmission "nevermind, the gauge just went down like 30 degrees"
5) one lap later "Hey suddenly it's running bad and there's lots of smoke" at which point the engine has melted down

-Cody (mobile)

On Sep 14, 2011, at 4:39 PM, Andrew B <andrew.sb at gmail.com> wrote:

> I would have to agree; I'd expect to buy a new head, whether reman or from
> another engine.  I bought a car with a bad headgasket, and though I never
> "technically" had an overheating condition (the gauge was always fine), I
> did lose some coolant regularly and have some smoke out the back, but much
> less than yours.
> 
> I took my car to Force5auto where I was told it needed a completely new head
> as the old one was warped out of decking possibility.  It cost me more than
> I expected, and if I could do it again, I'd have the head worked on while
> the car was still running rather than letting it rot in the shop for so
> long.  I would not be surprised, based on my experience, to find out that
> your head is way far gone, and somebody with more experience might be able
> to suggest whether it has piston etc. damage or not.
> 
> On Tue, Sep 13, 2011 at 1:20 PM, Joshua Van Tol <josh at spiny.com> wrote:
> 
>> I'll add a counter point. If the engine was overheated enough, and it
>> sounds
>> like it may have been, the piston skirts could be scuffed, and the rings
>> could be shot. Once the head is off, any scuffing or material transfer on
>> the cylinder walls will be evident. If such damage has occurred, a complete
>> rebuild or replacement is the only option.
>> 
>> If your mechanic has a scope, it may be possible to look at the cylinder
>> walls through the spark plug holes and see if there's any damage to the
>> cylinder walls. Even if your mechanic doesn't have one, they're getting
>> cheap. I saw one at Costco the other day for $180, including a video record
>> function.
>> 
>> Josh
>> 
>> On Tue, Sep 13, 2011 at 11:16 AM, Sean Douglas <quattro20v at shaw.ca> wrote:
>> 
>>> Thomas:
>>> 
>>> I would recommend repairing it. I doubt the engine block is cracked, but
>>> the head is probably warped and the gasket needs replacing.
>>> 
>>> If you motor had good compression before and was not burning excessive
>> oil,
>>> then the piston rings should be fine.
>>> 
>>> I would do pressure test on the head, check the valve guides for wear and
>>> replace them if required. If you replace the guides, then a valve seat
>> grind
>>> is required.
>>> 
>>> I just went through a head rebuild project and the machining was $400 and
>>> the parts came to about $300 including some new coolant hoses and the
>> gasket
>>> kit, new head bolts, etc. I did all the labour myself, but if you were to
>>> pay someone, it would add 6-8 hours labour.
>>> 
>>> Sean Douglas
>>> 1997 S6
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