problem with HOT engine

[James Sweet]

Yikes! No! Never try to remove a spark plug while the head is hot; there
is a high probability of damaging the threads in the head. If that
happens,
the cheap fix is a Helicoil; the expensive fix is a new head.

Why? The head expands a bit faster than the plugs, usually they're easier to
remove when hot. I would however wait for the head to cool before installing
them.

 

[Michael Pardee]

Why? The head expands a bit faster than the plugs, usually they're easier
to remove when hot. I would however wait for the head to cool before
installing them.

OTOH, the aluminum is softer and more reactive ("sticky") when hot. Good
news, bad news. I stick with cold engines for plug removal and installation,
so I can't say whether hot engines are bad.

Mike

 

[Knut Solem]

If the head was that hot from a mixture/timing issue, the incandescent
glow from the exhaust manifold and turbo would give it away.

Not always.
Depends on dimension on the axhaust pipe and pressure in the axhaust system.
Turbo or not will also make a difference.
But may occure when car is run under heavy load or hard accelleration.


Anyway, check for coolant flow in the cylinder head.
Possible problem is the coolant pump.
Or wrong replaced hoses...

Yikes! No! Never try to remove a spark plug while the head is hot; there
is a high probability of damaging the threads in the head. If that
happens,
the cheap fix is a Helicoil; the expensive fix is a new head.

Not that hot...
Not red hot. Just so hot that the engine don't run under starting (cold
engine) conditions.
You can't tell anything from spark plugs run with extra fuel added (starting
conditions or cold engine conditions adds extra fuel).

If you have a Haynes manual for the car, you can find a color chart for
spark plugs on one of the last pages in the book.

[ ... ]

That color chart applies when the plugs are cold, not hot.

But the pictures are to compare with spark plugs run under normal hot engine
conditions.
So if you can run the engine so the engine temp rises to normal running
conditions. Then stop and wait until the engine gets cold. Takes a few
minutes... At least 30. It's ok for me, but it's almost 30 min of wasted
time in my eyes...

I've removed spark plugs from hundreds of hot engines for more than 25 years
now, without any problems. If the spark plugs are tightened with the right
torque, it should be no problem. But be careful anyway. If it seems to be
stuck, dont use extra force... Wait until the engine gets cold, and try
again.

 

[Michael Pardee]

You can't tell anything from spark plugs run with extra fuel added
(starting conditions or cold engine conditions adds extra fuel).

But that's why you want to check the color on the plugs when they are cold.
The last time the plugs were used the engine was warm - it is best to do it
after some actual driving

Mike