Valve stem seals.....

[mrvette]

How hot can an engine get before damaging/melting? the valve stem seals?? thinking of my '89 truck block, L98 heads, roller cam/rockers...

it has seen as high as ~230f

[Steve_R]

230 shouldn't damage anything. Those seals can get brittle or worn over time, but that temp isn't going to melt them - not even close.

[Rodnok1]

Originally Posted by Steve_R

230 shouldn't damage anything. Those seals can get brittle or worn over time, but that temp isn't going to melt them - not even close.

230 is just getting warmed up.

[Torqaholic]

You'd need to identify the material being used to answer such a question.


This may help?

https://www.enginebuildermag.com/199...s-and-designs/

...the material used may be nitrile, polyacrylate, fluoroelastomer
(Viton), silicone, nylon or Teflon¨.

Nitrile is one of the least expensive materials, and has been used for many years in umbrella or deflector type seals for older pushrod engines. Nitrile’s temperature range is -40º to 250º F. It can withstand
intermittent operating temperatures of up to 300º F, which
is usually good enough for intake valve seals but not exhaust
valve seals.

A step up from nitrile is polyacrylate. Polyacrylate
is about twice the cost of nitrile and has a temperature range
of -30º to 350º F; it is a good step up from nitrile
for umbrella seals. It is also used for some positive seals as
well.Some engines such as older big block Chevy V8s have positive
seals made of nylon. Nylon is a hard material with a temperature
rating of -40º to 300º F. Nylon is impervious to oil,
but it can melt if the engine overheats.

A higher grade seal material is silicone, which is rated from -60º to over 400º F, depending on the grade of the material. Some silicone seals can operate at 330º F continuously and handle up to 400º
F intermittently, while others can take 375º and go as high
as 450º to 500º F intermittently without damage. Silicone
is a good high-temperature material, but costs four to five times
as much as nitrile.

In the mid-1980s, positive valve stem seals made of fluoroelastomer materials (FKM and Viton) began to appear in import and domestic overhead cam engines. Fluoroelastomer seals cost roughly 12 times as much as nitrile, but have a temperature range of -5º to 450º F, making them one of the best
high-temperature seals available.

Viton has good flexibility like nitrile, which means it can handle some runout between the valve stem and guide. It is also considered to be a more durable material than silicone. Viton also has better wear resistance than most other seal materials, making it a good choice for applications
where long term durability is a must.

The highest rated positive seal material is Teflon, with a range of -5º to 600º
F. Like nylon, Teflon is a hard material so it cannot handle as
much runout between the stem and guide as more flexible seal materials
can. What’s more, Teflon is expensive – costing 20 to 25 times
as much as nitrile.

Material identification
It’s important to know what type of material the valve stem seals are made of when rebuilding an engine so you can replace same with same, or
better. Upgrading to a better grade of material should certainly
be considered if the original seals are badly deteriorated and
you have a choice as to the type of seal material that’s available
for the engine. Upgrading from nitrile to polyacrylate, silicone
or Viton, for example, would provide better durability and longevity
if the original nitrile seals were found to be hardened or falling
apart.

Identifying seal material
How can you tell one type of seal material from another? Color is not necessarily an accurate guide because the same material may come in several different colors. Nitrile seals may be black, green or blue. Polyacrylate is usually black, while Viton may be brown, orange or black. Nylon has a translucent appearance while Teflon is white. Silicone is
usually black.

Replacement seals may not be the same color as the
OEM seals even if the materials are identical, while others may
be the same color but made of a different material. The color
identification information contained in some OEM service manuals
is also inaccurate. So going by color alone is not a very good
way to tell what type of material is in a valve stem seal.

Some engines may also have two different types of seal materials which
may be color coded to distinguish the intake and exhaust valve
guide seals (a higher temperature material being used for the
exhaust valves). AERA has published a technical bulletin (September
1997, TB 1488) identifying the seals used in 1984 to ’96 Chrysler/Jeep
2.5L and 4.0L engines. On this application, black seals (polyacrylate)
are used on the intake valves and brown seals (Viton) are used
on the exhaust valves.One way to identify an unknown seal material
is with a burn test:

Nitrile will burn easily and produce thick black smoke that
smells like burning rubber.

Polyacrylate will also burn easily producing a less dense
black smoke that smells like burning plastic.

Silicone will turn white when burned, regardless of the original
color of the seal, producing smoke that has little color and no
odor.

Viton/fluoroelastomer seals will be difficult to burn and
produce white smoke with no odor. The seal color will either remain
the same or turn black.