What can cause a hot CHT?

[Ron Garret]

This has now happened to me several times: one of my CHT temps will
bounce around between normal and off-the-scale hot, and sometimes will
cut out entirely. All other indications (EGTs, the other CHTS, oil
temp, airspeed etc.) are normal.

This has happened before and replacing the CHT probe fixed the problem.

Trick is, 1) it's happening a lot (thank god the thing is still under
warranty or I'd be spending of money on probes) and 2) this only happens
when the engine is at full power. If it's close to idle the CHT reads
normal. This makes me think that it is NOT (just) a bad probe. On the
other hand, it seems physically impossible for the readings to be real
because it seems physically impossible for a cylinder head temp to rise
and fall that fast (+/- 200 degrees in a second or two).

What could be causing this? Is it potentially hazardous?

Thanks,
rg

[Orval Fairbairn]

In article >,
Ron Garret > wrote:

> This has now happened to me several times: one of my CHT temps will
> bounce around between normal and off-the-scale hot, and sometimes will
> cut out entirely. All other indications (EGTs, the other CHTS, oil
> temp, airspeed etc.) are normal.
>
> This has happened before and replacing the CHT probe fixed the problem.
>
> Trick is, 1) it's happening a lot (thank god the thing is still under
> warranty or I'd be spending of money on probes) and 2) this only happens
> when the engine is at full power. If it's close to idle the CHT reads
> normal. This makes me think that it is NOT (just) a bad probe. On the
> other hand, it seems physically impossible for the readings to be real
> because it seems physically impossible for a cylinder head temp to rise
> and fall that fast (+/- 200 degrees in a second or two).
>
> What could be causing this? Is it potentially hazardous?
>
> Thanks,
> rg

It could be a faulty wire that is about to break at a connection, or a
thermocouple that is not properly secured in the cylinder head.

[Ron Garret]

In article >,
Orval Fairbairn > wrote:

> In article >,
> Ron Garret > wrote:
>
> > This has now happened to me several times: one of my CHT temps will
> > bounce around between normal and off-the-scale hot, and sometimes will
> > cut out entirely. All other indications (EGTs, the other CHTS, oil
> > temp, airspeed etc.) are normal.
> >
> > This has happened before and replacing the CHT probe fixed the problem.
> >
> > Trick is, 1) it's happening a lot (thank god the thing is still under
> > warranty or I'd be spending of money on probes) and 2) this only happens
> > when the engine is at full power. If it's close to idle the CHT reads
> > normal. This makes me think that it is NOT (just) a bad probe. On the
> > other hand, it seems physically impossible for the readings to be real
> > because it seems physically impossible for a cylinder head temp to rise
> > and fall that fast (+/- 200 degrees in a second or two).
> >
> > What could be causing this? Is it potentially hazardous?
> >
> > Thanks,
> > rg
>
> It could be a faulty wire that is about to break at a connection, or a
> thermocouple that is not properly secured in the cylinder head.

I thought about that, but why would that make it read hot? If the
thermocouple is not properly secured shouldn't it read cool, not hot?
And if the wire is broken, shouldn't the readings just be all over the
place? They aren't, they are either normal, or hot, or blank, never
cool. And only at full power.

rg

[Ron Garret]

In article >,
Ron Garret > wrote:

> In article >,
> Orval Fairbairn > wrote:
>
> > In article >,
> > Ron Garret > wrote:
> >
> > > This has now happened to me several times: one of my CHT temps will
> > > bounce around between normal and off-the-scale hot, and sometimes will
> > > cut out entirely. All other indications (EGTs, the other CHTS, oil
> > > temp, airspeed etc.) are normal.
> > >
> > > This has happened before and replacing the CHT probe fixed the problem.
> > >
> > > Trick is, 1) it's happening a lot (thank god the thing is still under
> > > warranty or I'd be spending of money on probes) and 2) this only happens
> > > when the engine is at full power. If it's close to idle the CHT reads
> > > normal. This makes me think that it is NOT (just) a bad probe. On the
> > > other hand, it seems physically impossible for the readings to be real
> > > because it seems physically impossible for a cylinder head temp to rise
> > > and fall that fast (+/- 200 degrees in a second or two).
> > >
> > > What could be causing this? Is it potentially hazardous?
> > >
> > > Thanks,
> > > rg
> >
> > It could be a faulty wire that is about to break at a connection, or a
> > thermocouple that is not properly secured in the cylinder head.
>
> I thought about that, but why would that make it read hot? If the
> thermocouple is not properly secured shouldn't it read cool, not hot?
> And if the wire is broken, shouldn't the readings just be all over the
> place? They aren't, they are either normal, or hot, or blank, never
> cool. And only at full power.
>
> rg

Update: I am told that there is a service bulletin out for loose
connections to CHT probes on Cirri. So that's probably what the problem
was.

rg