Cylinder Head Temperature

hrafn · Post by **hrafn** » Sun Nov 30, 2008 12:13 pm

Want to add a CHT to your truck?

Here is a "relatively" inexpensive 4 channel device that I installed recently.

Both the meter and the sensors came from Chief Avionics.
http://www.chiefaircraft.com/airsec/Avi ... ngles.html
and
http://www.chiefaircraft.com/airsec/Avi ... nders.html

$200 for the meter and $30 each for the thermocouples.

The meter runs on 24 volts out of the box. The thermocouples are intended to go under the spark plugs,
but I found that it was impossible to do that, so I put the thermocouples under the head bolt above the spark plugs.

The thermocouples only have a three foot wire attached. I had some type K thermocouple wire and connectors
that I used, but maybe you can order the thermocouples with longer leads.

pcolette · Post by **pcolette** » Sun Nov 30, 2008 4:44 pm

Very nice!

Did you use the 10mm thermocouples?

Where would I find Type K thermocouple wire to extend the leads?

Thanks,
Paul

michaelh712 · Post by **michaelh712** » Sun Nov 30, 2008 9:22 pm

Aircraft Spruce

hrafn · Post by **hrafn** » Mon Dec 01, 2008 6:26 am

Paul wrote:

Did you use the 10mm thermocouples?

I bought the 14 mm thermocouples since I originally intended to use the
thermocouples under the spark plugs. That proved to be impossible
because there was not adequate space in the plug well for the spark
plug, the thermocouple wire, and the plug wrench.

I believe 10 mm would be the correct size to put under the head bolt,
although I put the bigger thermocouple on with no problem.

cronapress · Post by **cronapress** » Mon Dec 01, 2008 1:33 pm

I've always thought that the Pinz is a great vehicle "as is". I've never considered buying any add-on goodies at all. That was until I saw this CHT set-up.

IF (big if) I was to spend any spondulixs on a not very vital accessory, then this would be it. The unanswered question seems to be the need for additional wire (is that all it is?) to lengthen the thermocouple leads from the cylinder head bolts to the dash area. Is this just a case of extra length = extra resistance = cocked-up readings ?? A good joint to heavy gauge wire would sort that out, or is that too simple ? Probably.

Winter temps in Scotland can be cool. OK not as "cool" as some of your Stateside temps. I blank over the intake grill for the first few miles to warm the beast up ASAP. Just blind guesswork/smell as to when to remove the blanking (kitchen foil). A temp readout would be quite handy. At this point I ask WHAT is the optimum operating temp. ? Hot enough to vap.off the mayonaise, but not so hot as to worry the snoz whilst driving.

A downside might be, IF I installed this good looking dooferiser, would I just worry all the time that cyl.No.3 is 2 degrees hotter than the rest ?? OMG a burnt valve ? The high-velocity knurl valve fluid retaining nuts are loose ?? Just something (more) to worry about ??

Shipping and our rip-off import taxes on this side of the pond would add to the cost, but ..........

Any comments welcome.

ka · Post by ka » Mon Dec 01, 2008 1:49 pm

hey! your post lit me to the idea of adding remotely operated louvers to the grill of my pinz like the ones installed on big rigs (lorries)!

has anyone done this or seen a source for a system or have any good ideas re designing my own?

hrafn · Post by **hrafn** » Mon Dec 01, 2008 3:59 pm

cronapress wrote:

The unanswered question seems to be the need for additional wire
(is that all it is?) to lengthen the thermocouple leads from the cylinder
head bolts to the dash area. Is this just a case of extra length = extra
resistance = cocked-up readings ?? A good joint to heavy gauge wire
would sort that out, or is that too simple ?

I do believe you could probably order the thermocouples with longer
leads. Might be a special order, higher cost, longer wait, etc., but that
would be ideal.

Please note: You cannot simply lengthen the leads by using copper
wire! You must use Type K thermocouple wire. Also, any
connectors (such as those that I used) must be Type K connectors. I had
some Omega (http://www.omega.com/) connectors and Type K wire
left over from another project. You could also probably order
Type K thermocouples directly from Omega at a comparable price.

One more thing: Polarity on the wires and the connectors is important.

would I just worry all the time that cyl.No.3 is 2 degrees hotter than the rest ??

An old-timer Volkswagen mechanic told me that ten or fifteen degrees
difference between cylinders is nothing to worry about. I rarely see
more thant ten degrees difference.

hrafn · Post by **hrafn** » Sun Feb 01, 2009 1:32 pm

I have been asked a question via a PM, but I thought that I should post the answer here for all.

The question was regarding where to mount the thermocouple since it is almost impossible to mount
it under the spark plug. Initially I put the the 10 mm ring thermocouple under the lower head bolt
(as indicated by the arrow in the photo below). However, on the new engine I am building I drilled
and tapped a 6mm hole in the cooling fin just below the head bolt. I also will be using 1/4" Type K
ring thermocouples from Omega Engineering. These thermocouples have a nice armored cable
and are actually less costly than those I got with the CHT meter.

The thing to remember with a CHT is that actual temperature is not as important as relative temperature.
You want to see the differences between cylinders - that's where any indication of problems will show up.
My CHT's are generally within 10°F of each other.

An added benefit of ordering the thermocouples from Omega Engineering is that you can order the exact
lengths required, thus eliminating connectors and extension cables.

MASSIVE PINZ · Post by **MASSIVE PINZ** » Mon Feb 02, 2009 5:01 pm

You may be seeing temperatures well over 100F lower than the spark plug area with the senders in the cooling fins, that far from the chamber.

Been there, done that with 26 sensors and a data logger on the same engine.. The fins are the coolest running portion of the head.

hrafn · Post by **hrafn** » Mon Feb 02, 2009 5:26 pm

MASSIVE PINZ wrote:You may be seeing temperatures well over 100F lower than the spark plug
area with the senders in the cooling fins, that far from the chamber.

Been there, done that with 26 sensors and a data logger on the same engine..
The fins are the coolest running portion of the head.

I am well aware of that fact, Jake, however, because of the deep, narrow spark plug wells,
it is nearly impossible to get a thermocouple under the spark plug without destroying it.
The thermocouple would surely be destroyed after just a few spark plug changes.
My alternate attachment site is as close as possible to the exhaust.

I suppose it might also be possible to put the thermocouple on one of the
exhaust manifold studs.

Also, I might suggest that not everybody has access or funds to use 26 sensors
and a data logger. The purpose of this thread was to provide information on a
relatively inexpensive four channel CHT. I believe that the relative temperature
difference between cylinders is far more indicative of problems than the absolute
temperature.

MASSIVE PINZ · Post by **MASSIVE PINZ** » Mon Feb 02, 2009 8:15 pm

Yep I am fully aware of those challenges.... I ended up using the K type units from my Dyno to do the test work... The plug holes are very deep and very tight..

I ended up using JB weld to affix the TC to the area around the plug hole, so it would stay in place at plug changes.. That worked well.

Bruce Berger · Post by **Bruce Berger** » Tue Feb 03, 2009 8:26 pm

So what's the highest temperature you can expect to see measured on the cooling fin? I recall the guys in AZ mentioning once that they never saw anything higher than 180 degrees (F) regardless of the ambient temperature.

M Wehrman · Post by **M Wehrman** » Wed Feb 04, 2009 11:55 am

I don't know about the head temp here in AZ,but I"ve seen oil temps in excess of 200 degrees. I would think the head would be hotter..
Mark

MASSIVE PINZ · Post by **MASSIVE PINZ** » Wed Feb 04, 2009 1:29 pm

I saw 325F most of the time.. Up to 400 pulling long hills in the summer

In the fins I measured a 150F difference, but thats not very accurate since there are so many different places the sensor could be mounted in the fins.

Under the plug is the data that we use for comparative purposes.