Alternative location for Cylinder Head Temp Sender, Considering one of the #3 Cylinder exhaust studs Options

[bobhasissues]

I have some new 914 2.0 repro heads from DRD. The new heads use a 12mm spark plug rather than the stock 14mm. I want to use a ring terminal type Cylinder Head Temperature Sender under the #3 spark plug just as I did on my stock heads. The problem is the outside diameter of the ring terminal of my 12mm CHT sender is larger than the bore of the spark plug hole so I can't put the sender under the #3 plug as designed. As many of you probably do, I had the 14mm ring terminal sender on my stock heads and that took a lot of manipulating of the terminal stem to get it to fit. This is way worse, the OD of the 12mm ring will not even fit into the plug bore.

I asked Darren at DRD what to do and he suggested to use the fuel injection CHT location out on a fin by the intake manifold. I don't like that idea because it seems too far away from the chambers to pick up any major temp fluctuations.

I'm considering changing to an 8mm ring terminal on the sender and double nutting it onto one of the #3 exhaust studs.

Anyone have a better location?

[Jake Raby]

Without the sensor under the plug the values that you will gather is virtually worthless. I have applied as many as 16 sensors on a single engine at once in positions all over the cylinders and heads. I saw as much as a 200 degree differential between hottest and coolest reading simultaneously.
What this proved to me was the ONLY place for that sensor was under the spark plug.

The entire head doesn't achieve a single temperature, under the plug gives the most repeatable readings. With a sensor under an exhaust stud you will have insanely high temps as exhaust gas temps run 9-1200 degrees and heat soka the entire area around the exhaust port.

I'd recommend modifying the plug well to accept the proper sensor (our heads have this done as standard offerings) and you can buy various size ring terminal sensors from Westach and Dakota Digital.

Values are no good if they aren't accurate.

[Valy]

What is the expected range of the head temperature?

[Jake Raby]

Dependent on load CHT can vary from 250-450 degrees.. Values can differ 100 degrees in just one mile of driving in certain road conditions.

[tradisrad]

I recently put in a CHT. I typically see temps around 350 with spikes near 400. The temps vary a lot during a typical drive. I installed it with the engine in the car.

My friend had taken a spark plug and cut it in half, leaving only the threads, filed it with epoxy and put a screw driver slot in the epoxy. I used his "plug" in my spark plug hole while I used a dremmel to modify the head to accept the ring terminal. No metal in the eninge.

Jake,
I have read numerous places about the inaccuracy of the VDO gauge; especially since the cold end of the thermocouple is in the hot engine bay. What do you have to say about this?

I've thought of making my own sender and running thermocouple wire all the way to the center console. I've contacted Digital Dakota and they can make a special wire with the 14mm ring terminal and the length I would need for about $20.

[r_towle]

if you are using the cht value to run a fuel injection system, then you need to find a way to put it back on a plug till you reprogram your FI for the next location.

If you are not using an EFI system that relies on that CHT, you can put it where ever you want.

Many people run with no Cylinder Head temp gauge and the car still runs.
Do your heads have the bung drilled and tapped for the original CHT that is next to the #3 intake head bolt?

I would not put it on the exhaust stud until you verify the gauge and sender can deal with that much heat...
EGT sensors are designed for the very high temp of the exhaust, but not the typical CHT sender or gauge.


Rich

[majkos]

Have them make a couple extra,
Digital Dakota 'cause I sure can use one and thats a good deal (IMG:style_emoticons/default/aktion035.gif)

[Jake Raby]

The stock CHT position for the EFI system is also inaccurate for CHT values and monitoring. That sampling position was specifically positioned to protect the switch from too much heat as well as to remain hot for a longer period of time after engine shut down.

That position is at minimum 100F lower than the under plug sampling location. I have multitudes of that supporting data.

[SirAndy]

That position is at minimum 100F lower than the under plug sampling location.

Well, if you know it's always going to be about 100F lower in that position, you can easily design your FI logic to compensate for that and still be reasonably accurate.

(IMG:style_emoticons/default/shades.gif)

[r_towle]

That position is at minimum 100F lower than the under plug sampling location.

Well, if you know it's always going to be about 100F lower in that position, you can easily design your FI logic to compensate for that and still be reasonably accurate.

(IMG:style_emoticons/default/shades.gif)

zactly

[Valy]

That position is at minimum 100F lower than the under plug sampling location.

Well, if you know it's always going to be about 100F lower in that position, you can easily design your FI logic to compensate for that and still be reasonably accurate.

(IMG:style_emoticons/default/shades.gif)

zactly

So if I use the stock location for the temp sensor, would a normal gauge of up to 350F work?

[Jake Raby]

That position is at minimum 100F lower than the under plug sampling location.

Well, if you know it's always going to be about 100F lower in that position, you can easily design your FI logic to compensate for that and still be reasonably accurate.

(IMG:style_emoticons/default/shades.gif)

Problem is the fact it isn't absolute... Thermal conductivity of different head castings creates a variable. One degree separates safety or failure.

I have never had an issue with spark plug senders; I only changed the plugs twice in my 912E engine in 8 years and 160,000 miles.. The senders under my plugs have been in service since 2002 and still are in service today. No need in changing plugs as often as most people do with these engines.

[76-914]

(IMG:style_emoticons/default/hijacked.gif) Sorry for the highjack but this seemed a good time and place to ask this:
What milivolt values should I see fromm the Dakota plug style thermocouple and it is compatible w/ the VDO gage? Also, how can I test a VDO gage if I suspect it is not working? TIA and sorry for the highjack, again.

[wndsrfr]

I had the same issue with the 12mm plug and got some excellent support from "The sensor connection" guys. They worked with me sending back & forth several CHT's and finally got it right with a 12mm ring that will actually fit down in the recess on the head. Mind you, it's still a tight fit & you have to carefully bend up the tab, but their 12mm ring is a true 12mm, not 13mm as some vendors are supplying. No vested interest, just have had great service from these folks:
http://www.thesensorconnection.com/index.shtml

[bobhasissues]

http://www.thesensorconnection.com/index.shtml[/url]

Just when I was ready to give up on an under plug sender.
Perfect, Problem solved!


Thanks for the link

[rick 918-S]

I have the factory CHTS in the right head. Should I be running the plug style instead? Do they wire in the same?

[r_towle]

If you are using the cht for the fuel injection, you must use the stock location, stock sensor etc.
If you are using that reading for either an aftermarket gauge or aftermarket fuel injection, you can use the plug sensor.

In your cold weather location, you may want to contact Brad and get his spacer for the sensor to give your car a bit more time on warm up....at 914ltd in Illinois

Rich

[rick 918-S]

If you are using the cht for the fuel injection, you must use the stock location, stock sensor etc.
If you are using that reading for either an aftermarket gauge or aftermarket fuel injection, you can use the plug sensor.

In your cold weather location, you may want to contact Brad and get his spacer for the sensor to give your car a bit more time on warm up....at 914ltd in Illinois

Rich

Aaah.. I thought this was some new fangled thing I needed. I'm cool.

[r_towle]

nope, you just need to start the damn thing already...
What is missing?

Rich

[913B]

I had the same issue with the 12mm plug and got some excellent support from "The sensor connection" guys. They worked with me sending back & forth several CHT's and finally got it right with a 12mm ring that will actually fit down in the recess on the head. Mind you, it's still a tight fit & you have to carefully bend up the tab, but their 12mm ring is a true 12mm, not 13mm as some vendors are supplying. No vested interest, just have had great service from these folks:
http://www.thesensorconnection.com/index.shtml

Sorry but I am reviving this old thread. I want to install the CHT under the spark plug like all the cools kids have. So is this the one to get or have there been better solutions? I am preparing myself for the idea of dropping the engine to perform the modification on the head. That's not the only reason to drop the engine. I need to install the crank sensor for my Microsquirt conversion too.

Thanks All!