CHT Sensor Replacement

[Targa Me]

I changed my CHT sensor yesterday and I thought I'd post my DIY info.

My car was running rich at start up and when I tested the CHT there was no reading from my DMM (digital multi-meter).

Tools:
14mm open end/box end wrench.
1/4 inch drive extensions, handle and 8 point socket.
10 x 1.00mm tap
Stubby rachet
(Prep tools):
Propane torch
Fiber cutting wheel.
Vise
Hammer


Place the wrench in your vise, secure it and then heat.
Next I began tapping on the box end portion with the hammer to make my bend.

This is what you should end up with.


Now with your cutting wheel, cut a slit in the box portion of the wrench wide enough for the CHT wire to fit through.


NOTE: Some people cut the wire off the old CHT and use a socket to remove the old sensor. I didn't do that because if my DMM reading was wrong, (LOL it's happend to me before) by not cutting the wire I now have saved the old CHT from a misdiagnosis and have a spare.

Unplug the CHT from the harness in the engine compartment.
Now with your car on a jack stand and then left rear wheel removed you now have access to the CHT.

Remove the rubber gromment on the engine tin.
Slide the CHT wire through the cut in the wrench and place hex end over the CHT.
Now use the stubby rachet on the open end of the wrench to turn the wrench. You don't need a stubby, you can use anything you have that'll fit the wrench to twist.



Once you have the CHT removed you may want to clean up the threads with your tap.
I used a 1/4 inch drive extentions and handle to turn the tap.
Take caution when turning the tap; you want to trace the original threads, not make new ones. I used WD40 as a lubricant for the tap.
When you are tapping the threads you want to twist the tap and then back up on the threads and then twist again a little further until you've reached the bottom of the threaded cavity.
Once this is done, clean out the cutting.
Now you're ready to thread the new CHT in. Once again use caution when threading the new CHT in, you don't want to cross-thread.

Now you can feed the wire through the engine tin and plug the connector to the wire harness.

(This is my first Tech post, I hope it makes sense to everyone.)

Here are some photos of the tools.

[wolf76]

Nice write up. This project is on my to do list so I'm sure it will come in handy. By the way, how hard was the grommet to remove? What was the difficult part of the job?



Thanks,

Chris

[Targa Me]

Wolf, removing the gromment was not hard at all. When installing the new CHT gromment I put a little vaseline around the edge of the gromment and it slipped right into place.

This job was not difficult at all; I would have to say the hardest thing was making sure that tap was started correctly and the second tricky thing was that the new CHT was started/threaded in correctly.

The last thing you want to do is cross thread the tap or CHT.

[wolf76]

I will definitely be rereading this and probably printing it out as well before I attempt mine. Thanks again for the writeup.



Chris

[chateau]

Wish I had seen this before I did mine!!

[Joe6pack]

Perhaps someone can help me here. I am about to do the same task. However, the CHT sensor pigtail in my 1987 Carrera has only one male terminal and according to the Bentley manual it should have two. I am thinking that I have the wrong CHT in there now. Was there ever a one wire CHT sensor? I ordered a CHT sensor from Pelican yesterday for an '84-'89 Carrera, so it should be correct. At this point, I am just trying to figure out what is going on. My idle is rough, so I am hoping this will correct it.

Thanks,

John

[175K911]

Very well done first tech post. Thanks for sharing.

I did mine for the first time probably 20 yrs ago, trackside. Instead of cutting and bending a box wrench, I cut a slot up the side of a deep well 6 point SnapOn 14mm socket. Being 350 miles from home at the Glen, that's what I had to work with. But I continue to use that old socket to this day, much easier to remove and install with just a 3/8 ratchet and long wobbly extension. Just need a socket deep enough that the slot allows the wire to come out the side.

[syncroid]

The new head temp sensor is a two wire sensor. The old one is a single wire.

[rcaradimos]

Head Temperature Sensor Replacement
More good information!

[polizei]

Great write up! I used Targa Me's instructions last night, and it worked great. Getting the new CHT sensor to thread-in was the biggest challenge for me. I found that separating the rear shock from the control arm made a good bit more room for maneuvering.

Thanks!

[jlex]

I also cut a slot in a long socket to remove the CHT sensor. Getting the new one in without cross-threading it, like others have said, is a real job. Problem is the wire is attached, and it wants to throw it off kilter when trying to get the new one started. What I had to do is before you start screwing it in is to hold the wire at the end, then turn the sensor counter clockwise a couple of turns to help counter the wire's pull. That's what I had to do... Did the reference and speed sensors at the same time as they share the same grommet.....

[edesign45]

Originally Posted by jlex

I also cut a slot in a long socket to remove the CHT sensor. Getting the new one in without cross-threading it, like others have said, is a real job. Problem is the wire is attached, and it wants to throw it off kilter when trying to get the new one started. What I had to do is before you start screwing it in is to hold the wire at the end, then turn the sensor counter clockwise a couple of turns to help counter the wire's pull. That's what I had to do... Did the reference and speed sensors at the same time as they share the same grommet.....

Yes, this method works great. see pic.

[jlex]

Great picture. Best to check your CHT size before cutting into sockets. The new & old sensors were the same size on my '88, although I thought I read where some cars had different sensor sizes between the new and old. I'd wait 'til I had the new one in hand before I did any cutting.

[darrin]

you can also cut the wire on the old CHT and use an un-cut socket to remove -- then hand-tighten in the new CHT and use needle nose pliers to snug in -- did mine this way around a decade ago and it's still tight

[wrxnofx]

I did this job last summer, and like other had said the hardest part of this job by far was getting the new sensor threaded. The wire kept twisting it back out when I thought I had it started. I ended up also buying a tap and retapping the threads. As soon as I did that it went on first try.