I need to pick up a CHT gauge and sender and was wondering where the sender mounts on a 2.7L six?

Doug C

under a spark plug on whatever engine you've got...

with only one, i think i'd use #6. it's the farthest from the fan and it's next to the oil cooler. it's also (in a 914) the most-aft cylinder and above the most exhaust pipe.

if i were doing one per side, i think it'd be #6 and #3 (the most rearward on the other side).

I have no idea what the senders look like..do they fit in the sparkplug hole (like a washer for the plug) or what? I have noticed some small allen head bolts in the area below the plugs, maybe those are utilized for the CHT senders? Also, can I run two senders for one gauge? Does your gauge reading then become an average of the two?

Here's another (related) question - When folks use the double sender for the pressure gauge (includes idiot light) and mount it next to the fan housing what then happens which the sender placed back above the flywheel area? Is it used for anything? Any real reason to use a double?

Doug C

The sender is a big ring terminal, and fits under the plug's washer. You can run N senders with one gauge, but you need to rig up a switch to connect both sender wires to the gauge input wires (so a double-pole, double-throw (DPDT) switch can do two senders with one gauge). Under the plug is the only accurate place to put them. The head does not get to a uniform temp, and under the plug gets you as close as possible to the combustion chamber, which is what you're really trying to measure.

QUOTE (DougC @ Aug 18 2005, 02:41 PM)

I have noticed some small allen head bolts in the area below the plugs, maybe those are utilized for the CHT senders? Here's another (related) question - When folks use the double sender for the pressure gauge (includes idiot light) and mount it next to the fan housing what then happens which the sender placed back above the flywheel area? Is it used for anything? Any real reason to use a double?

how small? i'm having a hard time picturing "small" Allen bolts on the head - but i think you may be referring to the inhex barrel nuts that hold the cam towers to the heads. IAC - the sender goes under the spark plug. one per gauge, unless you switch them as noted. or you use multiple-gauge heads - aircraft use these all the time.

i don't think there's a reason to use two oil pressure switch senders. pick one. i'd use the one the factory uses and ignore the switch portion of the combo sender.

my car doesn't have a light, (and my engine came with no switch...) so i need to pick up a switch, wire it to a light i don't have, *and* relocate the pressure gauge sender...

I dunno why your car came w/o a light and switch, every 911 of that vintage I've ever seen has a light in addition to the gauge. The Cap'n

QUOTE (Cap'n Krusty @ Aug 18 2005, 03:07 PM)

I dunno why your car came w/o a light and switch, every 911 of that vintage I've ever seen has a light in addition to the gauge. The Cap'n

check the spec book -- 2,2 E and S have pressure gauge only - no switch. T's had the switch.

I have the same issue

The spark plug installation is a BIG pain. I haven't done any measuring yet but how different do you think the temp at the exhaust header point of connection to the heads would be off? I think this installation would be close enough.

Since the temp is not exact in either location I think the header installation is just as good. Once you adjust for the new location and get your engine’s "Standard" operating temp (base temp) you will be able to tell if your running hotter then your base temp. This is all I use my gauge for. It just tells me if I am running hotter then normal. What the temp is doesn't matter too much it’s the delta T you need to look for. If your delta T is 10 or 50 degrees off normal you need to respond to each in the correct way

Just my thoughts..

QUOTE (Kerrys914 @ Aug 18 2005, 03:21 PM)

...how different do you think the temp at the exhaust header point of connection to the heads would be off?

i did this on the last car i ran a CHT (a T-III). i wish now i'd compared the two locations but oh well...

the exhaust flange location is going to be affected by EGT - which often moves in the opposite direction of CHT in response to tuning changes.

aircraft use CHT and EGT gauges because they have operator-controlled mixture setting and radically different power regimes (roughly: takeoff, climb, cruise, descent). we (well - most of us...) don't have in-flight programmable mixture.

there's something to be said for monitoring oil temp for indication of overheating - and using the alternator light as a sensor for excessive CHT (when the belt breaks, the fan stops...)

i wonder if it's possible to get thermocouple rings for 12mm plugs?

There's nothing magic about the rings. They're just Al that's crimped to junction of the thermocouple wires to transfer the heat. It's those wires inside the braid that are "special". Just uncrimp the stock ring, make a new ring, and crimp it on.