Which temp sensor feeds the temp guage?

[mckpaul]

Posted this in Engine & Drivetrain, but since this is where the 73-87 guru's are, thought I'd put it here too.....

I have an 84, it doesn't have an ECM, never did. When I got it, it had an 89 motor in it (305). It locked up. Bought a used 86 motor (305) from CRRoy71 here on the board to replace it with. Rebuilt it and now I'm in the process of putting it in.

Here's the deal. Never saw the original 84 305 motor. Both the 89 and 86 motors came from trucks that had an ECM, they have two temp sensors on them, one on the driver side head under the exhaust manifold, and one in the thermostat housing. I think one was to provide a signal to the temp gauge, and the other is for a engine temp signal to the ECM. Since I don't have an ECM, I only have one wire to feed the temp gauge, which is your basic stock gauge with 100 on the low end, 210 in the middle, and 260 on the high end. The wire is long enough to reach either place. I obviously need to plug one of the holes (they are both the same thread but one sensor has a round terminal, one has a spade terminal)

I'm pretty sure I need to use the sensor with the round terminal since that's the one that fits the connector on my wire. But was wondering if anyone had an 84 or earlier stock set up (with no ECM) that could tell me if the sensor should be in the head or in the thremostat housing. And am I on the right track with how it works? Just want to put it back the way it's suppose to be.

[76sierraclassic]

Don't know if this will help or not, but on my '76 350, it's on the driver's side of the engine. I had to replace mine twice recently. It wasn't working at all, so I replaced it, but then it would peg out the temp guage. Turned out I got a defective part and then had to replace that one too. Now it works fine.

Hope this helps. If not, maybe someone else can chime in.

Mike

[mckpaul]

That's the direction I was leaning. I have two threaded holes in the thermostat housing, different sizes. The larger of the two has a four port vacuum switch in it, the smaller of the two is the same size and thread as the hole in the side of the head. Don't know if the thermostat housing is the original or if it came on the 89 enigine. If it turns out the head is the right location for the sensor, I can plug the extra hole in the housing or see if I can find one with one hole at the junk yard. Looked at the chrome ones at the parts places, but they don't have one with a threaded hole at all.
Thanks for the input.

[86-C10-V6]

If you are looking at and 86 305 that did not come from california, the ESC does not have a temp input. What is does have is a knock sensor input that will retard the timing whenever the ECM senses pre-ignition from the knock sensor. The knock sensor is located on the drivers side lower block. The ECM takes the ignition signal from the distributor and passes it back to the distributor. Whenever it senses pinging or whenever the tip in vacuum switch is activated the ECM delays the spark to retard the timing and help stop the pinging and provide better performance.

The temp sensor on the lower left of the block is the sensor for the temp guage.

The one on the manifold is a switch that is used with the dual capacity pump on the quadrajet carb. It decreases the flow of the accelerator pump when the engine is warm. When the thermastatic switch reaches a certain temerature it would energize the valve on the top of the carb which created a bypass for some of the gas coming from the accelerator pump.
Hope this helps.

[mckpaul]

Yep, got a handle on the ESC part of it. That's all I have, I don't have the ECM, that didn't come out until later. But it helps to know what the tip in vacuum switch does, been wondering about that.

Also, my truck came from out of town, all the emission stuff was removed. Have to have all that working here in Houston to pass emissions test, so I'm having to restore it. found an 85 in a junkyard with about 90% of all the vacuum stuff still in tact, and it was about 90% like my vacuum hose routing sticker, only a couple of minor differences. But since it was an 85 that did have the ECM, it had the extra temp sensor on the t-stat housing that was wired to the carb as you mentioned. Came home and looked at my carb, don't have the electrical connector on the top of it like the one in the junkyard had.

Thanks for the help guys, it's all starting to come together.

[nn2004]

Since I have the wiring diagram in front of me, I am 100% certain it is the one on the head of the driver's side. Should have a single wire connector. Mine is a green wire.

[mckpaul]

Thanks. Yep, it's a green wire. When putting the heat shield back under the driver side manifold, I noticed it's even curved to go over the sensor too.
Almost finished last night! Only have to put back the alternator and brackets, belts and fan, carb, and restab the distributor. But it was getting dark and I had been out there since 6:30am, didn't feel like messing with all the tweaking that will be needed cranking off a new rebuild. But soon, very soon...

[nn2004]

Wow, sounds like a busy day. Glad to hear everything is going back together well for ya.