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Index > Engine/Drivetrain > Thread: coolant sensor question
Thread: coolant sensor question
mwpayne


Hauling
Posts: 195
posted February 13, 2008 08:29 PM
Edited By: mwpayne on 13 Feb 2008 20:34

Coolant sensor question

My choke stays out at all times while switch is on. I believe the culprit is the temp sensor on the thermostat housing. Are these the same as the RX7 ones? Mine reads .6 ohms, hot or cold (I removed it and submersed it in hot water to check). If so, maybe it's obtainable.
Also, I have another coolant sensor on top of the engine block, apparently unused. I'm thinking of just using it for the choke switch, swapping plugs, etc.
I'm wondering if the SA,FB,FC,FD coolant sensors can be used...long shot probably.

       
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kansei


Redlining
Wankelized
Posts: 423
posted February 14, 2008 06:59 PM
Edited By: kansei on 14 Feb 2008 19:01

Mike,

If your truck originally came equipped with the water thermosensor (on the top of the center housing), as all '74s did, it should be plugged in (you mentioned yours is "unused"). Without that plugged in and your magnetic switch in the choke switch assembly working properly, it will never retract. The water temp sender on the water pump housing/thermostat housing does not independently operate the automatic choke on a '74, it is controlled by the thermosensor.

Neal.
____________
Neal A.E. Swigert
Greenville, Michigan
1974 REPU Resto Project
1976 808 Wagon
1977 Cosmo
1978 Savanna RX-7 GT
1980 Leather Sport RX-7
1980 Petty Targa RX-7 #11
1985 GSL-SE RX-7
1988 RX-7 10th Ann
1993 RX-7 VR Touring




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mwpayne


Hauling
Posts: 195
posted February 16, 2008 05:21 AM
Edited By: mwpayne on 16 Feb 2008 05:22

Oh! Thanks kansei, I thought the one on the T-Stat housing was used for the choke, but I guess I had them mixed up.
The choke knob won't retract (even if water thermistor plugged in) unless switch is off.
Guess the T-Stat one was used for emissions?

       
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kansei


Redlining
Wankelized
Posts: 423
posted February 16, 2008 07:35 AM
Edited By: kansei on 16 Feb 2008 07:40

Well, the sensor on the thermostat housing does affect the choke (especially on post '74 models), but on the '74s the thermosensor on top of the engine ultimately dictates when the choke is retracted. And you are correct, on a 12A RX-7, the sensor on the thermostat/water pump housing does control the choke.

I discovered this after researching the wiring diagrams and thumbing through the Rotary Pickup Emissions System booklet. I had the same problem when I got Andy's old engine (1975 model, sans thermosensor) in my 1974 chassis and had to figure out why the choke wasn't retracting. The 1974s lack the oil level sensor, which the 1975s did have. I also found that my 1975 engine (that was originally behind an automatic trans) does not have an oil pressure sensor, it has an allen plug from the factory. The emissions system on the 1975 (Andy's truck was also a California spec model) has a few extras my 1974 was missing (it was also a California model when new). I am posting all of this because different model years and California vs non-California spec trucks can have different sensors and emissions stuff that could cause similar headaches, but get solved through different courses of repair/replacement.

You also need to keep in mind that even with the thermosensor plugged in, it could be bad (they did corrode) and malfunctioning. Your choke switch could also be bad, and the electromagnet may be toast (I have had two go out on 1979-1983 RX-7s before). Keep in mind the choke switch for a 1974 is different from a 1975+ model, in case you need to replace it.

Neal.
____________
Neal A.E. Swigert
Greenville, Michigan
1974 REPU Resto Project
1976 808 Wagon
1977 Cosmo
1978 Savanna RX-7 GT
1980 Leather Sport RX-7
1980 Petty Targa RX-7 #11
1985 GSL-SE RX-7
1988 RX-7 10th Ann
1993 RX-7 VR Touring




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mwpayne


Hauling
Posts: 195
posted February 17, 2008 01:33 PM

Neal

Wealth of info there, many thanks. I did remove the sensor from the engine block, put a meter on it, then submersed it in hot water. It seemed to work..assuming the changing values are correct. Did the same with the other one, it showed .6 ohms, hot or cold. That's why I suspected it keeping the choke magnet energized.
I could put a switch on it as a stopgap until I figure it out, I guess.

       
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kansei


Redlining
Wankelized
Posts: 423
posted February 17, 2008 02:07 PM

Well, you obviously need to replace the other sensor, and then I'll bet it all works, provided your choke switch itself is fine.

Not sure about using an RX-7 sensor in the bad one's place, as I am not sure it operates on the same resistance levels.

Neal.
____________
Neal A.E. Swigert
Greenville, Michigan
1974 REPU Resto Project
1976 808 Wagon
1977 Cosmo
1978 Savanna RX-7 GT
1980 Leather Sport RX-7
1980 Petty Targa RX-7 #11
1985 GSL-SE RX-7
1988 RX-7 10th Ann
1993 RX-7 VR Touring




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mwpayne


Hauling
Posts: 195
posted February 17, 2008 03:06 PM

Sounds good, maybe I could talk Klaus in to finding me a part number, if nothing else to compare.

       
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kansei


Redlining
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Posts: 423
posted February 17, 2008 03:58 PM
Edited By: kansei on 17 Feb 2008 15:59

Klaus may have them too, but...

1974 REPU Temperature Switch (backside of water pump housing) 1757-18-880

1974 REPU Water Thermo Switch (if equipped, on top of water outlet neck/thermostat housing) 1114-61-581

1974 REPU Thermosensor (on top of center housing) 1663-18-920

1981-1983 (maybe 1984/5 as well) RX-7 Temp Switch (backside of water pump housing) 8341-18-880

1981-1982 (maybe 1983/4/5 as well) RX-7 Thermo Switch (in bottom of radiator) 8182-18-970A (supercedes to N201-18-890)

Neal.

____________
Neal A.E. Swigert
Greenville, Michigan
1974 REPU Resto Project
1976 808 Wagon
1977 Cosmo
1978 Savanna RX-7 GT
1980 Leather Sport RX-7
1980 Petty Targa RX-7 #11
1985 GSL-SE RX-7
1988 RX-7 10th Ann
1993 RX-7 VR Touring




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mwpayne


Hauling
Posts: 195
posted February 17, 2008 07:13 PM

Thanks!

Wow, Neal, that's fantastic! I'm just used to Klaus having the parts lists..didn't know you did as well.
I'll call my mazda dealer first L O N G shot (but, I got lucky on the vent weatherstripping), then I'll try to come up with plan B, C, etc.
If I find a good part, I'll sure post the findings.

       
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kansei


Redlining
Wankelized
Posts: 423
posted February 21, 2008 02:51 PM

Good luck...

But you probably won't have any luck with anything other than the RX-7 parts.

Neal.

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mwpayne


Hauling
Posts: 195
posted February 22, 2008 05:16 PM

Bet you're right!

If I can find the time I'll call and find out tomorrow.

       
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Klaus44


Redlining
Posts: 365
posted February 22, 2008 06:11 PM

Have them try...

..the VIN#-specific parts search, if you can get them to do that. All I know is it's worked that way for certain parts in the past...

       
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