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Temp guage inaccuracy???

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Old 12-17-03, 12:59 AM
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Question Temp guage inaccuracy???

I have come across many sites that say that the coolant temp guage in the FD is not very good. When it reads the the car is overheating it is usualy to late. Im not quite shur what they mean by to late, i supose for coolant o ring problems.

But my question is, Is there an upgrade for the coolant temp switch that will go in the stock location and will hook up to the stock guage making it more accurate?

Just to eliminate the need to add another coolant tem guage.

Thanks

PS i have already done a search but did not find what i was looking for.
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Old 12-17-03, 01:39 AM
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Check out the San Diego RX-7 Club website:
http://www.geocities.com/sdrx7_club/technical.html
They have a detailed how-to on linearizing the stock gauge.
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Old 12-17-03, 01:45 AM
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Thanks alot for that link. Its a real help because i would like to keep the number of guages i require to a minimum for now.

Thanks again
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Old 12-17-03, 01:47 AM
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http://www.iluvmyrx7.com/3rdgen/how-...auge%20mod.pdf

haven't tried it, but i plan to.

also, they mean to late as in it takes so long for the high temps to register with the temp gauge, that if you don't pull over instantly, or even if you do, serious damage probably has already occured...and yes, likely to your o rings

also, if u mean just putting a new guage in the stock location...
http://www.maxcooper.com/rx7/how-to/spa_gauges/
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Old 12-17-03, 08:45 AM
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I wish there was somthing like 89Turbo944 was talking about, just a sensor swap or something, as that linerizing of the gauge itself seems like a TOTAL PITA.
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Old 12-17-03, 09:02 AM
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A sensor swap won't work unless you're also adding a different gauge. The problem is the stock gauge isn't linear...the "normal" reading on the gauge can mean any of a wide range of temperatures, many of which are bad.

jds
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Old 12-17-03, 09:34 AM
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I understand, just seems like a PITA to do. I think it would be easier to add a new gauge than to take apart your dash and solder on all that crap.
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Old 12-17-03, 10:01 AM
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FYI,

the first 12 months I owned my car I had extensive cooling problems. Among others, the following things happen to cause me to "over heat" on more than one occasion.

1) upper rad hose exploded.
2) my drivers side radiator fan died 2 times (koyo core rubbed it)
3) my wiring for my fans cracked the rubber sheath causing the wire to touch the chassis making the fuse that runs the fans blow, so both fans stop.
4) the hose behind the manifold decided to crack.
5) my AST cracked the nipple off. I drove and over heated.

My water temps hit has high as 114-117C. FYI, the stock gauge doesn't start to move until about 115-116C.

When I cracked my apex seal some time later my mechanic took apart my engine to rebuild it. We found the O-Ring to be fine. The gauge on these occasions read just below the red line... It never made it in to the red, but got close.

I agree the stock gauge has issues and that when the gauge starts to move you have seconds to react, but I also believe that as long as the needle doesn't go into the red, your car will not be damaged.

I also beleive that while the car can operate fine even in temps of 114-116C, doing that on a regular basis will cause the O-ring and other engine componenets to become brittle OVER TIME.

Just my experience.
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Old 12-17-03, 10:02 AM
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I decided to go down a similar path as Max Cooper, but using AutoMeter gauges

https://www.rx7club.com/photo/showphoto.php?photo=4400

more info in this thread:
https://www.rx7club.com/forum/showth...hreadid=199139


Last edited by maxpesce; 12-17-03 at 10:09 AM.
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Old 12-17-03, 10:35 AM
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Re: Temp guage inaccuracy???

Originally posted by 89Turbo944
... But my question is, Is there an upgrade for the coolant temp switch that will go in the stock location and will hook up to the stock guage making it more accurate?

Just to eliminate the need to add another coolant tem guage.

I didn't want/need to do the linearization, so I just added a resistor in parallel to the gage sensor. My gage will now start rising when ecu 1st turns fans on, at 221F. Before it would not rise 'till about 240+F. Only drawback is it indicates 'normal' to soon aft start-up, so I just wait a bit before considering it warmed up.
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Old 12-17-03, 11:13 AM
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Re: Re: Temp guage inaccuracy???

Originally posted by KevinK2
I didn't want/need to do the linearization, so I just added a resistor in parallel to the gage sensor. My gage will now start rising when ecu 1st turns fans on, at 221F. Before it would not rise 'till about 240+F. Only drawback is it indicates 'normal' to soon aft start-up, so I just wait a bit before considering it warmed up.
Kevin, can you give us more details? What size resistor? You say that it starts moving when the ECU turns on the fans, but how high does it rise before it goes back down to the normal range (when ecu turns off the fans).
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Old 12-17-03, 11:19 AM
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Thanks for the useful info guys. I think i will go for the liniar conversion thingy. I would like to keep the guages as stock as possible.

This allows me to get a set of white aftermarket guage faces that fit properly.

Thanks again.
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Old 12-17-03, 11:50 AM
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Re: Re: Re: Temp guage inaccuracy???

Originally posted by novadan67
Kevin, can you give us more details? What size resistor? You say that it starts moving when the ECU turns on the fans, but how high does it rise before it goes back down to the normal range (when ecu turns off the fans).
I use parking lites in traffic, to keep temps below 210 at all times (some use pfc or miata switch to do same), so I've yet to see it rise above normal. I test it by sitting at idle until fans 1st come on. By 230F you would see about 1/4" rise. Any motion for me would mean take corrective action immediately. Main use for me is at track events, where I will back off if I see it budge (usually don't have to).

resistor is wired with combo male/female spade at sensor end for oem female to connect to. other end is grounded. i'll try to measure it tonite and post value.
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