Stock Transmission Gauge Accuracy, or Lack Thereof? - Ford Powerstroke Diesel Forum
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Old 12-02-2008, 04:20 AM
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Stock Transmission Gauge Accuracy, or Lack Thereof?

Hey guys have a question I need to ask out of ignorance... I notice the OEM gauge on my truck, ('05, auto, totally stock) quickly, but smoothly, rises from cold to approximately halfway through the normal zone. From that point, no matter what I do, whether empty or towing upwards of 7000 pounds, it rides at that same point, never moving at all. I am assuming that it is a typical Ford "idiot light" in disguise as a gauge. I have seen several posts on here that describe it as not being very accurate as well.

My question, basically, is how this gauge operates? The probe, I assume is just a basic thermocouple. Does the PCM on the truck see a real, accurate temp? Does the PCM just output like a switch function, showing basic setpoints on the stock gauge, therefore the lack of accuracy?

I am not a big fan of accessories all over my truck, I prefer the stock look (ie. I dont want to have to put a 3-pillar gauge in my truck, I actually use the pull handle, LOL). Plus, nice, shiny electronic gadgets just attract that many more thieves.... However, I would like to know approximately what my tranny temps are when towing... I was looking at getting the Insight to use for gauges. It appears to plug into the OBD port to get everything but the EGT temps. If the PCM is seeing an accurate temp that the Insight can see, is there anyway to change the programming of the PCM using an SCT or other device to see a good temp on the stock guage? It's probably way more trouble that it's worth but I was just curious if it were a possibility.

to anyone who might could help clear up my confusion!
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Old 12-02-2008, 04:43 AM
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Your best bet is to get the Insight and know the true temps of your truck waiting to see that tranny light go past half you will already have a toasted tranny
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Old 12-02-2008, 01:24 PM
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The stock guage is nothing more than a analog idiot light. when it does move up its toast. get a aftermarket guage this is the only way to know the true temp.
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Old 12-02-2008, 01:30 PM
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you would be so surprised about that trans gauge. it warms up quickly to your eye, but actually takes the tranny a long time to warm up even in the summer time about 10 mins at that.....
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Old 12-02-2008, 02:13 PM
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The "Factory" transmission temp gauge is a glorified "idiot" light as its response is severly damped. Between 100-220F the needle will remain in the same position on the gauge. At 230F it will move up slightly to the middle of the normal range. At 250F it will move to Yellow.

The tow/haul light will flash at 275. The gage moves to red at 280. This is supported on page 36 of the OBDII Theory and Operations manual.
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Old 12-03-2008, 08:30 AM
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Thanks Bismic those were the numbers I was looking for!
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Old 12-03-2008, 08:35 AM
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you really never want it to go past 220, i believe thats when it starts breaking down the fuild. then it starts at seals and clutches
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Old 12-09-2008, 01:48 PM
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Quote:
Originally Posted by bismic View Post
The "Factory" transmission temp gauge is a glorified "idiot" light as its response is severly damped. Between 100-220F the needle will remain in the same position on the gauge. At 230F it will move up slightly to the middle of the normal range. At 250F it will move to Yellow.

The tow/haul light will flash at 275. The gage moves to red at 280. This is supported on page 36 of the OBDII Theory and Operations manual.
So, with all that said, is there anyway to buypass the PCM and plug the gauge "idiot light" into the trans temp output and make it a true gauge?
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Old 12-09-2008, 01:52 PM
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Originally Posted by cchase View Post
you really never want it to go past 220, i believe thats when it starts breaking down the fuild. then it starts at seals and clutches
Thanks, I was actualy wondering this earlier!
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Old 12-09-2008, 02:45 PM
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Originally Posted by big25country View Post
So, with all that said, is there anyway to buypass the PCM and plug the gauge "idiot light" into the trans temp output and make it a true gauge?
+1 --- I want the stock look but also like REAL guages..
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