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ECM temperature Vs. Temp gage

Discussion in 'The Garage' started by opfor2, Mar 12, 2006.

  1. opfor2

    opfor2 1/2 ton status

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    I'm trying to properly dial in my Flex-a-lite electric fan control box by using my OBD-1 scanner. The ECM temp would read 200* while the dash gage would read 230* which is right? I recently replaced the ECM temp sender unit so I'm wondering if because the ECM temp sender is on the intake and the temp gage is on the head that's why it's different. I'm going to trust the ECM over the gage but just wondering why the big difference. Any ideas ?

    Thanks

    Dan..
     
  2. Kiqman

    Kiqman 1/2 ton status

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    I have the same set up. I didn't plug into the ECM though. I set the fan all the way to the warmest position. Then I let the truck warm up to about 220. Then I adjusted the nob on the fan control until they kicked on. I turned the adjustment until the fans stopped once the dash gauge said about 210 again. Now they kick on at about 220 on their own and turn off at 210. If I'm putting around town I leave the switch in the cab "on" so they run constantly.
     
  3. HarryH3

    HarryH3 1 ton status Author

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    230 is pretty hot at the head. None of my factory gauges ever read more than 210 unless I'm dragging a LOT of weight behind in the middle of summer. They usually stay right around 190-200 in normal driving.
     
  4. opfor2

    opfor2 1/2 ton status

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    Normal driving the temp is at 195-200*. My question is that at idle and with a OBD-1 scanner connected to the ECM the two temp's don't jive. The ECM will read 200* while the dash temp gage will read 230*. So one of the two is not accurate. I'm betting on the gage sensor which I have never replaced on my stock 350. The ECM coolant sensor was recently replaced basically for ****'s and giggles.
     
  5. jarheadk5

    jarheadk5 1/2 ton status

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    When my K5 was still running, my temp gauge would occasionally peg itself on the high-side for no apparent reason. I'd have to bang on the face of the gauge a few times to get it to drop back to normal. For that reason, I'd trust ECM temp over the gauge, especially if you've recently replaced the sender.
     
  6. Chevy305

    Chevy305 6 Lug 14bsf Status Premium Member GMOTM Winner

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    I've noticed something similar to whats hapening with you on my truck. I have a mechanical temp gauge in the thermostat housing with a 160* therostat. My temp is off by about 15* or so. I know my gauge is accurate, but I think the front of the manifold is cooler than the temp in the head. I don't know but I think that might be what is happening.

    Try switching the placement of the sensors. then go from there.
     
  7. Thunder

    Thunder 3/4 ton status

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    Dont trust your factory Guage. They are notoriously inaccurate.Trust Your ECM. Or get a quality mechanical Guage.
     
  8. Russell

    Russell LB7 Tahoe Status Premium Member GMOTM Winner

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    Yep, the factory sending units for the gauges are not known for their accuracy, definitely trust the ECM's gauge, its far more precise.
     
  9. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    The problem you are having (chevy305) is that you have your temp sending unit installed on the cool side of the thermostat rather than the hot side where it should be. The only time you are reading the correct temp is the instant when the thermostat opens and allows the hot water to pass your sending unit on its way back to the radiator where it sits and cools until the cycle happens all over again. I doubt there is enough time for the gauge to read correctly before the thermostat closes again. You need to re-position the sending unit BEFORE the thermostat somewhere in the intake manifold so it can read the HOT temp or back into the driver side head where it really belongs.
     
  10. 4xcrazy

    4xcrazy 3/4 ton status

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  11. dyeager535

    dyeager535 1 ton status Premium Member

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    I was thinking about this, they should both be pretty close to the same temp regardless. One is right near the combustion chambers, but the other sees the combined temp from all of them. You aren't going to shed much heat by the time it gets there, and the coolant is coming up through the heads anyway to the front of the intake.

    I think it's a wash. There is something wrong if they are reading wildly different. Comparing with another gauge or a tool as pictured would confirm, but I'd go by the ECM one. GM thought the ECM one was enough to control the primary cooling fan on applications so equipped, so it would stand to reason that is the temperature to worry about, if you have to trust one of the two.

    Of course, if there is boiling right near the sender for some reason, that could skew readings as well.

    Keep in mind, you are dealing with a temperature guage (and sender?) that is no less than 15 years old, "crappy factory gauge" is not truth. Nor is any aftermarket gauge more accurate. Unless you have personally tested it against a known value, new doesn't mean good.
     
  12. HarryH3

    HarryH3 1 ton status Author

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    You're wecome to ruin your junk. I'll take care of mine (and recommend that others do the same with theirs). 230 degrees is getting pretty toasty. That's a temp that I wouldn't want to see for more than a few seconds. I know the NASCAR boys run that hot or hotter, but their engines barely last 500 miles (if they even make it that far). ;)

    If my junk is running at more than 210, in the summer, with the a/c on, pulling a long grade, I'm searching for the reason. :cool1:
     

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