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Coolant temp dash light by Rsvl-Rider
Started on: 05-21-2020 02:06 AM
Replies: 5 (108 views)
Last post by: olejoedad on 05-24-2020 12:01 PM
Rsvl-Rider
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Report this Post05-21-2020 02:06 AM Click Here to See the Profile for Rsvl-RiderSend a Private Message to Rsvl-RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
1988 Iron Duke, auto, no AC.

Recently the engine temp warning light has started coming on. Jenny says sometimes it glows weakly and sometimes it goes fully bright.

I let the engine idle for a while. Once the engine warms up the gauge still seems to read normally and then the light comes on. Soon after that the radiator fan kicks on and I can see the gauge needle drop a bit and then the light goes out. I replaced the thermostat with a brand new Stant 195* and that had no effect. The temp gauge seems to read normally so I suspect the problem is in the switch that turns on the warning light, but I'm not sure and I'm not clear on which one it is. Is the coolant temperature sensor that is installed in the thermostat housing the one that drives the warning light?

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phonedawgz
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Report this Post05-21-2020 04:18 AM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
The gauge/light sender looks like the one on the right in this picture.


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theogre
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Report this Post05-21-2020 04:38 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Do Not trust the dash gauge.

Light switch or wiring could be iffy but need to check engine temp.

Use ECM scan tool or whatever to read Engine temp.
ECT for ECM has correct Ω at some temps in my Cave, Sensors Quick Ref
or try IR thermometer or related but IR lools maybe hard to find w/ CCPvirus panic.
K type thermalcouple w/ meter that reads them work too.
cheap electro "meat" or "candy" thermo work too.
Measure temp at base of Tstant tube next to head.

ETA ↓
if using small tips for thermocouple etc for reading engine, use a small blob of brake or wheel bearing grease. Both won't run and transfer heat to tip better.

Engine w/ trapped air or crush pipes are good ways to overheat.
See my Cave, Radiator Caps and rest of section.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)


The Ogre's Fiero Cave

[This message has been edited by theogre (edited 05-21-2020).]

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Rsvl-Rider
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Report this Post05-24-2020 03:09 AM Click Here to See the Profile for Rsvl-RiderSend a Private Message to Rsvl-RiderEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by theogre:

Do Not trust the dash gauge.

Light switch or wiring could be iffy but need to check engine temp.

Use ECM scan tool or whatever to read Engine temp.
ECT for ECM has correct Ω at some temps in my Cave, Sensors Quick Ref
or try IR thermometer or related but IR lools maybe hard to find w/ CCPvirus panic.
K type thermalcouple w/ meter that reads them work too.
cheap electro "meat" or "candy" thermo work too.
Measure temp at base of Tstant tube next to head.



 
quote
Originally posted by phonedawgz:

The gauge/light sender looks like the one on the right in this picture.



So I borrowed an infrared thermometer and took readings at the base of the thermostat housing. The readout confirmed the temp gauge so I guess that means the warning light was wrong (even though it did not come on again during this latest test). As I understand it the same sensor / sender drives both the warning light and the gauge so either way this seems to confirm that it needs to be replaced, is that right?
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Gall757
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Report this Post05-24-2020 10:52 AM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
As the sensor is relatively cheap, its probably the thing to do, but the connector and wires are often damaged and the real problem. Don't let the auto parts store sell you the wrong sensor.
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olejoedad
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Report this Post05-24-2020 12:01 PM Click Here to See the Profile for olejoedadClick Here to Email olejoedadSend a Private Message to olejoedadEdit/Delete MessageReply w/QuoteDirect Link to This Post
I would disconnect the gage/light plug from the sensor and check the light circuit for shorts to ground before I replaced the sensor.

The light should come on full bright when the sensor closes the thermal switch, not just dimly glow.
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