Gauge issues - ICVR issue?
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Mountain Pass
Joined: Mar 2022
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Gauge issues - ICVR issue?
Hi all,
my water temperature and oil pressure gauge are reading low. The resistance at the sender and also with the wiring make sense but the reading is too low. E.g. with the engine warmed up the gauge shows L. The oil pressure reading with a mechanical gauge is 50 psi and the cluster gauge shows 20 psi. Not sure about the fuel gauge, but I assume it is the same issue.
I suspect that the ICVR is the issue and produces not enough volt for an accurate reading. The gauges are very sensitive to the voltage. I don't have an oscilloscope handy to check the ICVR, but it is definitely pulsing the voltage.
Can anybody confirm my thoughts? What are the experiences with aftermarket ICVRs? I guess they are now solid state and not mechanical switches anymore.
my water temperature and oil pressure gauge are reading low. The resistance at the sender and also with the wiring make sense but the reading is too low. E.g. with the engine warmed up the gauge shows L. The oil pressure reading with a mechanical gauge is 50 psi and the cluster gauge shows 20 psi. Not sure about the fuel gauge, but I assume it is the same issue.
I suspect that the ICVR is the issue and produces not enough volt for an accurate reading. The gauges are very sensitive to the voltage. I don't have an oscilloscope handy to check the ICVR, but it is definitely pulsing the voltage.
Can anybody confirm my thoughts? What are the experiences with aftermarket ICVRs? I guess they are now solid state and not mechanical switches anymore.
Logistics Pro
Joined: May 2015
Posts: 4,474
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From: Tri Cities, TN
Here is a copy and paste from an old post I made. You cannot test the senders with an ohm meter. If you have more than one gauge with the same problem, it is likely the ICVR. Using the resistors is the fastest and quickest way to trouble shoot the gauges. Most of the oil senders out there are not correct for our 80 psi gauges and will not give a correct reading. The Autolite SW383 is the correct sender they are nearly extinct they have a stylized KS on them because they were made by King Seely and are stamped 80. You need to get a 10-ohm and a 73-ohm resistor.
The best way to test the gauges is to use a 10 ohm and a 73 ohm resistor. These King Seeley type gauges just measure resistance to ground at a nominal 5 volts. It makes no difference whether it is fuel, oil pressure or temperature they all work the same.
Disconnect the sender and connect the 10 ohm resistor to ground in place of the sender. The gauge should read to the high mark. Connect the 73 ohm resistor the same way and the gauge should read to the low mark.
If the gauge passes the test the sender is bad. And if it doesn't and the other gauges are working you need to trace the wiring.
You should never ground the sender wire to see if the gauge is working because if the ICVR has gone bad and is putting out 12 volts you can ruin the gauge. Actually on later models with printed circuit instrument wiring you can burn out the entire printed circuit .
The best way to test the gauges is to use a 10 ohm and a 73 ohm resistor. These King Seeley type gauges just measure resistance to ground at a nominal 5 volts. It makes no difference whether it is fuel, oil pressure or temperature they all work the same.
Disconnect the sender and connect the 10 ohm resistor to ground in place of the sender. The gauge should read to the high mark. Connect the 73 ohm resistor the same way and the gauge should read to the low mark.
If the gauge passes the test the sender is bad. And if it doesn't and the other gauges are working you need to trace the wiring.
You should never ground the sender wire to see if the gauge is working because if the ICVR has gone bad and is putting out 12 volts you can ruin the gauge. Actually on later models with printed circuit instrument wiring you can burn out the entire printed circuit .
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Mountain Pass
Joined: Mar 2022
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Thanks @Crop Duster !
I connected several resistors between GND and the sender wire. Here are the results:
Resistor in Ohm | Temp Gauge reading
72 | Slightly above C
30 | Slightly above the Low Line
20 | Center
15 | Slightly below High Line
10 | Slightly below H
I found a table for Ford temperature senders:
Ohm | Temperature | Reading
78 | 130 | C
50 | 160 | Low Line
26 | 200 | Center
16 | 230 | High Line
10 | 250 | H
I also checked the sender before installation by holding the sender in almost boiling water (maybe 205F) and measuring the resistance to 35 Ohm.
For the oil pressure I measured with 72 Ohm (~3 PSI reading) and 10 Ohm (80+ PSI).
My conclusion, please comment.
I connected several resistors between GND and the sender wire. Here are the results:
Resistor in Ohm | Temp Gauge reading
72 | Slightly above C
30 | Slightly above the Low Line
20 | Center
15 | Slightly below High Line
10 | Slightly below H
I found a table for Ford temperature senders:
Ohm | Temperature | Reading
78 | 130 | C
50 | 160 | Low Line
26 | 200 | Center
16 | 230 | High Line
10 | 250 | H
I also checked the sender before installation by holding the sender in almost boiling water (maybe 205F) and measuring the resistance to 35 Ohm.
For the oil pressure I measured with 72 Ohm (~3 PSI reading) and 10 Ohm (80+ PSI).
My conclusion, please comment.
- The ICVR is ok.
- My gauge readings are within what I can expect with external resistors attached.
- The resistance of the sender is too high, leading to lower readings (e.g. 35 Ohms at 205ish F). According to the table 200F should be 26 Ohm.
- My engine is running at a good temperature (somewhere between 190 and 205F), but my reading at the gauge is close to the low line which would indicate ~170F. I plan to verify the engine temperature with an IR gun this weekend.
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