Engine temp gauge is very low
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Senior User
Joined: Apr 2014
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From: SW Colorado
Engine temp gauge is very low
Gentlemen,
The engine temp gauge in my '90 C-350 (7.5L) reads very low (and was that way when I bought it last month). It seems that this is not an unusual problem as these trucks get older.
After a fair bit of research, I ordered a Motorcraft SW2328 replacement sensor. This has the "green" insulator, which matches what is already installed in the engine. I installed the new sensor today, but the behavior of the gauge remains the same.
I question the appropriateness of the SW2328 sensor. My cheapy VOM doesn't have enough resolution to indicate exactly what the resistance of the sensor is, but shows it to be somewhat on the high side. Judging from the gauge's behavior, that indication is justified.
So what is the correct sensor? The existing sensor has obviously been around for a while, and I assumed it to be original. However, upon removal today, it has Teflon tape wrapped around the threads, so somebody has been in here before. There is a pile of conflicting information out there about which sensor does what (the majority indicating that the SW2328 is correct).
Anybody know which one is actually correct?
Thanks!
The engine temp gauge in my '90 C-350 (7.5L) reads very low (and was that way when I bought it last month). It seems that this is not an unusual problem as these trucks get older.
After a fair bit of research, I ordered a Motorcraft SW2328 replacement sensor. This has the "green" insulator, which matches what is already installed in the engine. I installed the new sensor today, but the behavior of the gauge remains the same.
I question the appropriateness of the SW2328 sensor. My cheapy VOM doesn't have enough resolution to indicate exactly what the resistance of the sensor is, but shows it to be somewhat on the high side. Judging from the gauge's behavior, that indication is justified.
So what is the correct sensor? The existing sensor has obviously been around for a while, and I assumed it to be original. However, upon removal today, it has Teflon tape wrapped around the threads, so somebody has been in here before. There is a pile of conflicting information out there about which sensor does what (the majority indicating that the SW2328 is correct).
Anybody know which one is actually correct?
Thanks!
Logistics Pro
Joined: Jul 2009
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From: Lansdale, PA
The sensor for the gauge is the single prong one. Teflon tape isn't an issue unless you put so much on there it won't make contact with ground.
Your gauge itself could be "out of calibration". There's a little circuit board on the back of instrument cluster, it may control the temp, not sure though. It does fuel gauge and something else I think.
Your gauge itself could be "out of calibration". There's a little circuit board on the back of instrument cluster, it may control the temp, not sure though. It does fuel gauge and something else I think.
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From: SW Colorado
Yes.
Honest, I know what the problem is. I can elaborate on the troubleshooting exercise if desired, but what I really need is a part number for a sensor that somebody has actually installed that operates the gauge in the proper range.
The closest auto parts store is a long ways off so ohming out several isn't an option. and Rock-Auto and the actual auto parts stores don't seem to know for sure which sensor is the right one.
Honest, I know what the problem is. I can elaborate on the troubleshooting exercise if desired, but what I really need is a part number for a sensor that somebody has actually installed that operates the gauge in the proper range.
The closest auto parts store is a long ways off so ohming out several isn't an option. and Rock-Auto and the actual auto parts stores don't seem to know for sure which sensor is the right one.
Logistics Pro
Joined: Jul 2009
Posts: 3,635
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From: Lansdale, PA
Ummm
Well there's not too many variations of the gauge sensor from the 60s until 2000s. Like you said though, variation in the ohms from part to part is the issue.
If you want to tweak the needleto be in a different area of the gauge, put in a pot or a resistor. To alter the signal a little bit.
You have the correct motorcraft part number, why do you feel as though it's incorrect.
Well there's not too many variations of the gauge sensor from the 60s until 2000s. Like you said though, variation in the ohms from part to part is the issue.
If you want to tweak the needleto be in a different area of the gauge, put in a pot or a resistor. To alter the signal a little bit.
You have the correct motorcraft part number, why do you feel as though it's incorrect.
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Joined: Apr 2015
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From: Ft Bliss
my 90 460 always stayed really cold and heat didnt really work.. i opened up the thermostat housing to find out there was nothing there. trip to oreillys and back and i had a 195 thermostat and truck was on the 'o' on the gauge i believe and heat worked great after wards.
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From: SW Colorado
What is your basis for this statement? I have found lots of things that imply this, but none that are definitive. (I hope that doesn't read offensively, it's not intended to. 
) I've also found several sources that specifically say that the SW2328 is not the right part.
The details: the '90 F-350 EVTM book says the temp sensor resistance should be 74 ohms cold and 9.7 ohms hot. My not-high resolution VOM reads higher than that at perhaps 200 ohms cold and perhaps 100 ohms hot. The gauge itself reads perhaps an eighth-inch below the "C" when cold and moves up slightly to less than a sixteenth-inch below the "C" when hot. This is very much within the range of what I would expect with sensor resistance readings as posted above. Since the gauge also pegs out on the high end when the sensor wire is grounded, I have no reason yet to think the gauge is defective in any way. The other gauges all read within a range that does not raise any suspicion, and the fuel gauge reads above high when the tank is completely full so there is no reason to think the supply voltage at the gauges is incorrect.
I do not know that the SW2328 is the wrong sensor, but I have nothing that lets me rule it out.
) I've also found several sources that specifically say that the SW2328 is not the right part. The details: the '90 F-350 EVTM book says the temp sensor resistance should be 74 ohms cold and 9.7 ohms hot. My not-high resolution VOM reads higher than that at perhaps 200 ohms cold and perhaps 100 ohms hot. The gauge itself reads perhaps an eighth-inch below the "C" when cold and moves up slightly to less than a sixteenth-inch below the "C" when hot. This is very much within the range of what I would expect with sensor resistance readings as posted above. Since the gauge also pegs out on the high end when the sensor wire is grounded, I have no reason yet to think the gauge is defective in any way. The other gauges all read within a range that does not raise any suspicion, and the fuel gauge reads above high when the tank is completely full so there is no reason to think the supply voltage at the gauges is incorrect.
I do not know that the SW2328 is the wrong sensor, but I have nothing that lets me rule it out.
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Logistics Pro
Joined: Jul 2009
Posts: 3,635
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From: Lansdale, PA
I try not to give false information...
1990 Ford E-350 Econoline Engine Coolant Temperature Sender | FordParts.com
Granted that's not for a camper chassis, but it's for a van which typically the same as the camper/cutaway chassis.
The only other one listed is for a diesel.
I just looked at your signature, you have a centurion not a van, but I'm still sure sensor is the same across the board with the sender.
1990 Ford E-350 Econoline Engine Coolant Temperature Sender | FordParts.com
Granted that's not for a camper chassis, but it's for a van which typically the same as the camper/cutaway chassis.
The only other one listed is for a diesel.
I just looked at your signature, you have a centurion not a van, but I'm still sure sensor is the same across the board with the sender.
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From: SW Colorado
I have tried to use that website repeatedly to confirm parts, but with no luck. I'm not sure what I'm doing wrong. I've even given it the VIN.
Anyway, that is pretty much definitive. I can't imagine that a truck chassis would use anything different. Thank you for that.
So, I've got the correct sensor but the gauge reads very low. I wish more folks would post their findings once they resolve their problem. There are piles of threads referring to the exact same scenario but precious few identifying the solution. The one definitive post on the subject used the sensor with the black insulator rather than the green, but I have no idea what the difference is. I also found a sensor with a red insulator.
I think my next step should involve a much more precise VOM and, perhaps, a similar truck with a properly functioning gauge.
Anyway, that is pretty much definitive. I can't imagine that a truck chassis would use anything different. Thank you for that.
So, I've got the correct sensor but the gauge reads very low. I wish more folks would post their findings once they resolve their problem. There are piles of threads referring to the exact same scenario but precious few identifying the solution. The one definitive post on the subject used the sensor with the black insulator rather than the green, but I have no idea what the difference is. I also found a sensor with a red insulator.
I think my next step should involve a much more precise VOM and, perhaps, a similar truck with a properly functioning gauge.
Postmaster
Joined: Nov 2011
Posts: 3,533
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From: SW Florida
Can you get another meter to use? It don't sound like resolution is the problem. If you can get another meter then use for the test then also test the leads on your not-so-great meter to see if they've developed high resistance.
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From: SW Colorado
Well, it cost $10 at the local hardware store, way off the beaten path, so it's probably a $2 meter just marked up to cover the extra transportation. 
Actually, I don't think it's inaccurate but it has only a 1K ohm scale and the last 1K covers less than a half-inch of needle travel, so you're never going to be able to determine that last ten ohms!
I am going to have to find another meter.
Actually, I don't think it's inaccurate but it has only a 1K ohm scale and the last 1K covers less than a half-inch of needle travel, so you're never going to be able to determine that last ten ohms!
I am going to have to find another meter.
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From: SW Colorado
Or, perhaps, not.
So, I use my not-so-high resolution meter to check the functioning gauge in my '86 (also f-350 and 460). When cold, the sensor reads over 400 ohms and the gauge is as low as it will go. However, when hot, the gauge sits right at the "o" in "normal" and the sensor reads approximately 50 ohms.
And, guess what? With the SW2328 sensor, the gauge reads very low, just like it did in the '90. I'm back to the sensor as the problem, and with very good reason.
So, what's the deal with the SW2328? Beats the heck out of me. Either they are being made incorrectly, or Ford's information about the correctness of it for the application is wrong, or the sky turns green tomorrow, or? Considering that the truck had an (old) green insulatored part in it that has the exact same behavior and resistance values when I started, either the part has become wrong over the years, or it's been wrong all along. Is that part in there (remember the non-factory Teflon tape?) because somebody else already tried to fix this problem?
I think I'm starting to understand why so many of these trucks have temp gauges that read so low.
So, I use my not-so-high resolution meter to check the functioning gauge in my '86 (also f-350 and 460). When cold, the sensor reads over 400 ohms and the gauge is as low as it will go. However, when hot, the gauge sits right at the "o" in "normal" and the sensor reads approximately 50 ohms.
And, guess what? With the SW2328 sensor, the gauge reads very low, just like it did in the '90. I'm back to the sensor as the problem, and with very good reason.
So, what's the deal with the SW2328? Beats the heck out of me. Either they are being made incorrectly, or Ford's information about the correctness of it for the application is wrong, or the sky turns green tomorrow, or? Considering that the truck had an (old) green insulatored part in it that has the exact same behavior and resistance values when I started, either the part has become wrong over the years, or it's been wrong all along. Is that part in there (remember the non-factory Teflon tape?) because somebody else already tried to fix this problem?
I think I'm starting to understand why so many of these trucks have temp gauges that read so low.
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From: SW Colorado
Problem Resolved
So, following the rules of etiquette , I'm posting on how this problem was resolved.
I had no luck with sensors of any type and figured the thermostat had to rank high on the possible problems. The entire truck looks unmolested, including the thermostat housing and, indeed, it had never been apart. The original thermostat is some sort of thing I've never seen before, but does have a Ford part number starting with "E8". It now has a NAPA 195 degree thermostat, and the temp gauge goes up to the "O" in "NORMAL" now so it's happy days for a while.
The following are photos of the strange thermostat:
, I'm posting on how this problem was resolved.I had no luck with sensors of any type and figured the thermostat had to rank high on the possible problems. The entire truck looks unmolested, including the thermostat housing and, indeed, it had never been apart. The original thermostat is some sort of thing I've never seen before, but does have a Ford part number starting with "E8". It now has a NAPA 195 degree thermostat, and the temp gauge goes up to the "O" in "NORMAL" now so it's happy days for a while.
The following are photos of the strange thermostat:
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