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Discussion Starter · #1 ·
The temperature gauge, on my 88 bronco with a 351, reads below the minimum line even after running for hours. I tried grounding out the single wire On both of the two engine temp sensors and the gauge did not jump to max or even move the needle the slightest. I replaced the ECT sensor with two wires aswell and this did not seem to have any affect either. The needle on the temp gauge does move slightly on rare occasions from under the minimum line to right at the minimum line. I do not know what causes it to move. Based on my tests and there being no trouble codes I think my gauge is bad or failing. My question is how do I fix the gauge or am I completely overlooking something important.

Additionally, I can measure roughly 5v coming from the single wire boot that attaches to each of the engine temperature sensors. If that helps at all.
 
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Discussion Starter · #3 ·

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1996 Bronco XLT 5.8L
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Old expression to bump a thread to the top for exposure. Also an indication that I'm I retested in the answer and throws it on my list of threads I've replied to.

Sent from my Pixel 3 XL using Tapatalk
 

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The temperature gauge, on my 88 bronco with a 351, reads below the minimum line even after running for hours. I tried grounding out the single wire On both of the two engine temp sensors and the gauge did not jump to max or even move the needle the slightest. I replaced the ECT sensor with two wires aswell and this did not seem to have any affect either. The needle on the temp gauge does move slightly on rare occasions from under the minimum line to right at the minimum line. I do not know what causes it to move. Based on my tests and there being no trouble codes I think my gauge is bad or failing. My question is how do I fix the gauge or am I completely overlooking something important.

Additionally, I can measure roughly 5v coming from the single wire boot that attaches to each of the engine temperature sensors. If that helps at all.
If this isn't an electronic issue It is possible your thermostat has gone bad, and could be stuck in the "full open" position? That would cause water to flow through your engine constantly and never allow the engine to get up to operating temp. A 195 degree thermostat should keep the temp toward the center of the gage. Even a 180 degree would keep it in the bottom quarter of the gage.

Just my .02
 

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Discussion Starter · #6 ·
If this isn't an electronic issue It is possible your thermostat has gone bad, and could be stuck in the "full open" position? That would cause water to flow through your engine constantly and never allow the engine to get up to operating temp. A 195 degree thermostat should keep the temp toward the center of the gage. Even a 180 degree would keep it in the bottom quarter of the gage.

Just my .02
I appreciate your .02. Unfortunately I think if it was thermostat, the gauge would still work when I ground the sensors but it doesn’t then either.
 

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96 5.8, 4.10 gears with truetrac 4 inch lift, 15x10 with 35s, 50 series flow master, 3 inch catback.
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Mine is a 96 but when this happened to me I bought a new gauge but the wrong one. When I went to put it back together I noticed a little corrosion on the connector pins. Cleaned that up and my gauge was working again. Just a possibility but it is one thing to check. Good luck.
 

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Discussion Starter · #8 ·
Mine is a 96 but when this happened to me I bought a new gauge but the wrong one. When I went to put it back together I noticed a little corrosion on the connector pins. Cleaned that up and my gauge was working again. Just a possibility but it is one thing to check. Good luck.
I bought an auxiliary temp gauge that I am mounting on an accessory panel. Unfortunately I can’t replace just the temperature gauge that’s built into the vehicle because the gauge cluster is one piece. I am still trying to understand why the built in gauge does not work. I traced the wire from the sensor and did not see any corrosion but may have missed something.
 

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96 5.8, 4.10 gears with truetrac 4 inch lift, 15x10 with 35s, 50 series flow master, 3 inch catback.
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Agree that just replacing the gauge itself for you isn't in the cards but was only thinking that if you check and clean the connections on the back of your temp gauge on the cluster and maybe make better contact by doing so that could possibly be a fix.
 

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Discussion Starter · #10 ·
I’ll continue to scour over those connections for corrosion. Very high chance there’s some tiny speck somewhere in there that’s throwing off the whole set up.
 

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Did a little hunting on this. I would swap the thermostat. I literally have the same issue as you. Just started this week. This weekend I'm gonna replace it. It's pretty cheap. Will keep you posted.
 

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Discussion Starter · #12 ·
Did a little hunting on this. I would swap the thermostat. I literally have the same issue as you. Just started this week. This weekend I'm gonna replace it. It's pretty cheap. Will keep you posted.
I replaced thermostat less than a couple hours of engine run time before now. If it works for you please let me know.
 

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88 351/AOD/4” ProComp 94 351/E4OD/4” Superlift
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The sender unit for the gauge is the single wire one on the drivers side of the engine. The ECT is for the EEC so it can adjust the air-to-fuel ratio. If nothing changes when you ground the sender wire straight then I would suspect the gauge.
 

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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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You CAN replace just the temp gauge and what ever one is vertically paired with it. The instrument cluster has 3 panels usually, sometimes 4 if you have a tach. Or you can replace the whole cluster.

Im betting its the sender or a bad connection.

The gauges after 87 are just idiot lights with needles. It gets a voltage range, and tells you if the temp is low, high, or ok. There is no way for them to tell you if its 185° or 225. If temp is normal, it could be wherever in the normal range, whether 185 or 205, the needle will point in generally the same spot. It wont show hotter unless you reach the temp at which it declares as too hot.
 
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