Automotive

[BrimStone]

I have a 2001 Ford Ranger, 4 cylinder, 2.5 liter engine with over 180,000 miles, it runs great and its in mint condition.  This engine has 2 coolant sensors in the front of the engine.  One sends info to the computer, the other to the dash gauge.  A couple of months ago, the dash gauge stopped registering any coolant temp.  I had this happen a few years ago, and replaced the sensor and it fixed the problem.  So I bought another sensor and sealant tape but this new sensor didn't fix the problem.  I brought the sensor back, told the guy it doesn't work, and I got it replaced. But the 2nd one didn't fix the problem either.  The engine is VERY clean and the wiring at the connectors doesn't feel broken or frayed.  Just recently, I accidently found a way to get the sensor to work for a short period of time. I was hosing off the engine (I went out in the woods and hit some big mud puddles) and later that same day went to the store.  The engine was still a little wet and I noticed the coolant temp gauge on my dash is now registering the coolant temp!  15 or 20 min later, the dash gauge stopped working.  I can duplicate this temporary "fix" just by hosing down the engine compartment.  I have checked different connectors, including the big one at the firewall.  I have an Actron Scanner CP9180 and I keep it connected to keep on eye on the coolant temp.

Water is a terrible conductor for a DC electrical system and it should not fix the coolant sensor problem.  This seems like a simple fix but I am stumped.  Any ideas why hosing down the engine will temporarily "fix" my coolant sensor?

Thanks

Chris

[AAAPete]

Chris, kudos for the great detail in information! You hit the nail on the with water and its conductive properties. If all the connectors are good, clean and tight it could be a harness issue. I would do a couple things. I would first separate each connector, one by one for a detailed inspection. I would be looking for any signs of corrosion on the terminals and/or on the spades. I would also look for any terminal spades that are not pushed all the way through the connector. When reconnecting the connector look on the back side of the connector that has the spades and see it any of the wires move outward. The connector may be locking shut but the spade may be being pushed outward and not making a good connection. Next I would hunt down all ground wires in the engine bay especially where you are concentrating the water spray. A bad ground can manifest itself in unusual ways. Next if the problem isn' t found I would look at the wires from the sender all the way back to the firewall. This will require opening the conduit for the harness. Look for wires with deteriorated insulation and corrosion. Corrosion can wick through a wires for several inches.

It sounds like you are on the right track and I am confident you will find the source of this intermittent hair puller!