D_Bomb17 Posted April 24, 2018 Share Posted April 24, 2018 Hi all, About a month ago, the coolant gauge in my 99 Pathy started acting weird. Examples include jumping to running temperature at startup, dropping to cold, spiking to hot before settling at running temp. One day on my way home from work it started at running temp (after sitting for 8 hours), spiked to hot about 3 minutes into my drive, dropped to cold 2 minutes later, rose to running temp like normal, then spiked to hot again just before i got home. Just this last week it has started to be somewhat normal except for spiking to hot and staying there about 5 minutes into my drive. Replacing the sensor located at the upper rad hose didn't do anything to fix the problem (maybe that's the wrong sensor?). A mechanic friend suggested it could be the thermostat not opening properly so we replaced that as well. Still no change. After doing a bit of research i can only come up with a few things that might be the problem: - bad replacement sensor - plugged radiator - sensor grounding out - water pump is on its way out. Any one have any idea whats going on, or have had this before? Any input on how to proceed is much appreciated. Cheers, DN Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 25, 2018 Share Posted April 25, 2018 No fault with the cooling would make the temp jump to operating temp at startup after sitting eight hours. This sounds like an electrical fault. If it's not the sensor, I'd be suspicious of the wiring between the sensor and the dash. I'd expect it to only spike hot or only spike cold with a wiring issue, though; spiking both ways makes me wonder if the gauge itself might have something wrong with it. I'd still start by checking the wiring to rule it out. One test you could do is to figure out what resistance the sensor should have when the engine's at operating temp. Warm up the truck, unplug the sensor, test from the connector to ground. Then the next time it reads cold or hot when it should be at operating temp, pull over and check it again. If the sensor reading is more or less the same, you know the sensor's not the problem. Also make sure you changed the right sensor. If yours is like my WD21 (and I'm pretty sure it is), it'll have two coolant temp sensors right next to each other. The 2-wire is for the computer, the 1-wire is for the dash gauge. Link to comment Share on other sites More sharing options...
D_Bomb17 Posted April 25, 2018 Author Share Posted April 25, 2018 Mine only has the 1-wire in that location, whereas my 93 has both together. Not sure where the other one would be? However, I checked the sensor with my multimeter, and its reading correctly. Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 25, 2018 Share Posted April 25, 2018 I'm seeing both types on Rockauto for the '99, but the service manual just points to the general vicinity of the upper coolant neck. If the one-wire tests good, though, then it sounds like you've replaced the right one and the problem is between its plug and the dash. Link to comment Share on other sites More sharing options...
D_Bomb17 Posted April 25, 2018 Author Share Posted April 25, 2018 Thanks for the help Slartibartfast! I am heading to the local pick-a-part to pick up a new instrument panel Link to comment Share on other sites More sharing options...
ferrariowner123 Posted April 25, 2018 Share Posted April 25, 2018 I had issues similar to this on my 96, however, it was my tacho that was jumping around like crazy. all i did to fix it was re-solder the connections on the back of the tachometer assembly (you need to disassemble the cluster to get access to the solder connections). Not sure if this can be done on the fuel or coolant gauge, but i can confirm and faulty connection has caused similar issues on mine. -Kyle 1 Link to comment Share on other sites More sharing options...
D_Bomb17 Posted May 4, 2018 Author Share Posted May 4, 2018 UPDATE: I noticed that my radiator had a small crack in the top, plus about a third of the neck where the upper rad hose connects to was broken off. A new rad was put in but it didn't do anything for the coolant temp gauge. I didn't have time to go to the local pick-a-part the other day, but i did a continuity test as directed in the FSM. I didn't get continuity, but figured it might be because the probe wasn't making contact properly inside the harness, so i shoved it in deeper. Doing that either cleaned or opened the connection enough for the wires to make contact with the sensor, because the gauge is working properly now lol At least my entire coolant system is upgraded haha! Thanks for the suggestions guys! -Dennis 2 Link to comment Share on other sites More sharing options...
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