Car RamRod Posted December 12, 2007 Share Posted December 12, 2007 I got my engine running the other day, and everything is gravy, minus the engine temperature gauge in the cluster. When I start the truck it goes straight up to the max. I changed the CTS out today and it didn't help. All of my other gauges work. Any thoughts? Matt Link to comment Share on other sites More sharing options...
offroader461 Posted December 12, 2007 Share Posted December 12, 2007 mine in my XJ does the same thing when the key doesnt release all they way back....does you radio work? if it does then you might have a short in the CTS wiring somewhere. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted December 12, 2007 Share Posted December 12, 2007 faulty gauge. happened to my oil pressure gauge after the dash swap...installed another opg and now it works just fine. also had this issue with the batt. gauge. these are 20 year old trucks, the gauges aren't that accurate to begin with, and failure happens...I'd say it's your best bet. Link to comment Share on other sites More sharing options...
offroader461 Posted December 12, 2007 Share Posted December 12, 2007 faulty gauge. happened to my oil pressure gauge after the dash swap...installed another opg and now it works just fine. also had this issue with the batt. gauge. these are 20 year old trucks, the gauges aren't that accurate to begin with, and failure happens...I'd say it's your best bet. that too :D Link to comment Share on other sites More sharing options...
1986Comanche Posted December 12, 2007 Share Posted December 12, 2007 I got my engine running the other day, and everything is gravy, minus the engine temperature gauge in the cluster. When I start the truck it goes straight up to the max. I changed the CTS out today and it didn't help. All of my other gauges work. Any thoughts? Matt I would say most likely the temp gauge is bad. Like JeepcoMJ has said some of these trucks are over 20 years old now and it wouldn't surprise me if the gauge is bad. Link to comment Share on other sites More sharing options...
Car RamRod Posted December 12, 2007 Author Share Posted December 12, 2007 mine in my XJ does the same thing when the key doesnt release all they way back I'm gonna try this, because the ign. cylinder is pretty sticky. I don't have a radio in so I don't know about that. As for the cluster, I just picked this one up in the classified section so I'm not sure if it was working beforehand. I'll let you guys know how it works out. Thank for the help, Matt Link to comment Share on other sites More sharing options...
Eagle Posted December 12, 2007 Share Posted December 12, 2007 Which coolant temp sensor did you replace? If your MJ is a 90 or earlier, there are two. The one on the side of the block supplies input to the ECU but not to the gauges. The one for the gauge is the one in the rear left corner of the head. Could also be a bad wire. If the wire is shorted it'll go all the way to one side of the gauge, if it's an open circuit it'll go to the other side. Don't remember which way, though. Link to comment Share on other sites More sharing options...
Car RamRod Posted December 12, 2007 Author Share Posted December 12, 2007 Which coolant temp sensor did you replace? If your MJ is a 90 or earlier, there are two. The one on the side of the block supplies input to the ECU but not to the gauges. The one for the gauge is the one in the rear left corner of the head. Could also be a bad wire. If the wire is shorted it'll go all the way to one side of the gauge, if it's an open circuit it'll go to the other side. Don't remember which way, though. I changed the on the block. Any way I could test the top one before buying a new one? Matt Link to comment Share on other sites More sharing options...
Car RamRod Posted December 13, 2007 Author Share Posted December 13, 2007 here's what I got so far.....when the cts on the head is unplugged, the gauge goes all the way down. When I plug it on, the needle shoots up to the top. To top it all off, the trucks overheating; I'm getting 205 in the resevoir tank with a lot of pressure, and 205 at the waterneck. The rest of the engine and radiotor ends are cooler, around 170. Any thoughts? Link to comment Share on other sites More sharing options...
Oizarod115 Posted December 13, 2007 Share Posted December 13, 2007 here's what I got so far.....when the cts on the head is unplugged, the gauge goes all the way down. When I plug it on, the needle shoots up to the top. To top it all off, the trucks overheating; I'm getting 205 in the resevoir tank with a lot of pressure, and 205 at the waterneck. The rest of the engine and radiotor ends are cooler, around 170. Any thoughts? 205 is NOT overheating... 210 is normal for a 4.0 and that means the gauge is fine, sending unit is bad most of our sensors work on a "resistance-to-ground" so they'll offer different resistances at different temps, so with it plugged in its got no resistance to ground when you take it out it thinks it has infinite resistance to ground. hence the gauge going to the extremes when plugged in and not plugged in Link to comment Share on other sites More sharing options...
offroader461 Posted December 13, 2007 Share Posted December 13, 2007 yea 205 is not bad at all...if you have a 195* thermostat with it open its not going to drop below 200*....my MJ runs at 205* at idle all day and no problems what so ever...my XJ runs the same..both have open cooling systems Link to comment Share on other sites More sharing options...
Car RamRod Posted December 13, 2007 Author Share Posted December 13, 2007 o ok. That's good news then. I am getting a lot of air pressure in the tank. Do I just need to burp the system? If so, whats the best way? Link to comment Share on other sites More sharing options...
Oizarod115 Posted December 13, 2007 Share Posted December 13, 2007 o ok. That's good news then. I am getting a lot of air pressure in the tank. Do I just need to burp the system? If so, whats the best way? it should be fairly pressurized compared to an open system. i think it runs at like 19psi or somethin IIRC Link to comment Share on other sites More sharing options...
Eagle Posted December 13, 2007 Share Posted December 13, 2007 here's what I got so far.....when the cts on the head is unplugged, the gauge goes all the way down. When I plug it on, the needle shoots up to the top. To top it all off, the trucks overheating; I'm getting 205 in the resevoir tank with a lot of pressure, and 205 at the waterneck. The rest of the engine and radiotor ends are cooler, around 170. Any thoughts? For starters, you are NOT overheating. The normal temperature for a 4.0L is 210 degrees. You did the plug and unplug deal and the gauge responded, so it's not totally fubar. Inless you have some resistors that you can use to test the range of the gauge, the next thing would be to replace the sender in the head. Wait -- there is another test you can run. The gauge is basically an ohmmeter. The temp sender for the 88 has a range of 0 to 88 ohms. I think it's zero when cold and 88 to max out the needle on the gauge. So you can use a multimeter to check what the sender is sending. Connect one lead to the head, and touch the other lead to the tip of the sender, where the wire pushes on. When the engine is cold it should read close to zero. At normal operating temperature, it should be in the area of 42 to 45 ohms. Link to comment Share on other sites More sharing options...
Car RamRod Posted December 13, 2007 Author Share Posted December 13, 2007 The gauge is basically an ohmmeter. The temp sender for the 88 has a range of 0 to 88 ohms. I think it's zero when cold and 88 to max out the needle on the gauge. So you can use a multimeter to check what the sender is sending. Connect one lead to the head, and touch the other lead to the tip of the sender, where the wire pushes on. When the engine is cold it should read close to zero. At normal operating temperature, it should be in the area of 42 to 45 ohms. ah great...thanks. I'll give that a shot when I get home. Matt Link to comment Share on other sites More sharing options...
Eagle Posted December 13, 2007 Share Posted December 13, 2007 Keep in mind what other guys told you. On the 88 that plastic coolant bottle is NOT an "overflow" bottle. It is an integral part of the cooling system, coolant flows through it, and it is under pressure. do NOT remove that cap when the system is hot and under pressure. Link to comment Share on other sites More sharing options...
1987Comanche Posted December 13, 2007 Share Posted December 13, 2007 Not to hijack your thread but I’m having a very strange coolant temp gauge issue at the moment too. The gauge originally worked ok but was very active, it would bounce between ¼ and ½ and twitch around all the time. In July the gauge finally gave out and would spin wildly about, to the point where it would go 360 around and look like a propeller. I figured the gauge was shot. Last weekend I finally got around to putting my new CD player in the Jeep (thanks Santa!) and, while I was there, I pulled the cluster and replaced it with the spare that came with the truck. The new gauge doesn’t bounce wildly but doesn’t work correctly either. It won’t move until the truck is hot and idling. At idle it will creep to about 210 and will drop all the way to cold as soon as you step on the gas. I’m stumped Link to comment Share on other sites More sharing options...
Eagle Posted December 13, 2007 Share Posted December 13, 2007 Not to hijack your thread but I’m having a very strange coolant temp gauge issue at the moment too. The gauge originally worked ok but was very active, it would bounce between ¼ and ½ and twitch around all the time. In July the gauge finally gave out and would spin wildly about, to the point where it would go 360 around and look like a propeller. I figured the gauge was shot. This is in an 87? How can the gauge have spun like a propeller -- it isn't a center pivot gauge, the 87 should be a bottom pivot gauge and it only swings through about a 90 degree arc. I had an 84 XJ 4-cyl that DID have a center pivot gauge, and that one gyrated wildly. Turned out the connector that pushes onto the top of the sender was fubar. I cut it off, soldered on a ring connector, and used a nut and lock washer to make the connection (the post on the sender is threaded, thankfully). End of problem. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted December 14, 2007 Share Posted December 14, 2007 nope, 87 is center pivot just like 88 on up Link to comment Share on other sites More sharing options...
Eagle Posted December 14, 2007 Share Posted December 14, 2007 ^^^ Check. Center pivot, but only a 90-degree swing (actually, even less than 90-degree). No way it can spin like an airplane propeller. There are pins at both limits Link to comment Share on other sites More sharing options...
Car RamRod Posted December 14, 2007 Author Share Posted December 14, 2007 eagle; funny that you picked that picture....I bought that cluster and it's in my mj now. Anywho, changed the sensor and its all good. It reads about 10* hot, but as long as it's consistent I'm happy. Cooling system is under control as well. I seem to have it all buttoned up correctly. Link to comment Share on other sites More sharing options...
1987Comanche Posted December 14, 2007 Share Posted December 14, 2007 Yes, it's a center pivot gauge. Actually I think all the peripheral gauges are (oil press, batt voltage, etc). I changed the CTS but I haven't taken a close look at the connector in the wiring harness. What should I be looking for Eagle? Was yours just trashed or was it more subtle than that? Link to comment Share on other sites More sharing options...
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