UNL1MTD Posted November 27, 2008 Share Posted November 27, 2008 I recently swapped in a full gauge cluster. Ever since, after the MJ gets hot and has been running the temp gauge starts to do this pattern where it starts at 210 then goes up very very slowly to 230 ish (the next white line). It nevers hits the red or goes past the 230 line. Then it falls very fast back to 210 and stays there for a minute or two, then repeats. The coolant level is good. Thats about all I know at this point. '87 Mj 4.0L 2wd, Stock cooling system. This can't be normal. Any ideas? Link to comment Share on other sites More sharing options...
Eagle Posted November 27, 2008 Share Posted November 27, 2008 I recently swapped in a full gauge cluster. Ever since, after the MJ gets hot and has been running the temp gauge starts to do this pattern where it starts at 210 then goes up very very slowly to 230 ish (the next white line). It nevers hits the red or goes past the 230 line. Then it falls very fast back to 210 and stays there for a minute or two, then repeats. The coolant level is good. Thats about all I know at this point. '87 Mj 4.0L 2wd, Stock cooling system. This can't be normal. Any ideas? You may need a viscous fan clutch, or you may need a radiator. What's happening is the primary fan can't pull enough air through the radiator to cool the engine. It gets to 230 and the auxiliary fan kicks in. That pulls more air, the temperature drops to where it should be ... and the cycle repeats. Link to comment Share on other sites More sharing options...
HOrnbrod Posted November 27, 2008 Share Posted November 27, 2008 First question is what were the temp characteristics before the gauge swap? Did the idiot light ever come on? If not, maybe you are seeing what was happening before with the fan clutch that the idiot light could not pick up, as Eagle says, maybe not. You might have a bad temp gauge, sensor, or wiring from the sensor to the gauge. But first grab an external laser thermometer and verify what is happening with the temp at the sensor hole w. the laser (or infrared). Link to comment Share on other sites More sharing options...
UNL1MTD Posted November 27, 2008 Author Share Posted November 27, 2008 I recently swapped in a full gauge cluster. Ever since, after the MJ gets hot and has been running the temp gauge starts to do this pattern where it starts at 210 then goes up very very slowly to 230 ish (the next white line). It nevers hits the red or goes past the 230 line. Then it falls very fast back to 210 and stays there for a minute or two, then repeats. The coolant level is good. Thats about all I know at this point. '87 Mj 4.0L 2wd, Stock cooling system. This can't be normal. Any ideas? You may need a viscous fan clutch, or you may need a radiator. What's happening is the primary fan can't pull enough air through the radiator to cool the engine. It gets to 230 and the auxiliary fan kicks in. That pulls more air, the temperature drops to where it should be ... and the cycle repeats. Although I have an aux fan its not wired in yet. My truck is a super base model. Manual, no ac, hence no aux fan. Link to comment Share on other sites More sharing options...
UNL1MTD Posted November 27, 2008 Author Share Posted November 27, 2008 First question is what were the temp characteristics before the gauge swap? Did the idiot light ever come on? If not, maybe you are seeing what was happening before with the fan clutch that the idiot light could not pick up, as Eagle says, maybe not. You might have a bad temp gauge, sensor, or wiring from the sensor to the gauge. But first grab an external laser thermometer and verify what is happening with the temp at the sensor hole w. the laser (or infrared). Good idea on the laser thermometer, I can borrow one from work. Before hand with idiot lights, I had no signs of anything going on. Never once did they come on. Last novemember I replaced the pressure bottle and cap, then flushed the coolant. Any chance there is an air pocket lingering around? Link to comment Share on other sites More sharing options...
Eagle Posted November 27, 2008 Share Posted November 27, 2008 No aux fan? Try changing your thermostat. Does it tend to get hotter when you're stopped, and drop back to 210 when you start rolling? Or does it do this little needle dance while you're rolling down the highway at 65 MPH? Link to comment Share on other sites More sharing options...
UNL1MTD Posted November 28, 2008 Author Share Posted November 28, 2008 No aux fan? Try changing your thermostat. Does it tend to get hotter when you're stopped, and drop back to 210 when you start rolling? Or does it do this little needle dance while you're rolling down the highway at 65 MPH? Yea I did buy an aux fan last summer, but never got around to wiring it to an aux switch. It does it while sitting at idle or rolling down the highway at 65 mph. Link to comment Share on other sites More sharing options...
BLHTAZ Posted November 28, 2008 Share Posted November 28, 2008 This may sound like a dumb question, but...did you remember to change the temp switch (for a light) to the sender for the guage? They look pretty much the same, but operate completely different. I ASSume that you did change it, but had to ask...so check the temp as suggested and if that's good, then you likely have a bad guage. It happened to me with my oil pressure guage when I did the swap and I had to replace the guage. :cheers: Link to comment Share on other sites More sharing options...
UNL1MTD Posted November 28, 2008 Author Share Posted November 28, 2008 This may sound like a dumb question, but...did you remember to change the temp switch (for a light) to the sender for the guage? They look pretty much the same, but operate completely different. I ASSume that you did change it, but had to ask...so check the temp as suggested and if that's good, then you likely have a bad guage. It happened to me with my oil pressure guage when I did the swap and I had to replace the guage. :cheers: Are you asking if I changed the Temp sender for the guage rather than leave the old idiot light sender in? I did change it out. But perhaps its bad. I'll get access to a laser thermometer on Monday, I'll check then. Link to comment Share on other sites More sharing options...
Eagle Posted November 28, 2008 Share Posted November 28, 2008 The periodic fluctuation is not indicative of either a bad sensor or a bad gauge. If it's not being caused by the aux fan cutting in, and it's not just at idle (indicating a bad fan clutch), it is most likely the gauge responding to opening and closing of the thermostat. Remember, a thermostat is intended to keep the temperature UP, not down. The thermostat stays closed until the coolant reaches the prescribed temperature, then it opens. There's a range of something like 15 degrees that the temperature then has to drop before the thermostat closes again. I think you are seeing the thermostat doing what it's supposed to be doing, except that it seems to be doing it a few degrees too hot. That's why I recommend replacing it. Get it from a Jeep dealer. It seems only the official Mopar thermostat has the air bleed vent in the top of the flange, and without that bleed hole you'll have a hard time purging air from the system. Link to comment Share on other sites More sharing options...
BLHTAZ Posted November 28, 2008 Share Posted November 28, 2008 OK...one other thing that I have seen cause problems is the use of a sealer or sealing tape on the threads of a sender. If you put any kind of sealer or tape on it, clean it off ;) . Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted November 28, 2008 Share Posted November 28, 2008 Or it could be the "Chico syndrome" where evrything is brand new and fine and it just does this normally. You've described my exact situation to a tee and everything related to the cooling system is brand new. I've kept the needle at around 210* by running the aux fan fulltime and keeping the HVAC system on full blast all the time. Good luck fixing it and let me know if you come up with anything new. Link to comment Share on other sites More sharing options...
UNL1MTD Posted December 2, 2008 Author Share Posted December 2, 2008 I got the laser thermometer out today and did my best to get some accurate readings. It seems the larger coolant hose coming from the thermostat housing is always 10 to 15 degrees colder than the smaller coolant hose coming from ther thermomstat. I seemed to get the most accurate temp readings from shooting the block directly next to the thermostat housing. The readings were near identical to the gauge, it would vary from 208 up to 225 degrees. The thermometer showed the same oscillation in temp that the gauge did. This gives me confidence that the gauge and sender are accurate and I truely have a problem. I'm going to change out the thermostat and hopefully that helps. I will likely use dealer parts as long as they are resonable. Does anyone have a part number by chance? Besides the thermostat, should I be changing out any hoses or do I just wait until I can get them off and give them an inspection? Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 3, 2008 Share Posted December 3, 2008 Does anyone have a part number by chance? Besides the thermostat, should I be changing out any hoses or do I just wait until I can get them off and give them an inspection? Dealer p/n is 83501426AC, comes with the gasket, about $12. I'd just replace it. Link to comment Share on other sites More sharing options...
UNL1MTD Posted December 3, 2008 Author Share Posted December 3, 2008 Thanks for the part number. I was looking at the Haynes Manual for replacing the thermostat and it had a test procedure. But the first disclaimer was to check serp belt for proper tension. I did just recently change out my serp belt. I'm assuming this has to be checked for proper tension because if it wasn't the fan would not spin at the correct RPM. I'm assuming that since mine can cool itself that this is working correctly. I know I checked the tension when the belt was installed, but I will have to double check. Or is there something else gong on with the serp belt that affects cooling? Link to comment Share on other sites More sharing options...
jaekl Posted December 3, 2008 Share Posted December 3, 2008 My 4 cylinder does the same thing but from indicated 160 to 210. 160 is probably what the normal temp should be. Seeing how rapidly is falls, I fairly sure it's thermostat and must be a bit sensitive. The dwell angle reduces with time and settles down. With my temps, I'm not concerned. My new issue is the voltmeter. The indicated value has dropped way below 14 volts but the measured voltage at the battery with and without the alternator is as it should be. Must have a voltage drop some where, but sometimes it will almost get up to 13 volts. Link to comment Share on other sites More sharing options...
UNL1MTD Posted December 14, 2008 Author Share Posted December 14, 2008 I'm chaning the Thermostat out today and I notice that the Mopar kit comes with 3 gaskets. Its obvious that one is for the housing mating to the block, but the other two are not obvious to me. One has 4 holes, its shaped sorta like the tstat housing, but not really. The other has one hole and is about the size of the thermostat. Haynes manual only mentions one gasket. I'm a bit perplexed. The MJ is apart right now, please chime in. Link to comment Share on other sites More sharing options...
UNL1MTD Posted December 14, 2008 Author Share Posted December 14, 2008 I'm chaning the Thermostat out today and I notice that the Mopar kit comes with 3 gaskets. Its obvious that one is for the housing mating to the block, but the other two are not obvious to me. One has 4 holes, its shaped sorta like the tstat housing, but not really. The other has one hole and is about the size of the thermostat. Haynes manual only mentions one gasket. I'm a bit perplexed. The MJ is apart right now, please chime in. Link to comment Share on other sites More sharing options...
BLHTAZ Posted December 14, 2008 Share Posted December 14, 2008 It's a universal kit...just use the one that matches and throw the other two away. ;) Link to comment Share on other sites More sharing options...
BLHTAZ Posted December 14, 2008 Share Posted December 14, 2008 It's a universal kit...just use the one that matches and throw the other two away. ;) Link to comment Share on other sites More sharing options...
UNL1MTD Posted December 14, 2008 Author Share Posted December 14, 2008 It's a universal kit...just use the one that matches and throw the other two away. ;) Thanks, I was trying to talk myself into using the smallest gasket aswell. I'm glad you posted. I wasnt able to start the truck due to not having enough coolant. I'll have to update you guys tomorrow. Does anyone know if the small upper radiator hose comes as a set with the heater control valve? I was thinking of replacing it but wasnt sure if I had to replace that whole assembly as well. Link to comment Share on other sites More sharing options...
UNL1MTD Posted December 14, 2008 Author Share Posted December 14, 2008 It's a universal kit...just use the one that matches and throw the other two away. ;) Thanks, I was trying to talk myself into using the smallest gasket aswell. I'm glad you posted. I wasnt able to start the truck due to not having enough coolant. I'll have to update you guys tomorrow. Does anyone know if the small upper radiator hose comes as a set with the heater control valve? I was thinking of replacing it but wasnt sure if I had to replace that whole assembly as well. Link to comment Share on other sites More sharing options...
Wildman Posted December 15, 2008 Share Posted December 15, 2008 You can buy any of the heater hoses each - Rockauto The factory crimp fitting, you can slice one side of them, and pry them off, and use hose clamps as a replacement :D Link to comment Share on other sites More sharing options...
Wildman Posted December 15, 2008 Share Posted December 15, 2008 You can buy any of the heater hoses each - Rockauto The factory crimp fitting, you can slice one side of them, and pry them off, and use hose clamps as a replacement :D Link to comment Share on other sites More sharing options...
UNL1MTD Posted December 15, 2008 Author Share Posted December 15, 2008 :fs1: started her up today and it took about 20 seconds before I had a steady stream of coolant pissing out from the Tstat housing. I don't suppose I can reuse that gasket, can I? Was it a mistake to put RTV on both sides of the gasket like it is recommended in the Haynes manual? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now